[PATCH] drm/i915/intel_crtc: Warn and clamp if num_scalers exceeds SKL_NUM_SCALERS

[Jani Nikula]

On Thu, 07 Aug 2025, Jani Nikula <jani.nikula at linux.intel.com> wrote:
> On Thu, 07 Aug 2025, Ankit Nautiyal <ankit.k.nautiyal at intel.com> wrote:
>> Add a drm_WARN_ON() in intel_crtc_init() to catch cases where
>> crtc->num_scalers exceeds the expected SKL_NUM_SCALERS limit.
>>
>> This condition should not occur, as the number of scalers per pipe does not
>> exceed two for current platforms, making SKL_NUM_SCALERS (2) a safer upper
>> limit. However, if a platform ever gains more scalers per pipe than
>> SKL_NUM_SCALERS, it could lead to issues when crtc->num_scalers is used to
>> iterate over scaler_state->scalers.
>>
>> To prevent this, warn and clamp the value to SKL_NUM_SCALERS.
>>
>> Suggested-by: Jani Nikula <jani.nikula at intel.com>
>> Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal at intel.com>
>
> Reviewed-by: Jani Nikula <jani.nikula at intel.com>

PS. This could've been in __intel_display_device_info_runtime_init()
too, but no big deal.

>
>> ---
>>  drivers/gpu/drm/i915/display/intel_crtc.c | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/i915/display/intel_crtc.c b/drivers/gpu/drm/i915/display/intel_crtc.c
>> index a187db6df2d3..e262e686dc2b 100644
>> --- a/drivers/gpu/drm/i915/display/intel_crtc.c
>> +++ b/drivers/gpu/drm/i915/display/intel_crtc.c
>> @@ -317,6 +317,9 @@ int intel_crtc_init(struct intel_display *display, enum pipe pipe)
>>  	crtc->pipe = pipe;
>>  	crtc->num_scalers = DISPLAY_RUNTIME_INFO(display)->num_scalers[pipe];
>>  
>> +	if (drm_WARN_ON(display->drm, crtc->num_scalers > SKL_NUM_SCALERS))
>> +		crtc->num_scalers = SKL_NUM_SCALERS;
>> +
>>  	if (DISPLAY_VER(display) >= 9)
>>  		primary = skl_universal_plane_create(display, pipe, PLANE_1);
>>  	else

-- 
Jani Nikula, Intel