On Tue, Nov 11, 2003 at 10:50:01AM -0800, Ian Romanick wrote:
I must say that I am very impressed with how far the MGA driver has come since you started working on it. Now the only thing that's missing is support for PCI cards. ;)
A quick fix would be simply enabling PCI cards but keep the agpgart restriction. The only change required would be changing the access type to PCI in the DMA registers. I think it should work but I don't have a PCI card to test with so I can't be 100% sure.
So, I've now been tasked to actually do this. I get to enable support for a G450 PCI card that IBM ships in some of its POWER based systems. So, not only is it PCI & PPC64, but there is *no* AGP available at all. I haven't started actually changing any code as I don't have the hardware yet, but it's on the way.
I want to initially support this by just "disabling" AGP texturing. I looked in the DRI driver, and it looks like this can be done with some trivial changes in mga_xmesa.c. Basically, the code just needs to handle the case where serverInfo->agpTextureSize is 0. The DDX driver needs to be modified to detect PCI cards and do something smart there. I haven't looked in that code yet, but I'm guess it should be pretty trivial.
Then comes the kernel. :( I started looking that the ILOAD code in mga_state.c. Basically, it looks like everything assume the source buffers are in AGP space. I'm guessing that I could just look at the flags field in the drm_device_dma structure and only set the MGA_SRCACC_AGP bit if _DRM_DMA_USE_AGP bit is set. Is _DRM_DMA_USE_SG *always* set for PCI DMA transfers? I don't want to exclude the possability of sourcing vertex data from on-card memory in the future.
In the DRM, if there's no AGP available, then PCI memory has to be used for DMA. It looks like the setup for that happens in the DDX driver in MGADRIAgpInit (in mga_dri.c). In looking at that routine, it's not immediatly clear what to do. Obviously, DRM_AGP wouldn't be passed to any of the drmAddMap calls. Looking at radeon_dri.c, it looks like RADEONPciInit is the same as RADEONDRIAgpInit except it uses DRM_SCATTER_GATHER instead of DRM_AGP and drmScatterGatherAlloc instead of drmAgpAcquire / drmAgpAlloc / drmAgpBind. Is that right?
MGADRIPciInit wouldn't be a complete duplication of MGADRIAgpInit because I don't intend to (initially) support PCIGART. Even when PCIGART is supported, not all chips in the MGA family support it. Is the PCI G450 the only one?
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