[PATCH RFC 5/6] drm/amdgpu: don't wake up the GPU for mmGB_ADDR_CONFIG register read

[Philipp Zabel]

On Thu, Jul 31, 2025 at 9:38 PM Alex Deucher <alexdeucher at gmail.com> wrote:

> On Thu, Jul 31, 2025 at 3:33 AM Philipp Zabel <philipp.zabel at gmail.com>
> wrote:
> >
> > Don't wake the GPU if libdrm queries the mmGB_ADDR_CONFIG register
> > value during amdgpu_query_gpu_info_init(). Instead, return the already
> > cached value adev->gfx.config.gb_addr_config.
> >
> > Link: https://gitlab.freedesktop.org/drm/amd/-/issues/2295
> > Signed-off-by: Philipp Zabel <philipp.zabel at gmail.com>
> > ---
> >  drivers/gpu/drm/amd/amdgpu/amdgpu_kms.c | 10 ++++++++++
> >  1 file changed, 10 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_kms.c
> b/drivers/gpu/drm/amd/amdgpu/amdgpu_kms.c
> > index fe1347a4075c4..ed4d7d72f2065 100644
> > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_kms.c
> > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_kms.c
> > @@ -883,6 +883,16 @@ int amdgpu_info_ioctl(struct drm_device *dev, void
> *data, struct drm_file *filp)
> >
> >                 alloc_size = info->read_mmr_reg.count * sizeof(*regs);
> >
> > +               if (info->read_mmr_reg.dword_offset == 0x263e &&
>
> I think the offset of this register varies across chip families.
> You'll need some way to determine what the offset is for each family.
>

Thank you. This workaround was specifically intended for the following call
in libdrm [1]:

        r = amdgpu_read_mm_registers(dev, 0x263e, 1, 0xffffffff, 0,
                                             &dev->info.gb_addr_cfg);

[1]
https://gitlab.freedesktop.org/mesa/libdrm/-/blob/9ea8a8e93d542fe61d82716d1a721e8d1d257405/amdgpu/amdgpu_gpu_info.c#L215-216

which also seem to hard-code the dword_offset?

The same is now copied into Mesa [2] as:

   r = ac_drm_read_mm_registers(dev, 0x263e, 1, 0xffffffff, 0,
&info->gb_addr_cfg);

[2]
https://gitlab.freedesktop.org/mesa/mesa/-/blob/c64c6a0c31f9cb1339bc700d236932171f7444a3/src/amd/common/ac_linux_drm.c#L722

regards
Philipp
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