From: LUU HOAI <hoai.luu.ub@xxxxxxxxxxx> In Gen3, when Alpha blend is enabled in the PnMR register, depending on the initial value of the PnALPHAR register, either channel of DU might be black screen. Therefore, this patch prevents the black screen by setting the PnALPHAR register to all 0. In addition, PnALPHAR register will be released in the R-Car Gen3 Hardware Manual Rev 2.4 (Sep. 2021). Signed-off-by: LUU HOAI <hoai.luu.ub@xxxxxxxxxxx> Signed-off-by: Biju Das <biju.das.jz@xxxxxxxxxxxxxx> --- This patch is based on [1] [1] https://github.com/renesas-rcar/linux-bsp/commit/fcb34fe338cbde0a64919430733541035f20a784 Not sure this patches has to go with Fixes tag for stable?? Tested the changes on RZ/G2M board root@hihope-rzg2m:/cip-test-scripts# modetest -M rcar-du -w 54:alpha:55555 root@hihope-rzg2m:/cip-test-scripts# modetest -M rcar-du -s "93@90:1024x768@AR24" -d -P "54@90:400x300+200+200@XR24" setting mode 1024x768-75Hz@AR24 on connectors 93, crtc 90 testing 400x300@XR24 overlay plane 54 --- drivers/gpu/drm/rcar-du/rcar_du_plane.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/drivers/gpu/drm/rcar-du/rcar_du_plane.c b/drivers/gpu/drm/rcar-du/rcar_du_plane.c index 5c1c7bb04f3f..aff39b9253f8 100644 --- a/drivers/gpu/drm/rcar-du/rcar_du_plane.c +++ b/drivers/gpu/drm/rcar-du/rcar_du_plane.c @@ -510,6 +510,12 @@ static void rcar_du_plane_setup_format_gen3(struct rcar_du_group *rgrp, rcar_du_plane_write(rgrp, index, PnDDCR4, state->format->edf | PnDDCR4_CODE); + + /* In Gen3, PnALPHAR register need to be set to 0 + * to avoid black screen issue when alpha blend is enable + * on DU module + */ + rcar_du_plane_write(rgrp, index, PnALPHAR, 0x00000000); } static void rcar_du_plane_setup_format(struct rcar_du_group *rgrp, -- 2.25.1
