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

[Melissa Wen]

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.

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,
-- 
2.47.2