Re: [RFC PATCH v3 7/7] arm: dma-mapping: plumb our iommu mapping ops into arch_setup_dma_ops
On Fri, Oct 03, 2014 at 04:08:50PM +0100, Will Deacon wrote: Hi Thierry, On Wed, Oct 01, 2014 at 09:46:10AM +0100, Thierry Reding wrote: On Tue, Sep 30, 2014 at 05:00:35PM +0100, Will Deacon wrote: On Thu, Sep 25, 2014 at 07:40:23AM +0100, Thierry Reding wrote: [...] So I think what we're going to need is a way to prevent the default attachment to DMA/IOMMU. Or alternatively not associate devices with IOMMU domains by default but let drivers explicitly make the decision. Which drivers and how would they know what to do? I think you might be jumping the gun a bit here, given where mainline is with using the IOMMU for anything at all. I don't think I am. I've been working on patches to enable IOMMU on Tegra, with the specific use-case that we want to use it to allow physically non-contiguous framebuffers to be used for scan out. In order to do so the DRM driver allocates an IOMMU domain and adds both display controllers to it. When a framebuffer is created or imported from DMA-BUF, it gets mapped into this domain and both display controllers can use the IOVA address as the framebuffer base address. Does that mean you manually swizzle the dma_map_ops for the device in the DRM driver? No. It means we use the IOMMU API directly instead of the DMA mapping API. Given that a device can only be attached to a single domain at a time this will cause breakage when the ARM glue code starts automatically attaching the display controllers to a default domain. Why couldn't you just re-use the domain already allocated by the DMA mapping API? Because I don't see how you'd get access to it. And provided that we could do that it would also mean that there'd be at least two domains (one for each display controller) and we'd need to decide on using a single one of them. Which one do we choose? And what about the unused one? If there's no way to detach it we loose a precious resource. What I proposed a while back was to leave it up to the IOMMU driver to choose an allocator for the device. Or rather, choose whether to use a custom allocator or the DMA/IOMMU integration allocator. The way this worked was to keep a list of devices in the IOMMU driver. Devices in this list would be added to domain reserved for DMA/IOMMU integration. Those would typically be devices such as SD/MMC, audio, ... devices that are in-kernel and need no per-process separation. By default devices wouldn't be added to a domain, so devices forming a composite DRM device would be able to manage their own domain. I'd live to have as little of this as possible in the IOMMU drivers, as we should leave those to deal with the IOMMU hardware and not domain management. Having subsystems manage their own dma ops is an extension to the dma-mapping API. It's not an extension, really. It's more that both need to be able to coexist. For some devices you may want to create an IOMMU domain and hook it up with the DMA mapping functions, for others you don't and handle mapping to IOVA space explicitly. I think it's an extension in the sense that mainline doesn't currently do what you want, regardless of this patch series. It's interesting since you're now the second person to say this. Can you please elaborate why you think that's the case? Because the only way to set up DMA through an IOMMU on ARM is via the arm_iommu_* functions, No, you can use the IOMMU API directly just fine. which are currently called from a subset of the IOMMU drivers themselves: drivers/gpu/drm/exynos/exynos_drm_iommu.c drivers/iommu/ipmmu-vmsa.c drivers/iommu/shmobile-iommu.c drivers/media/platform/omap3isp/isp.c Of these, ipmmu-vmsa.c and shmobile.c both allocate a domain per device. The omap3 code seems to do something similar. That just leaves the exynos driver, which Marek has been reworking anyway. Right, and as I remember one of the things that Marek did was introduce a flag to mark drivers as doing their own IOMMU domain management so that they wouldn't be automatically associated with a mapping. I do have local patches that allow precisely this use-case to work without changes to the IOMMU core or requiring any extra ARM-specific glue. There's a fair bit of jumping through hoops, because for example you don't know what IOMMU instance a domain belongs to at .domain_init() time, so I have to defer most of the actual domain initalization until a device is actually attached to it, but I digress. Doing so would leave a large number of address spaces available for things like a GPU driver to keep per-process address spaces for isolation. I don't see how we'd be able to do that with the approach that you propose in this series since it assumes that each device will be associated
Re: [RFC PATCH v3 7/7] arm: dma-mapping: plumb our iommu mapping ops into arch_setup_dma_ops
Hi Thierry and Will, On Monday 06 October 2014 11:52:50 Thierry Reding wrote: On Fri, Oct 03, 2014 at 04:08:50PM +0100, Will Deacon wrote: On Wed, Oct 01, 2014 at 09:46:10AM +0100, Thierry Reding wrote: On Tue, Sep 30, 2014 at 05:00:35PM +0100, Will Deacon wrote: On Thu, Sep 25, 2014 at 07:40:23AM +0100, Thierry Reding wrote: [...] So I think what we're going to need is a way to prevent the default attachment to DMA/IOMMU. Or alternatively not associate devices with IOMMU domains by default but let drivers explicitly make the decision. Which drivers and how would they know what to do? I think you might be jumping the gun a bit here, given where mainline is with using the IOMMU for anything at all. I don't think I am. I've been working on patches to enable IOMMU on Tegra, with the specific use-case that we want to use it to allow physically non-contiguous framebuffers to be used for scan out. In order to do so the DRM driver allocates an IOMMU domain and adds both display controllers to it. When a framebuffer is created or imported from DMA-BUF, it gets mapped into this domain and both display controllers can use the IOVA address as the framebuffer base address. Does that mean you manually swizzle the dma_map_ops for the device in the DRM driver? No. It means we use the IOMMU API directly instead of the DMA mapping API. Is there a reason why you can't use the DMA mapping API for this, assuming of course that it would provide a way to attach both display controllers to the same domain ? Do you need to have explicit control over the VA at which the buffers are mapped ? Given that a device can only be attached to a single domain at a time this will cause breakage when the ARM glue code starts automatically attaching the display controllers to a default domain. Why couldn't you just re-use the domain already allocated by the DMA mapping API? Because I don't see how you'd get access to it. And provided that we could do that it would also mean that there'd be at least two domains (one for each display controller) and we'd need to decide on using a single one of them. Which one do we choose? And what about the unused one? If there's no way to detach it we loose a precious resource. This would also be an issue for my Renesas IOMMU (ipmmu-vmsa) use cases. The IOMMU supports up to four domains (each of them having its own hardware TLB) and shares them between all the bus masters connected to the IOMMU. The connections between bus master and TLBs are configurable. I thus can't live with one domain being created per device. What I proposed a while back was to leave it up to the IOMMU driver to choose an allocator for the device. Or rather, choose whether to use a custom allocator or the DMA/IOMMU integration allocator. The way this worked was to keep a list of devices in the IOMMU driver. Devices in this list would be added to domain reserved for DMA/IOMMU integration. Those would typically be devices such as SD/MMC, audio, ... devices that are in-kernel and need no per-process separation. By default devices wouldn't be added to a domain, so devices forming a composite DRM device would be able to manage their own domain. The problem with your solution is that it requires knowledge of all bus master devices in the IOMMU driver. That's not where that knowledge belongs, as it's a property of a particular SoC integration, not of the IOMMU itself. I'd live to have as little of this as possible in the IOMMU drivers, as we should leave those to deal with the IOMMU hardware and not domain management. Having subsystems manage their own dma ops is an extension to the dma-mapping API. It's not an extension, really. It's more that both need to be able to coexist. For some devices you may want to create an IOMMU domain and hook it up with the DMA mapping functions, for others you don't and handle mapping to IOVA space explicitly. I think it's an extension in the sense that mainline doesn't currently do what you want, regardless of this patch series. It's interesting since you're now the second person to say this. Can you please elaborate why you think that's the case? Because the only way to set up DMA through an IOMMU on ARM is via the arm_iommu_* functions, No, you can use the IOMMU API directly just fine. which are currently called from a subset of the IOMMU drivers themselves: drivers/gpu/drm/exynos/exynos_drm_iommu.c drivers/iommu/ipmmu-vmsa.c drivers/iommu/shmobile-iommu.c drivers/media/platform/omap3isp/isp.c Of these, ipmmu-vmsa.c and shmobile.c both allocate a domain per device. The omap3 code seems to do something similar. That just leaves the exynos driver, which Marek has been reworking anyway. Right, and as I remember one of the things that Marek did was introduce a flag to mark drivers as doing their own IOMMU domain management
Re: [RFC PATCH v3 7/7] arm: dma-mapping: plumb our iommu mapping ops into arch_setup_dma_ops
On Mon, Oct 06, 2014 at 01:50:40PM +0300, Laurent Pinchart wrote: Hi Thierry and Will, On Monday 06 October 2014 11:52:50 Thierry Reding wrote: On Fri, Oct 03, 2014 at 04:08:50PM +0100, Will Deacon wrote: On Wed, Oct 01, 2014 at 09:46:10AM +0100, Thierry Reding wrote: On Tue, Sep 30, 2014 at 05:00:35PM +0100, Will Deacon wrote: On Thu, Sep 25, 2014 at 07:40:23AM +0100, Thierry Reding wrote: [...] So I think what we're going to need is a way to prevent the default attachment to DMA/IOMMU. Or alternatively not associate devices with IOMMU domains by default but let drivers explicitly make the decision. Which drivers and how would they know what to do? I think you might be jumping the gun a bit here, given where mainline is with using the IOMMU for anything at all. I don't think I am. I've been working on patches to enable IOMMU on Tegra, with the specific use-case that we want to use it to allow physically non-contiguous framebuffers to be used for scan out. In order to do so the DRM driver allocates an IOMMU domain and adds both display controllers to it. When a framebuffer is created or imported from DMA-BUF, it gets mapped into this domain and both display controllers can use the IOVA address as the framebuffer base address. Does that mean you manually swizzle the dma_map_ops for the device in the DRM driver? No. It means we use the IOMMU API directly instead of the DMA mapping API. Is there a reason why you can't use the DMA mapping API for this, assuming of course that it would provide a way to attach both display controllers to the same domain ? Do you need to have explicit control over the VA at which the buffers are mapped ? I suppose I could use the DMA mapping API at least for the display parts if both controllers could be attached to the same domain. However when we get to the 2D and 3D parts we will probably want to switch the IOMMU domain depending on the userspace context to prevent applications from stepping on each other's toes. And no, I don't need to have explicit control over which VA the buffers get mapped to. Given that a device can only be attached to a single domain at a time this will cause breakage when the ARM glue code starts automatically attaching the display controllers to a default domain. Why couldn't you just re-use the domain already allocated by the DMA mapping API? Because I don't see how you'd get access to it. And provided that we could do that it would also mean that there'd be at least two domains (one for each display controller) and we'd need to decide on using a single one of them. Which one do we choose? And what about the unused one? If there's no way to detach it we loose a precious resource. This would also be an issue for my Renesas IOMMU (ipmmu-vmsa) use cases. The IOMMU supports up to four domains (each of them having its own hardware TLB) and shares them between all the bus masters connected to the IOMMU. The connections between bus master and TLBs are configurable. I thus can't live with one domain being created per device. I suppose one could fake this behind the curtains by making several domains correspond to the same TLB (it sounds like pretty much the same concept as an address space on Tegra). But that's just really nasty in my opinion. What I proposed a while back was to leave it up to the IOMMU driver to choose an allocator for the device. Or rather, choose whether to use a custom allocator or the DMA/IOMMU integration allocator. The way this worked was to keep a list of devices in the IOMMU driver. Devices in this list would be added to domain reserved for DMA/IOMMU integration. Those would typically be devices such as SD/MMC, audio, ... devices that are in-kernel and need no per-process separation. By default devices wouldn't be added to a domain, so devices forming a composite DRM device would be able to manage their own domain. The problem with your solution is that it requires knowledge of all bus master devices in the IOMMU driver. That's not where that knowledge belongs, as it's a property of a particular SoC integration, not of the IOMMU itself. Right. It will work nicely on Tegra where the IOMMU is closely tied to the memory controller and therefore does in fact know about all of the masters. It won't work for something more generic like the ARM SMMU where the SoC integration really isn't a property of the IOMMU itself. So Marek's proposal to mark drivers that don't need or want the DMA API integration sounds like a pretty good alternative to me. Yes, that's the plan. Having thought about it some more (after your comments), subsystems can still call of_dma_deconfigure if they want to do their own IOMMU domain management. That may well be useful for things like VFIO, for example. I think it's really weird to set up some complicated
Re: [RFC PATCH v3 7/7] arm: dma-mapping: plumb our iommu mapping ops into arch_setup_dma_ops
Hi Thierry, On Wed, Oct 01, 2014 at 09:46:10AM +0100, Thierry Reding wrote: On Tue, Sep 30, 2014 at 05:00:35PM +0100, Will Deacon wrote: On Thu, Sep 25, 2014 at 07:40:23AM +0100, Thierry Reding wrote: [...] So I think what we're going to need is a way to prevent the default attachment to DMA/IOMMU. Or alternatively not associate devices with IOMMU domains by default but let drivers explicitly make the decision. Which drivers and how would they know what to do? I think you might be jumping the gun a bit here, given where mainline is with using the IOMMU for anything at all. I don't think I am. I've been working on patches to enable IOMMU on Tegra, with the specific use-case that we want to use it to allow physically non-contiguous framebuffers to be used for scan out. In order to do so the DRM driver allocates an IOMMU domain and adds both display controllers to it. When a framebuffer is created or imported from DMA-BUF, it gets mapped into this domain and both display controllers can use the IOVA address as the framebuffer base address. Does that mean you manually swizzle the dma_map_ops for the device in the DRM driver? Given that a device can only be attached to a single domain at a time this will cause breakage when the ARM glue code starts automatically attaching the display controllers to a default domain. Why couldn't you just re-use the domain already allocated by the DMA mapping API? What I proposed a while back was to leave it up to the IOMMU driver to choose an allocator for the device. Or rather, choose whether to use a custom allocator or the DMA/IOMMU integration allocator. The way this worked was to keep a list of devices in the IOMMU driver. Devices in this list would be added to domain reserved for DMA/IOMMU integration. Those would typically be devices such as SD/MMC, audio, ... devices that are in-kernel and need no per-process separation. By default devices wouldn't be added to a domain, so devices forming a composite DRM device would be able to manage their own domain. I'd live to have as little of this as possible in the IOMMU drivers, as we should leave those to deal with the IOMMU hardware and not domain management. Having subsystems manage their own dma ops is an extension to the dma-mapping API. It's not an extension, really. It's more that both need to be able to coexist. For some devices you may want to create an IOMMU domain and hook it up with the DMA mapping functions, for others you don't and handle mapping to IOVA space explicitly. I think it's an extension in the sense that mainline doesn't currently do what you want, regardless of this patch series. It's interesting since you're now the second person to say this. Can you please elaborate why you think that's the case? Because the only way to set up DMA through an IOMMU on ARM is via the arm_iommu_* functions, which are currently called from a subset of the IOMMU drivers themselves: drivers/gpu/drm/exynos/exynos_drm_iommu.c drivers/iommu/ipmmu-vmsa.c drivers/iommu/shmobile-iommu.c drivers/media/platform/omap3isp/isp.c Of these, ipmmu-vmsa.c and shmobile.c both allocate a domain per device. The omap3 code seems to do something similar. That just leaves the exynos driver, which Marek has been reworking anyway. I do have local patches that allow precisely this use-case to work without changes to the IOMMU core or requiring any extra ARM-specific glue. There's a fair bit of jumping through hoops, because for example you don't know what IOMMU instance a domain belongs to at .domain_init() time, so I have to defer most of the actual domain initalization until a device is actually attached to it, but I digress. Doing so would leave a large number of address spaces available for things like a GPU driver to keep per-process address spaces for isolation. I don't see how we'd be able to do that with the approach that you propose in this series since it assumes that each device will be associated with a separate domain. No, that's an artifact of the existing code on ARM. My series adds a list of domains to each device, but those domains are per-IOMMU instance and can appear in multiple lists. So you're saying the end result will be that there's a single domain per IOMMU device that will be associated with all devices that have a master interface to it? Yes, that's the plan. Having thought about it some more (after your comments), subsystems can still call of_dma_deconfigure if they want to do their own IOMMU domain management. That may well be useful for things like VFIO, for example. Will ___ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
Re: [RFC PATCH v3 7/7] arm: dma-mapping: plumb our iommu mapping ops into arch_setup_dma_ops
Hi Thierry, On Thu, Sep 25, 2014 at 07:40:23AM +0100, Thierry Reding wrote: On Wed, Sep 24, 2014 at 05:33:38PM +0100, Will Deacon wrote: On Tue, Sep 23, 2014 at 08:14:01AM +0100, Thierry Reding wrote: On Mon, Sep 22, 2014 at 06:43:37PM +0100, Will Deacon wrote: Yup. In this case, the iommu_dma_mapping passed to arch_setup_dma_ops contains a domain and an allocator for each IOMMU instance in the system. It would then be up to the architecture how it makes use of those, but the most obvious thing to do would be to attach devices mastering through an IOMMU instance to that per-instance domain. The other use-case is isolation (one domain per device), which I guess matches what the ARM code is doing at the moment. I think there are two cases here. You can have a composite device that wants to manage a single domain (using its own allocator) for a set of hardware devices. At the same time a set of devices (think 2D and 3D engines) could want to use a multiple domains for process separation. In that case I'd expect a logical DRM device to allocate one domain per process and then associate the 2D and 3D engines with that same domain on process switch. Sure, but that's well outside of what the dma-mapping API is going to setup as a default domain. These specialist setups are certainly possible, but I think they should be driven by, for example, the DRM code as opposed to being in the core dma-mapping code. I completely agree that these special cases should be driven by the drivers that need them. However the problem here is that the current patch will already attach the device to an IOMMU domain by default. Sure, but that's not an unfixable problem if somebody cares enough to do it. Right now, I see a small handful of callers for the IOMMU API and nearly all of them would work perfectly well with a default domain. The big exception to that is VFIO, but that requires the device to be unbound from the host driver, so we could detach the mapping at that point. So I think what we're going to need is a way to prevent the default attachment to DMA/IOMMU. Or alternatively not associate devices with IOMMU domains by default but let drivers explicitly make the decision. Which drivers and how would they know what to do? I think you might be jumping the gun a bit here, given where mainline is with using the IOMMU for anything at all. What I proposed a while back was to leave it up to the IOMMU driver to choose an allocator for the device. Or rather, choose whether to use a custom allocator or the DMA/IOMMU integration allocator. The way this worked was to keep a list of devices in the IOMMU driver. Devices in this list would be added to domain reserved for DMA/IOMMU integration. Those would typically be devices such as SD/MMC, audio, ... devices that are in-kernel and need no per-process separation. By default devices wouldn't be added to a domain, so devices forming a composite DRM device would be able to manage their own domain. I'd live to have as little of this as possible in the IOMMU drivers, as we should leave those to deal with the IOMMU hardware and not domain management. Having subsystems manage their own dma ops is an extension to the dma-mapping API. It's not an extension, really. It's more that both need to be able to coexist. For some devices you may want to create an IOMMU domain and hook it up with the DMA mapping functions, for others you don't and handle mapping to IOVA space explicitly. I think it's an extension in the sense that mainline doesn't currently do what you want, regardless of this patch series. My motivation is to enable IOMMU-backed DMA-mapping so that I can continue implementing the virtual SMMU work I started a while back. Patches welcome to enable any other use-cases -- I don't think they're mutually exclusive. There is another issue with the approach you propose. I'm not sure if Tegra is special in this case (I'd expect not), but what we do is make an IOMMU domain correspond to an address space. Address spaces are a pretty limited resource (earlier generations have 4, newer have 128) and each address space can be up to 4 GiB. So I've always envisioned that we should be using a single IOMMU domain for devices that don't expose direct buffer access to userspace (SATA, PCIe, audio, SD/MMC, USB, ...). All of those would typically need only a small number of small buffers, so using a separate address space for each seems like a big waste. I agree here, the ARM DMA-mapping code should really be doing one domain per SMMU instance; all I've done is hook up the existing code which wasn't previously being called. Doing so would leave a large number of address spaces available for things like a GPU driver to keep per-process address spaces for isolation. I don't see how we'd be able to do that with the approach that you propose in this
Re: [RFC PATCH v3 7/7] arm: dma-mapping: plumb our iommu mapping ops into arch_setup_dma_ops
On Wed, Sep 24, 2014 at 05:33:38PM +0100, Will Deacon wrote: On Tue, Sep 23, 2014 at 08:14:01AM +0100, Thierry Reding wrote: On Mon, Sep 22, 2014 at 06:43:37PM +0100, Will Deacon wrote: Yup. In this case, the iommu_dma_mapping passed to arch_setup_dma_ops contains a domain and an allocator for each IOMMU instance in the system. It would then be up to the architecture how it makes use of those, but the most obvious thing to do would be to attach devices mastering through an IOMMU instance to that per-instance domain. The other use-case is isolation (one domain per device), which I guess matches what the ARM code is doing at the moment. I think there are two cases here. You can have a composite device that wants to manage a single domain (using its own allocator) for a set of hardware devices. At the same time a set of devices (think 2D and 3D engines) could want to use a multiple domains for process separation. In that case I'd expect a logical DRM device to allocate one domain per process and then associate the 2D and 3D engines with that same domain on process switch. Sure, but that's well outside of what the dma-mapping API is going to setup as a default domain. These specialist setups are certainly possible, but I think they should be driven by, for example, the DRM code as opposed to being in the core dma-mapping code. I completely agree that these special cases should be driven by the drivers that need them. However the problem here is that the current patch will already attach the device to an IOMMU domain by default. So I think what we're going to need is a way to prevent the default attachment to DMA/IOMMU. Or alternatively not associate devices with IOMMU domains by default but let drivers explicitly make the decision. Either of those two alternatives would require driver-specific knowledge, which would be another strong argument against doing the whole IOMMU initialization at device creation time. What I proposed a while back was to leave it up to the IOMMU driver to choose an allocator for the device. Or rather, choose whether to use a custom allocator or the DMA/IOMMU integration allocator. The way this worked was to keep a list of devices in the IOMMU driver. Devices in this list would be added to domain reserved for DMA/IOMMU integration. Those would typically be devices such as SD/MMC, audio, ... devices that are in-kernel and need no per-process separation. By default devices wouldn't be added to a domain, so devices forming a composite DRM device would be able to manage their own domain. I'd live to have as little of this as possible in the IOMMU drivers, as we should leave those to deal with the IOMMU hardware and not domain management. Having subsystems manage their own dma ops is an extension to the dma-mapping API. It's not an extension, really. It's more that both need to be able to coexist. For some devices you may want to create an IOMMU domain and hook it up with the DMA mapping functions, for others you don't and handle mapping to IOVA space explicitly. There is another issue with the approach you propose. I'm not sure if Tegra is special in this case (I'd expect not), but what we do is make an IOMMU domain correspond to an address space. Address spaces are a pretty limited resource (earlier generations have 4, newer have 128) and each address space can be up to 4 GiB. So I've always envisioned that we should be using a single IOMMU domain for devices that don't expose direct buffer access to userspace (SATA, PCIe, audio, SD/MMC, USB, ...). All of those would typically need only a small number of small buffers, so using a separate address space for each seems like a big waste. Doing so would leave a large number of address spaces available for things like a GPU driver to keep per-process address spaces for isolation. I don't see how we'd be able to do that with the approach that you propose in this series since it assumes that each device will be associated with a separate domain. Thierry pgpl3vcqlop89.pgp Description: PGP signature ___ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
Re: [RFC PATCH v3 7/7] arm: dma-mapping: plumb our iommu mapping ops into arch_setup_dma_ops
On Tue, Sep 23, 2014 at 08:14:01AM +0100, Thierry Reding wrote: On Mon, Sep 22, 2014 at 06:43:37PM +0100, Will Deacon wrote: Yup. In this case, the iommu_dma_mapping passed to arch_setup_dma_ops contains a domain and an allocator for each IOMMU instance in the system. It would then be up to the architecture how it makes use of those, but the most obvious thing to do would be to attach devices mastering through an IOMMU instance to that per-instance domain. The other use-case is isolation (one domain per device), which I guess matches what the ARM code is doing at the moment. I think there are two cases here. You can have a composite device that wants to manage a single domain (using its own allocator) for a set of hardware devices. At the same time a set of devices (think 2D and 3D engines) could want to use a multiple domains for process separation. In that case I'd expect a logical DRM device to allocate one domain per process and then associate the 2D and 3D engines with that same domain on process switch. Sure, but that's well outside of what the dma-mapping API is going to setup as a default domain. These specialist setups are certainly possible, but I think they should be driven by, for example, the DRM code as opposed to being in the core dma-mapping code. What I proposed a while back was to leave it up to the IOMMU driver to choose an allocator for the device. Or rather, choose whether to use a custom allocator or the DMA/IOMMU integration allocator. The way this worked was to keep a list of devices in the IOMMU driver. Devices in this list would be added to domain reserved for DMA/IOMMU integration. Those would typically be devices such as SD/MMC, audio, ... devices that are in-kernel and need no per-process separation. By default devices wouldn't be added to a domain, so devices forming a composite DRM device would be able to manage their own domain. I'd live to have as little of this as possible in the IOMMU drivers, as we should leave those to deal with the IOMMU hardware and not domain management. Having subsystems manage their own dma ops is an extension to the dma-mapping API. Will ___ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
Re: [RFC PATCH v3 7/7] arm: dma-mapping: plumb our iommu mapping ops into arch_setup_dma_ops
On Fri, Sep 12, 2014 at 05:34:55PM +0100, Will Deacon wrote:
[...]
+static bool arm_setup_iommu_dma_ops(struct device *dev, u64 dma_base, u64
size)
+{
+ struct dma_iommu_mapping *mapping;
+
+ mapping = arm_iommu_create_mapping(dev-bus, dma_base, size);
If I understand correctly this will be called for each device that has
an IOMMU master interface and will end up creating a new mapping for
each of the devices. Each of these mappings will translate to a domain
in the IOMMU API, which in turn is a separate address space.
How do you envision to support use-cases where a set of devices need to
share a single domain? This is needed for example in DRM where SoCs
often have a set of hardware blocks (each with its own master interface)
that compose the display device. On Tegra for example there are two
display controllers that need access to the same IOVA domain so that
they can scan out framebuffers.
Thierry
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Re: [RFC PATCH v3 7/7] arm: dma-mapping: plumb our iommu mapping ops into arch_setup_dma_ops
On Monday 22 September 2014 11:19:35 Thierry Reding wrote:
On Fri, Sep 12, 2014 at 05:34:55PM +0100, Will Deacon wrote:
[...]
+static bool arm_setup_iommu_dma_ops(struct device *dev, u64 dma_base, u64
size) +{
+ struct dma_iommu_mapping *mapping;
+
+ mapping = arm_iommu_create_mapping(dev-bus, dma_base, size);
If I understand correctly this will be called for each device that has
an IOMMU master interface and will end up creating a new mapping for
each of the devices. Each of these mappings will translate to a domain
in the IOMMU API, which in turn is a separate address space.
How do you envision to support use-cases where a set of devices need to
share a single domain? This is needed for example in DRM where SoCs
often have a set of hardware blocks (each with its own master interface)
that compose the display device. On Tegra for example there are two
display controllers that need access to the same IOVA domain so that
they can scan out framebuffers.
Or simply for IOMMUs that serve multiple masters and support a single domain
only.
--
Regards,
Laurent Pinchart
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Re: [RFC PATCH v3 7/7] arm: dma-mapping: plumb our iommu mapping ops into arch_setup_dma_ops
Hi Thierry,
On Mon, Sep 22, 2014 at 10:19:35AM +0100, Thierry Reding wrote:
On Fri, Sep 12, 2014 at 05:34:55PM +0100, Will Deacon wrote:
[...]
+static bool arm_setup_iommu_dma_ops(struct device *dev, u64 dma_base, u64
size)
+{
+ struct dma_iommu_mapping *mapping;
+
+ mapping = arm_iommu_create_mapping(dev-bus, dma_base, size);
If I understand correctly this will be called for each device that has
an IOMMU master interface and will end up creating a new mapping for
each of the devices. Each of these mappings will translate to a domain
in the IOMMU API, which in turn is a separate address space.
Correct, although that's largely because I've bolted on the existing ARM
IOMMU code.
How do you envision to support use-cases where a set of devices need to
share a single domain? This is needed for example in DRM where SoCs
often have a set of hardware blocks (each with its own master interface)
that compose the display device. On Tegra for example there are two
display controllers that need access to the same IOVA domain so that
they can scan out framebuffers.
Yup. In this case, the iommu_dma_mapping passed to arch_setup_dma_ops
contains a domain and an allocator for each IOMMU instance in the system.
It would then be up to the architecture how it makes use of those, but
the most obvious thing to do would be to attach devices mastering through
an IOMMU instance to that per-instance domain.
The other use-case is isolation (one domain per device), which I guess
matches what the ARM code is doing at the moment.
Will
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