[RFC 2/6] drm/etnaviv: allow building etnaviv on omap devices

On Sat, Nov 19, 2016 at 03:58:15AM -0800, Joshua Clayton wrote:

On Friday, November 18, 2016 10:33:42 AM Rob Herring wrote:

quoted

On Thu, Nov 17, 2016 at 08:44:32PM -0600, Robert Nelson wrote:

quoted

Signed-off-by: Robert Nelson <redacted>
CC: Christian Gmeiner <christian.gmeiner@gmail.com>
CC: Russell King <redacted>
CC: Lucas Stach <l.stach@pengutronix.de>
---
 drivers/gpu/drm/etnaviv/Kconfig | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/etnaviv/Kconfig b/drivers/gpu/drm/etnaviv/Kconfig
index 2cde7a5..b776f41 100644
--- a/drivers/gpu/drm/etnaviv/Kconfig
+++ b/drivers/gpu/drm/etnaviv/Kconfig

@@ -2,7 +2,7 @@
 config DRM_ETNAVIV
 	tristate "ETNAVIV (DRM support for Vivante GPU IP cores)"
 	depends on DRM
-	depends on ARCH_MXC || ARCH_DOVE
+	depends on ARCH_MXC || ARCH_DOVE || ARCH_OMAP2PLUS

Why not just drop this line. Then it will get better build testing, too.

quoted

 	select SHMEM
 	select TMPFS
 	select IOMMU_API

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...building with ARCH=x86_64
            ^
drivers/gpu/drm/etnaviv/etnaviv_gpu.c: In function ?etnaviv_gpu_init?:
drivers/gpu/drm/etnaviv/etnaviv_gpu.c:633:18: error: ?PHYS_OFFSET? undeclared (first use in this function)
   if (dma_mask < PHYS_OFFSET + SZ_2G)
                  ^
drivers/gpu/drm/etnaviv/etnaviv_gpu.c:633:18: note: each undeclared identifier is reported only once for each function it appears in

... and that's why we don't drop the dependency, although changing it
to "depends on ARM" will open it up to wider build testing on other
ARM platforms, I don't think that gains very much.

The issue is that the command buffers must be located within the first
2GB of GPU virtual address space, and that space can only be translated
(offset).  What the code here is trying to do is to locate the 2GB of
virtual address space such that it overlaps the CMA region if RAM is
bigger than 2GB, or covers all of the RAM if not.

For that, we need to know where physical RAM starts.

I guess we could replace PHYS_OFFSET with virt_to_phys(PAGE_OFFSET)
here instead, which would be more arch-portable - although that would
be assuming there's no (system?) IOMMU between memory and the GPU.

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