On 2020-01-17 3:17 a.m., Christian König wrote:
Am 17.01.20 um 03:01 schrieb Felix Kuehling:
On 2020-01-16 8:09, Christian König wrote:
Coreboot seems to have a problem correctly setting up access to the
stolen VRAM
on KV/KB. Use the direct access only when necessary.
I'm not sure what you mean by "necessary".
Necessary for better performance.
Right. So your patch description says that sometimes better performance
is not necessary. The criteria is based on the size of the BAR, which
doesn't really have anything to do with performance.
Signed-off-by: Christian König <christian.koenig@xxxxxxx>
---
drivers/gpu/drm/amd/amdgpu/gmc_v7_0.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/amd/amdgpu/gmc_v7_0.c
b/drivers/gpu/drm/amd/amdgpu/gmc_v7_0.c
index 19d5b133e1d7..9da9596a3638 100644
--- a/drivers/gpu/drm/amd/amdgpu/gmc_v7_0.c
+++ b/drivers/gpu/drm/amd/amdgpu/gmc_v7_0.c
@@ -381,7 +381,8 @@ static int gmc_v7_0_mc_init(struct amdgpu_device
*adev)
adev->gmc.aper_size = pci_resource_len(adev->pdev, 0);
#ifdef CONFIG_X86_64
- if (adev->flags & AMD_IS_APU) {
+ if (adev->flags & AMD_IS_APU &&
+ adev->gmc.real_vram_size > adev->gmc.aper_size) {
CPU access to the whole VRAM isn't really necessary. I thought the
main motivation for accessing FB directly on APUs was better
performance. You're disabling that optimization on all APUs where the
FB is smaller than the aperture size.
Correct, yes. For some reason coreboot seems to explicitly setup the
memory used for the FB as write-protected.
The GPU can still read/write it normally cause it ignores that
protection, but the CPU can't change the FB memory any more with that
setup.
Can we test whether writing to FB works and make the decision based on that?
Thanks,
Felix
No idea why they do this, most likely just an over conservative
protection of a reserved area of memory.
Regards,
Christian.
Regards,
Felix
adev->gmc.aper_base = ((u64)RREG32(mmMC_VM_FB_OFFSET)) << 22;
adev->gmc.aper_size = adev->gmc.real_vram_size;
}
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