Re: Q: Does mass storage gadget use DMA ?
Am Montag, den 26.02.2018, 18:09 +0200 schrieb Ran Shalit: > On Mon, Feb 26, 2018 at 5:59 PM, Oliver Neukum wrote: > > > > Am Donnerstag, den 15.02.2018, 11:00 +0200 schrieb Ran Shalit: > > > > > > I actually asked about DMA, because I see that it is possible to send > > > urb using DMA allocated buffers or not (coherent and non-coherent) > > > usb_buffer_alloc(). > > > So, How can we actually know if I should use this API with a device or > > > not ? I mean, is it always possible to use the coherent buffer with > > > the device ? > > > > Hi, > > > > it is always possible to use usb_alloc_coherent() on a host. > > But it is generally not sensible. It is for buffers to be reused > > many times. In general use kmalloc() [once per buffer. That is a rule. > > You must not share them.] > > > > HTH > > Oliver > > > Hi Oliver, > > Is the dma engine which is responsible for the transaction is actually > in the usb device (It's not dma controller in host) ? OK, I think there is a fundamental misunderstanding here. There are two sides: host and gadget Either, both or no side may use DMA. The other side does not learn of that. In either case, however, you write a driver for a logical device or a protocol, if you will. What we call a device driver on the host (the gadget has its own equivalents) does not talk to hardware. Essentially you allocate and manipulate URBs. There is a driver for a host (respectively gadget) controller which talks to hardware. It does DMA, not your driver. > If I understand correctly in both ways (kmalloc or > usb_alloc_coherent), then we are allocating buffers might be used for > dma. Yes. We must. > Even if DMA is not used in the transaction, than is shall still be > functional with the same DMA-allocated buffers. Yes. It must. HTH Oliver -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Q: Does mass storage gadget use DMA ?
On Mon, Feb 26, 2018 at 5:59 PM, Oliver Neukum wrote: > Am Donnerstag, den 15.02.2018, 11:00 +0200 schrieb Ran Shalit: >> I actually asked about DMA, because I see that it is possible to send >> urb using DMA allocated buffers or not (coherent and non-coherent) >> usb_buffer_alloc(). >> So, How can we actually know if I should use this API with a device or >> not ? I mean, is it always possible to use the coherent buffer with >> the device ? > > Hi, > > it is always possible to use usb_alloc_coherent() on a host. > But it is generally not sensible. It is for buffers to be reused > many times. In general use kmalloc() [once per buffer. That is a rule. > You must not share them.] > > HTH > Oliver > Hi Oliver, Is the dma engine which is responsible for the transaction is actually in the usb device (It's not dma controller in host) ? If I understand correctly in both ways (kmalloc or usb_alloc_coherent), then we are allocating buffers might be used for dma. Even if DMA is not used in the transaction, than is shall still be functional with the same DMA-allocated buffers. Thanks, ranran -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Q: Does mass storage gadget use DMA ?
Am Donnerstag, den 15.02.2018, 11:00 +0200 schrieb Ran Shalit: > I actually asked about DMA, because I see that it is possible to send > urb using DMA allocated buffers or not (coherent and non-coherent) > usb_buffer_alloc(). > So, How can we actually know if I should use this API with a device or > not ? I mean, is it always possible to use the coherent buffer with > the device ? Hi, it is always possible to use usb_alloc_coherent() on a host. But it is generally not sensible. It is for buffers to be reused many times. In general use kmalloc() [once per buffer. That is a rule. You must not share them.] HTH Oliver -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Q: Does mass storage gadget use DMA ?
On Thu, Feb 15, 2018 at 10:56 AM, Ran Shalit wrote: > On Mon, Feb 12, 2018 at 2:39 PM, Oliver Neukum wrote: >> Am Sonntag, den 11.02.2018, 22:17 +0200 schrieb Ran Shalit: >>> On Tue, Feb 6, 2018 at 8:55 AM, Felipe Balbi >>> wrote: >>> > >>> > >>> > Hi, >>> > >>> > Ran Shalit writes: >>> > > >>> > > Hello, >>> > > >>> > > I check code in: >>> > > https://elixir.free-electrons.com/linux/v3.3/source/drivers/usb/gadget/f_mass_storage.c >>> > > but I see no API usage of DMA, yet it is being mentioned as if it is >>> > > used. >>> > >>> > but it is used. It's just managed by the UDC driver (dwc3, musb, >>> > chipidea, Renesas, etc) >>> > >>> Just to be sure, >>> can I assume that other usb gadget drivers are using DMA (including >>> gadgetfs for userspace driver) ? >>> And it is also correct for host drivers (such as camera device ) ? >> >> None of these drivers are for hardware. They implement a protocol. >> On the host as well as on the gadget side there are driver for the >> actual host controllers (EHCI, XHCI, ...) as well as their gadget >> equivalents. >> >> Any of these drivers may or may not use DMA. Neither the assumption >> that they use DMA or the assumption that they do not use DMA >> is valid. In fact they may mix it. > Hi, I actually asked about DMA, because I see that it is possible to send urb using DMA allocated buffers or not (coherent and non-coherent) usb_buffer_alloc(). So, How can we actually know if I should use this API with a device or not ? I mean, is it always possible to use the coherent buffer with the device ? Sorry for the previous disrupted email, it was sent by mistake. Thanks a lot, Ran that there is API for dma > >> Your code must be ready to cope with either usage. >> >> HTH >> Oliver >> -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Q: Does mass storage gadget use DMA ?
On Mon, Feb 12, 2018 at 2:39 PM, Oliver Neukum wrote: > Am Sonntag, den 11.02.2018, 22:17 +0200 schrieb Ran Shalit: >> On Tue, Feb 6, 2018 at 8:55 AM, Felipe Balbi >> wrote: >> > >> > >> > Hi, >> > >> > Ran Shalit writes: >> > > >> > > Hello, >> > > >> > > I check code in: >> > > https://elixir.free-electrons.com/linux/v3.3/source/drivers/usb/gadget/f_mass_storage.c >> > > but I see no API usage of DMA, yet it is being mentioned as if it is >> > > used. >> > >> > but it is used. It's just managed by the UDC driver (dwc3, musb, >> > chipidea, Renesas, etc) >> > >> Just to be sure, >> can I assume that other usb gadget drivers are using DMA (including >> gadgetfs for userspace driver) ? >> And it is also correct for host drivers (such as camera device ) ? > > None of these drivers are for hardware. They implement a protocol. > On the host as well as on the gadget side there are driver for the > actual host controllers (EHCI, XHCI, ...) as well as their gadget > equivalents. > > Any of these drivers may or may not use DMA. Neither the assumption > that they use DMA or the assumption that they do not use DMA > is valid. In fact they may mix it. I asked about DMA > Your code must be ready to cope with either usage. > > HTH > Oliver > -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Q: Does mass storage gadget use DMA ?
Am Sonntag, den 11.02.2018, 22:17 +0200 schrieb Ran Shalit: > On Tue, Feb 6, 2018 at 8:55 AM, Felipe Balbi > wrote: > > > > > > Hi, > > > > Ran Shalit writes: > > > > > > Hello, > > > > > > I check code in: > > > https://elixir.free-electrons.com/linux/v3.3/source/drivers/usb/gadget/f_mass_storage.c > > > but I see no API usage of DMA, yet it is being mentioned as if it is used. > > > > but it is used. It's just managed by the UDC driver (dwc3, musb, > > chipidea, Renesas, etc) > > > Just to be sure, > can I assume that other usb gadget drivers are using DMA (including > gadgetfs for userspace driver) ? > And it is also correct for host drivers (such as camera device ) ? None of these drivers are for hardware. They implement a protocol. On the host as well as on the gadget side there are driver for the actual host controllers (EHCI, XHCI, ...) as well as their gadget equivalents. Any of these drivers may or may not use DMA. Neither the assumption that they use DMA or the assumption that they do not use DMA is valid. In fact they may mix it. Your code must be ready to cope with either usage. HTH Oliver -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Q: Does mass storage gadget use DMA ?
On Tue, Feb 6, 2018 at 8:55 AM, Felipe Balbi wrote: > > Hi, > > Ran Shalit writes: >> Hello, >> >> I check code in: >> https://elixir.free-electrons.com/linux/v3.3/source/drivers/usb/gadget/f_mass_storage.c >> but I see no API usage of DMA, yet it is being mentioned as if it is used. > > but it is used. It's just managed by the UDC driver (dwc3, musb, > chipidea, Renesas, etc) > Just to be sure, can I assume that other usb gadget drivers are using DMA (including gadgetfs for userspace driver) ? And it is also correct for host drivers (such as camera device ) ? Thanks, Ran > -- > balbi -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Q: Does mass storage gadget use DMA ?
Hi, Ran Shalit writes: > Hello, > > I check code in: > https://elixir.free-electrons.com/linux/v3.3/source/drivers/usb/gadget/f_mass_storage.c > but I see no API usage of DMA, yet it is being mentioned as if it is used. but it is used. It's just managed by the UDC driver (dwc3, musb, chipidea, Renesas, etc) -- balbi -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Q: Does mass storage gadget use DMA ?
Hi, Felipe Balbi writes: >> I check code in: >> https://elixir.free-electrons.com/linux/v3.3/source/drivers/usb/gadget/f_mass_storage.c ps: v3.3 realy??? You really need to upgrade that :-) -- balbi -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
