VCN_INFO_TABLE_MAX_NUM_INSTANCES vs AMDGPU_MAX_VCN_INSTANCES

[Ernst Sjöstrand]

Looks good to me!

Den mån 16 maj 2022 kl 20:15 skrev Alex Deucher <alexdeucher at gmail.com>:

> On Mon, May 16, 2022 at 2:10 PM Christian König
> <ckoenig.leichtzumerken at gmail.com> wrote:
> >
> > Am 16.05.22 um 19:49 schrieb Ernst Sjöstrand:
> >
> > Den mån 16 maj 2022 kl 17:13 skrev Alex Deucher <alexdeucher at gmail.com>:
> >>
> >> On Sun, May 15, 2022 at 11:46 AM Ernst Sjöstrand <ernstp at gmail.com>
> wrote:
> >> >
> >> > smatch found this problem on amd-staging-drm-next:
> >> >
> >> > drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c:1443
> amdgpu_discovery_get_vcn_info() error: buffer overflow
> 'adev->vcn.vcn_codec_disable_mask' 2 <= 3
> >> >
> >> > This is caused by:
> >> > #define AMDGPU_MAX_VCN_INSTANCES 2
> >> > #define VCN_INFO_TABLE_MAX_NUM_INSTANCES 4
> >> >
> >> > Can we just drop VCN_INFO_TABLE_MAX_NUM_INSTANCES completely and use
> AMDGPU_MAX_VCN_INSTANCES everywhere instead (and bump it to 4)?
> >>
> >> We should be able to bump AMDGPU_MAX_VCN_INSTANCES to 4 (although it
> >> would waste some memory in the places it is used at this point).
> >> VCN_INFO_TABLE_MAX_NUM_INSTANCES is part of a firmware structure so we
> >> can't change that without breaking the firmware structure.
> >>
> >> Alex
> >
> >
> > It would be nice to get rid of this pattern and make sure it doesn't
> happen again when the VCN info table is raised to 5.
> > It's very similar to the HWIP_MAX_INSTANCE issue.
> >
> >
> > No, as Alex explained that distinction is intentional.
> >
> > The firmware definition is 4 for future extensions, that doesn't mean
> that this is currently used.
> >
> > There is currently simply no need to set AMDGPU_MAX_VCN_INSTANCES to
> more than 2.
>
> Right.  The attached patch should protect against the scenario you are
> envisioning.
>
> Alex
>
> >
> > Regards,
> > Christian.
> >
> >
> > //E
> >
> >
>
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