Hi Laurent, Thanks for the feedback. > Subject: Re: [PATCH] drm: rcar-du: Add setting to PnALPHAR register on > Gen3 > > Hi Biju, > > Thank you for the patch. > > On Sat, Apr 23, 2022 at 08:37:28AM +0100, Biju Das wrote: > > 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] > > > > 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 > > + */ > > Comments should start with /* on a line of its own, and you can also > reflow the text to 80 columns: OK. > > /* > * In Gen3, PnALPHAR register need to be set to 0 to avoid black > screen > * issue when alpha blend is enable on DU module. > */ > > It would however be nicer to document the exact behaviour, but the latest > version of the documentation I have access to is rev 2.3 and it lists > PnALPHAR as not available on Gen3. I don't have access to rev 2.4, but I got access to "R-Car-Gen3_Common_OPC_Customer_Notifications_V30.1.pdf" where it is mentioned about this issue and solution for fix which is inline with the patch from R-Car BSP. "The reason is that a register is not initialized by reset. This could lead to output wrong image data of other plane or wrong color set from BPOR (Background plane output register)." > > Furthermore, is this really the right fix, shouldn't we instead avoid > enabling alpha-blending in PnMR on Gen3 ? Avoid enabling alpha-blending in PnMR on Gen3, will it help here? Here the issue they mentioned as "register is not initialized by reset" Cheers, Biju > > > + rcar_du_plane_write(rgrp, index, PnALPHAR, 0x00000000); > > } > > > > static void rcar_du_plane_setup_format(struct rcar_du_group *rgrp, > > -- > Regards, > > Laurent Pinchart
