Re: [PATCH] drm: rcar-du: Re-update the DSYSR register value for start/stop

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hello Hoan,

On Tuesday, 23 October 2018 04:01:19 EET Hoan wrote:
> On 2018/10/22 20:23, Laurent Pinchart wrote:
> > On Monday, 22 October 2018 09:30:54 EEST Nguyen An Hoan wrote:
> >> From: Hoan Nguyen An <na-hoan@jinso.co.jp>
> >> 
> >>  From previous commit 0521ccb "drm: rcar-du: Cache DSYSR value to ensure
> >> 
> >> known initial value"
> > 
> > What exact commit are you referring to ? The mainline commit that has this
> > subject is 9144adc5e5a99577bce0d4ee2ca3615f53b9d296.
> 
> Seems I have cited the wrong Commit-ID、it is
> 
> 9144adc5e5a99577bce0d4ee2ca3615f53b9d296
> drm: rcar-du: Cache DSYSR value to ensure known initial value
> 
> >> We only need to update DSYSR0, DSYSR2 for start/stop.
> >> So using rgrp-> mmio_offset is enough, the change back from rcar_du_crtc
> >> ->rcar_du_group -> rcar_du_crtc leading to mmio addresses for DSYSR may
> >> be different.
> > 
> > Is this fixing an actual problem ? If you look at the code, the line
> > 
> > 	struct rcar_du_crtc *rcrtc = &rgrp->dev->crtcs[rgrp->index * 2];
> > 
> > makes sure that we select DU0 or DU2 only, so the register write
> > 
> > 	rcar_du_crtc_dsysr_clr_set(rcrtc, DSYSR_DRES | DSYSR_DEN,
> > 				   start ? DSYSR_DEN : DSYSR_DRES);
> > 
> > should only access DSYSR0 and DSYSR2.
> 
> This seems I think to fix the rcar-du problem with M3N-r8a77965,
> 
> With M3N-R8a77965 we have DU0, DU1, DU3
> So, when Laurent-san divide objetcs into rcar_du_group, rcar_du_crtc.
> 
> DU0, DU1 -> du_group[0]  rgrp-> mmio_offset = DU0_REG_OFFSET
> DU3->du_group[1] and rgrp-> mmio_offset = DU2_REG_OFFSET, but 
> rcrtc->mmio_offset=DU3_REG_OFFSET (with M3N)
> 
> M3N-R8a77965 not have DU2, So after the command:
> 
> struct rcar_du_crtc *rcrtc = &rgrp->dev->crtcs[rgrp->index * 2];
> 
> So in fact, with M3N we are updating DSYSR3 (In this my TC, this
> reference to start/stop DU3-RGB)
> 
> This will not affect H3, since the H3 lines always have enough DU0,
> DU1,DU2,DU3.

You're absolutely right. I'm sorry for introducing the bug in the first place, 
and for failing to understand your patch.

I would however prefer a different fix, as switching back to 
rcar_du_group_write() defeats the purpose of the "drm: rcar-du: Cache DSYSR 
value to ensure known initial value" patch. I will submit a patch and CC you.

-- 
Regards,

Laurent Pinchart