Re: [PATCH 1/4] drm/amd/display: Adjust plane init for off by one error

[Mario Limonciello <superm1@kernel.org>]

On 1/21/25 10:32, Harry Wentland wrote:
> 
> 
> On 2025-01-21 08:57, Mario Limonciello wrote:
>> From: Mario Limonciello <mario.limonciello@amd.com>
>>
>> The number of active surfaces is initialized to the number
>> of active planes.  If the number of planes aren't initialized
>> properly then the last plane can end up not getting initialized
>> which can be a divide by zero error.
>>
>> Reported-and-tested-by: Luke Jones <luke@ljones.dev>
>> Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/3794
>> Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/3533
>> Fixes: 7966f319c66d9 ("drm/amd/display: Introduce DML2")
>> Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
>> ---
>>   drivers/gpu/drm/amd/display/dc/dml2/display_mode_core.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/amd/display/dc/dml2/display_mode_core.c b/drivers/gpu/drm/amd/display/dc/dml2/display_mode_core.c
>> index 8dabb1ac0b684..45147b812d7d9 100644
>> --- a/drivers/gpu/drm/amd/display/dc/dml2/display_mode_core.c
>> +++ b/drivers/gpu/drm/amd/display/dc/dml2/display_mode_core.c
>> @@ -6787,7 +6787,7 @@ dml_bool_t dml_core_mode_support(struct display_mode_lib_st *mode_lib)
>>   		}
>>   	}
>>   
>> -	for (k = 0; k <= mode_lib->ms.num_active_planes - 1; k++) {
>> +	for (k = 0; k <= mode_lib->ms.num_active_planes; k++) {
> 
> Shouldn't this be either
> 	k <= num_active_planes -1
> or
> 	k < num_active_planes
> ?
> 
> Is num_active_planes wrong somehow?

Oh I see your point, that /should/ be the right value then for this 
particular loop and the rest of the corrections don't make sense either.

I'm not sure where the issue actually is then.

> 
> Harry
> 
>>   		CalculateBytePerPixelAndBlockSizes(
>>   								mode_lib->ms.cache_display_cfg.surface.SourcePixelFormat[k],
>>   								mode_lib->ms.cache_display_cfg.surface.SurfaceTiling[k],
>