linux-kernel - Re: [PATCH v2 02/10] drm/rcar-du: Write DPTSR only if there are more than one crtc

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Message-ID: <20241205173452.GA21014@pendragon.ideasonboard.com>
Date: Thu, 5 Dec 2024 19:34:52 +0200
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
Cc: Geert Uytterhoeven <geert@...ux-m68k.org>,
	Kieran Bingham <kieran.bingham+renesas@...asonboard.com>,
	Andrzej Hajda <andrzej.hajda@...el.com>,
	Neil Armstrong <neil.armstrong@...aro.org>,
	Robert Foss <rfoss@...nel.org>, Jonas Karlman <jonas@...boo.se>,
	Jernej Skrabec <jernej.skrabec@...il.com>,
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Geert Uytterhoeven <geert+renesas@...der.be>,
	Magnus Damm <magnus.damm@...il.com>,
	Michael Turquette <mturquette@...libre.com>,
	Stephen Boyd <sboyd@...nel.org>, LUU HOAI <hoai.luu.ub@...esas.com>,
	Jagan Teki <jagan@...rulasolutions.com>,
	Sam Ravnborg <sam@...nborg.org>,
	Biju Das <biju.das.jz@...renesas.com>,
	dri-devel@...ts.freedesktop.org, linux-renesas-soc@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-clk@...r.kernel.org,
	Tomi Valkeinen <tomi.valkeinen+renesas@...asonboard.com>,
	Jacopo Mondi <jacopo.mondi@...asonboard.com>
Subject: Re: [PATCH v2 02/10] drm/rcar-du: Write DPTSR only if there are more
 than one crtc

On Thu, Dec 05, 2024 at 06:08:24PM +0200, Tomi Valkeinen wrote:
> On 05/12/2024 16:16, Geert Uytterhoeven wrote:
> > Hi Tomi,
> > 
> > CC Jacopo
> > 
> > On Thu, Dec 5, 2024 at 2:45 PM Tomi Valkeinen wrote:
> >> From: Tomi Valkeinen <tomi.valkeinen+renesas@...asonboard.com>
> >>
> >> Currently the driver always writes DPTSR when setting up the hardware.
> >> However, the register is only meaningful when there are more than one
> >> crtc, and the only SoC with one crtc, V3M, does not have the register
> >> mentioned in its documentation.
> > 
> > R-Car V3H/V3H_2, too.
> 
> Right... I was looking at the number of outputs, not the number of crtcs 
> when going through the SoCs.
> 
> >> So move the write behind a condition.
> >>
> >> Signed-off-by: Tomi Valkeinen <tomi.valkeinen+renesas@...asonboard.com>
> >> ---
> >>   drivers/gpu/drm/renesas/rcar-du/rcar_du_group.c | 12 +++++++-----
> >>   1 file changed, 7 insertions(+), 5 deletions(-)
> >>
> >> diff --git a/drivers/gpu/drm/renesas/rcar-du/rcar_du_group.c b/drivers/gpu/drm/renesas/rcar-du/rcar_du_group.c
> >> index 2ccd2581f544..0fbf6abbde6e 100644
> >> --- a/drivers/gpu/drm/renesas/rcar-du/rcar_du_group.c
> >> +++ b/drivers/gpu/drm/renesas/rcar-du/rcar_du_group.c
> >> @@ -185,11 +185,13 @@ static void rcar_du_group_setup(struct rcar_du_group *rgrp)
> >>                  dorcr |= DORCR_PG1T | DORCR_DK1S | DORCR_PG1D_DS1;
> >>          rcar_du_group_write(rgrp, DORCR, dorcr);
> >>
> >> -       /* Apply planes to CRTCs association. */
> >> -       mutex_lock(&rgrp->lock);
> >> -       rcar_du_group_write(rgrp, DPTSR, (rgrp->dptsr_planes << 16) |
> >> -                           rgrp->dptsr_planes);
> >> -       mutex_unlock(&rgrp->lock);
> >> +       if (rgrp->num_crtcs > 1) {
> >> +               /* Apply planes to CRTCs association. */
> >> +               mutex_lock(&rgrp->lock);
> >> +               rcar_du_group_write(rgrp, DPTSR, (rgrp->dptsr_planes << 16) |
> >> +                                   rgrp->dptsr_planes);
> >> +               mutex_unlock(&rgrp->lock);
> >> +       }
> > 
> > This is per group, not per DU, right?
> > The second group on R-Car M3-W/M3-W+ has a single channel, hence no
> > DPTSR2 register.
> > The second group on R-Car M3-N has a single channel, but it's actually
> > the second physical channel in the group, and thus does have DPTSR2.
> 
> That logic does make sense. So that would be if (rgrp->channels_mask & 
> BIT(1)) then write DPTSR? And probably add a comment in the code about this.
> 
> > And apparently we had this discussion before...
> > https://lore.kernel.org/all/CAMuHMdXxf4oePnyLvp84OhSa+wdehCNJBXnhjYO7-1VxpBJ7eQ@mail.gmail.com
> 
> Somehow I hadn't even realized Jacopo had sent these before...

Oops...

I'll let Jacopo and you decide who will send an updated patch.

-- 
Regards,

Laurent Pinchart