[PATCH v2 1/5] drm: add legacy support for using degamma for gamma

[Tomi Valkeinen]

On 30/11/2020 12:38, Laurent Pinchart wrote:

>> + * can be used when the driver exposes either only GAMMA_LUT or both GAMMA_LUT
>> + * and DEGAMMA_LUT.
>> + */
>> +int drm_atomic_helper_legacy_gamma_set(struct drm_crtc *crtc,
>> +				       u16 *red, u16 *green, u16 *blue,
>> +				       uint32_t size,
>> +				       struct drm_modeset_acquire_ctx *ctx)
>> +{
>> +	return legacy_gamma_degamma_set(crtc, red, green, blue, size, ctx, false);
>> +}
> 
> I wonder, would it make sense to make this automatic by setting the
> degamma LUT when only the DEGAMMA_LUT property exists, and the gamma LUT
> otherwise ? Are there use cases for drm_atomic_helper_legacy_degamma_set
> for drivers that support both gamma and degamma ?

Yes, I think drm_atomic_helper_legacy_gamma_set() could do that.

But if you look at the second patch, the driver deals with crtc_state->degamma_lut. Having
.gamma_set = drm_atomic_helper_legacy_degamma_set makes it bit more explicit and clear what the
driver is doing.

That said, documenting what drm_atomic_helper_legacy_gamma_set does if there's only degamma should
also be clear enough, so... I don't have strong feelings either way =).

 Tomi

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