[PATCH] drm/amd/display: Align num_crtc to max_streams

[Harry Wentland]

On 2/7/23 09:41, Hamza Mahfooz wrote:
> 
> On 2/7/23 09:31, Harry Wentland wrote:
>>
>>
>> On 2/7/23 08:00, Hamza Mahfooz wrote:
>>>
>>> On 2/6/23 23:05, Tianci Yin wrote:
>>>> From: tiancyin <tianci.yin at amd.com>
>>>>
>>>> [Why]
>>>> Display pipe might be harvested on some SKUs, that cause the
>>>> adev->mode_info.num_crtc mismatch with the usable crtc number,
>>>> then below error dmesgs observed after GPU recover.
>>>>
>>>>     *ERROR* amdgpu_dm_set_crtc_irq_state: crtc is NULL at id :3
>>>>     *ERROR* amdgpu_dm_set_crtc_irq_state: crtc is NULL at id :3
>>>>     *ERROR* amdgpu_dm_set_crtc_irq_state: crtc is NULL at id :3
>>>>     *ERROR* amdgpu_dm_set_pflip_irq_state: crtc is NULL at id :3
>>>>     *ERROR* amdgpu_dm_set_pflip_irq_state: crtc is NULL at id :3
>>>>     *ERROR* amdgpu_dm_set_pflip_irq_state: crtc is NULL at id :3
>>>>     *ERROR* amdgpu_dm_set_pflip_irq_state: crtc is NULL at id :3
>>>>     *ERROR* amdgpu_dm_set_vupdate_irq_state: crtc is NULL at id :3
>>>>     *ERROR* amdgpu_dm_set_vupdate_irq_state: crtc is NULL at id :3
>>>>     *ERROR* amdgpu_dm_set_vupdate_irq_state: crtc is NULL at id :3
>>>>
>>>> [How]
>>>> The max_streams is limited number after pipe fuse, align num_crtc
>>>> to max_streams to eliminate the error logs.
>>>>
>>>> Signed-off-by: tiancyin <tianci.yin at amd.com>
>>>> ---
>>>>    drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 3 +++
>>>>    1 file changed, 3 insertions(+)
>>>>
>>>> diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
>>>> index b31cfda30ff9..87ec2574cc09 100644
>>>> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
>>>> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
>>>> @@ -4285,6 +4285,9 @@ static int amdgpu_dm_initialize_drm_device(struct amdgpu_device *adev)
>>>>            break;
>>>>        }
>>>>    +    /* Adjust the crtc number according to the DCN pipe fuse. */
>>>> +    adev->mode_info.num_crtc = dm->dc->caps.max_streams;
>>>
>>> This would introduce array-out-bounds issues, since there are arrays of
>>> size AMDGPU_MAX_CRTCS that use num_crtc as a bounds check.
>>
>>  From what I can tell max_streams is always <= AMDGPU_MAX_CRTCS (6),
>> though we're not checking. Maybe it'd be good to check and print a
>> DRM_ERROR here if that's ever not the case (e.g., if we ever add
>> any new ASIC that has more streams).
> 
> I have had UBSAN warns before commit d633b7a25fbe ("drm/amd/display: fix
> possible buffer overflow relating to secure display") was applied, so it
> seems to already be the case, maybe due to virtual streams.
> 

Interesting.

On closer look I'm not sure why this patch is needed. We already
do exactly what this patch does at the beginning of
amdgpu_dm_initialize_drm_device:

> 	dm->display_indexes_num = dm->dc->caps.max_streams;
> 	/* Update the actual used number of crtc */
> 	adev->mode_info.num_crtc = adev->dm.display_indexes_num;

Harry

>>
>> Harry
>>
>>>
>>>> +
>>>>        for (i = 0; i < dm->dc->caps.max_streams; i++)
>>>>            if (amdgpu_dm_crtc_init(dm, mode_info->planes[i], i)) {
>>>>                DRM_ERROR("KMS: Failed to initialize crtc\n");
>>>
>>
>