[PATCH] Revert "drm/amd/display: Hardware cursor changes color when switched to software cursor"

[Melissa Wen]

On 24/04/2025 16:10, Harry Wentland wrote:
>
> On 2025-04-22 10:58, Melissa Wen wrote:
>> This reverts commit 272e6aab14bbf98d7a06b2b1cd6308a02d4a10a1.
>>
>> Applying degamma curve to the cursor by default breaks Linux userspace
>> expectation.
>>
>> On Linux, AMD display manager enables cursor degamma ROM just for
>> implict sRGB on HW versions where degamma is split into two blocks:
>> degamma ROM for pre-defined TFs and `gamma correction` for user/custom
>> curves, and degamma ROM settings doesn't apply to cursor plane.
>>
>> Link: https://gitlab.freedesktop.org/drm/amd/-/issues/1513
>> Link: https://gitlab.freedesktop.org/drm/amd/-/issues/2803
>> Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/4144
>> Reported-by: Michel Dänzer <michel.daenzer at mailbox.org>
>> Signed-off-by: Melissa Wen <mwen at igalia.com>
>> ---
>>
>> Hi,
>>
>> I suspect there is a conflict of interest between OSes here, because
>> this is not the first time this mechanism has been removed from the
>> DC shared-code and after reintroduced [1].
>>
>> I'd suggest that other OSes set the `dc_cursor_attributes
>> attribute_flags.bits.ENABLE_CURSOR_DEGAMMA` to true by default, rather
>> than removing the mechanism that is valid for the Linux driver. Similar
>> to what the Linux AMD DM does for the implicit sRGB [2][3], but in their
>> case, they just need to initialize with 1.
>>
> That's a good suggestion and I started that conversation with
> Windows devs.
>
> Is there an IGT test that would test for this behavior? Without
> an IGT test I think we're apt to end back here again at some
> point.
Indeed, it's a good idea. AFAIK, there is no IGT color test for cursor.
I'll work on it then, as it might save everyone time.

Thanks

Melissa
>
> Harry
>
>> Finally, thanks Michel for pointing this issue out to me and noticing
>> the similarity to previous solution.
>>
>> [1] https://gitlab.freedesktop.org/agd5f/linux/-/commit/d9fbd64e8e317
>> [2] https://gitlab.freedesktop.org/agd5f/linux/-/commit/857b835f
>> [3] https://gitlab.freedesktop.org/agd5f/linux/-/commit/66eba12a
>>
>> Best Regards,
>>
>> Melissa
>>
>>   drivers/gpu/drm/amd/display/dc/dpp/dcn401/dcn401_dpp_cm.c | 5 +++--
>>   1 file changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/amd/display/dc/dpp/dcn401/dcn401_dpp_cm.c b/drivers/gpu/drm/amd/display/dc/dpp/dcn401/dcn401_dpp_cm.c
>> index 1236e0f9a256..712aff7e17f7 100644
>> --- a/drivers/gpu/drm/amd/display/dc/dpp/dcn401/dcn401_dpp_cm.c
>> +++ b/drivers/gpu/drm/amd/display/dc/dpp/dcn401/dcn401_dpp_cm.c
>> @@ -120,10 +120,11 @@ void dpp401_set_cursor_attributes(
>>   	enum dc_cursor_color_format color_format = cursor_attributes->color_format;
>>   	int cur_rom_en = 0;
>>   
>> -	// DCN4 should always do Cursor degamma for Cursor Color modes
>>   	if (color_format == CURSOR_MODE_COLOR_PRE_MULTIPLIED_ALPHA ||
>>   		color_format == CURSOR_MODE_COLOR_UN_PRE_MULTIPLIED_ALPHA) {
>> -		cur_rom_en = 1;
>> +		if (cursor_attributes->attribute_flags.bits.ENABLE_CURSOR_DEGAMMA) {
>> +			cur_rom_en = 1;
>> +		}
>>   	}
>>   
>>   	REG_UPDATE_3(CURSOR0_CONTROL,