When mgag200 switched from simple KMS to regular atomic helpers,
the initialization of the gamma settings was lost.
This leads to a black screen, if the bios/uefi doesn't use the same
pixel color depth.

v2: rebase on top of drm-misc-fixes, and add Cc stable tag.

Link: https://bugzilla.redhat.com/show_bug.cgi?id=2171155
Fixes: 1baf9127c482 ("drm/mgag200: Replace simple-KMS with regular atomic 
helpers")
Cc: <[email protected]>
Tested-by: Phil Oester <[email protected]>
Reviewed-by: Thomas Zimmermann <[email protected]>
Signed-off-by: Jocelyn Falempe <[email protected]>
---
 drivers/gpu/drm/mgag200/mgag200_mode.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/gpu/drm/mgag200/mgag200_mode.c 
b/drivers/gpu/drm/mgag200/mgag200_mode.c
index 0a5aaf78172a..576c4c838a33 100644
--- a/drivers/gpu/drm/mgag200/mgag200_mode.c
+++ b/drivers/gpu/drm/mgag200/mgag200_mode.c
@@ -640,6 +640,11 @@ void mgag200_crtc_helper_atomic_enable(struct drm_crtc 
*crtc, struct drm_atomic_
        if (funcs->pixpllc_atomic_update)
                funcs->pixpllc_atomic_update(crtc, old_state);
 
+       if (crtc_state->gamma_lut)
+               mgag200_crtc_set_gamma(mdev, format, 
crtc_state->gamma_lut->data);
+       else
+               mgag200_crtc_set_gamma_linear(mdev, format);
+
        mgag200_enable_display(mdev);
 
        if (funcs->enable_vidrst)

base-commit: a26cc2934331b57b5a7164bff344f0a2ec245fc0
-- 
2.39.2

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