[PATCH] drm/amdgpu: fixup bad vram size on gmc v8

[Alex Deucher]

On Wed, Dec 15, 2021 at 10:31 AM Zongmin Zhou <zhouzongmin at kylinos.cn> wrote:
>
> Some boards(like RX550) seem to have garbage in the upper
> 16 bits of the vram size register.  Check for
> this and clamp the size properly.  Fixes
> boards reporting bogus amounts of vram.
>
> after add this patch,the maximum GPU VRAM size is 64GB,
> otherwise only 64GB vram size will be used.

Can you provide some examples of problematic boards and possibly a
vbios image from the problematic board?  What values are you seeing?
It would be nice to see what the boards are reporting and whether the
lower 16 bits are actually correct or if it is some other issue.  This
register is undefined until the asic has been initialized.  The vbios
programs it as part of it's asic init sequence (either via vesa/gop or
the OS driver).

Alex


>
> Signed-off-by: Zongmin Zhou<zhouzongmin at kylinos.cn>
> ---
>  drivers/gpu/drm/amd/amdgpu/gmc_v8_0.c | 13 ++++++++++---
>  1 file changed, 10 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/gmc_v8_0.c b/drivers/gpu/drm/amd/amdgpu/gmc_v8_0.c
> index 492ebed2915b..63b890f1e8af 100644
> --- a/drivers/gpu/drm/amd/amdgpu/gmc_v8_0.c
> +++ b/drivers/gpu/drm/amd/amdgpu/gmc_v8_0.c
> @@ -515,10 +515,10 @@ static void gmc_v8_0_mc_program(struct amdgpu_device *adev)
>  static int gmc_v8_0_mc_init(struct amdgpu_device *adev)
>  {
>         int r;
> +       u32 tmp;
>
>         adev->gmc.vram_width = amdgpu_atombios_get_vram_width(adev);
>         if (!adev->gmc.vram_width) {
> -               u32 tmp;
>                 int chansize, numchan;
>
>                 /* Get VRAM informations */
> @@ -562,8 +562,15 @@ static int gmc_v8_0_mc_init(struct amdgpu_device *adev)
>                 adev->gmc.vram_width = numchan * chansize;
>         }
>         /* size in MB on si */
> -       adev->gmc.mc_vram_size = RREG32(mmCONFIG_MEMSIZE) * 1024ULL * 1024ULL;
> -       adev->gmc.real_vram_size = RREG32(mmCONFIG_MEMSIZE) * 1024ULL * 1024ULL;
> +       tmp = RREG32(mmCONFIG_MEMSIZE);
> +       /* some boards may have garbage in the upper 16 bits */
> +       if (tmp & 0xffff0000) {
> +               DRM_INFO("Probable bad vram size: 0x%08x\n", tmp);
> +               if (tmp & 0xffff)
> +                       tmp &= 0xffff;
> +       }
> +       adev->gmc.mc_vram_size = tmp * 1024ULL * 1024ULL;
> +       adev->gmc.real_vram_size = adev->gmc.mc_vram_size;
>
>         if (!(adev->flags & AMD_IS_APU)) {
>                 r = amdgpu_device_resize_fb_bar(adev);
> --
> 2.25.1
>
>
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