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: <98b43276-2a68-4ba9-999a-c738b8f7654f@ideasonboard.com>
Date: Thu, 5 Dec 2024 18:08:24 +0200
From: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
To: Geert Uytterhoeven <geert@...ux-m68k.org>
Cc: Laurent Pinchart <laurent.pinchart@...asonboard.com>,
 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,
 Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>,
 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

Hi,

On 05/12/2024 16:16, Geert Uytterhoeven wrote:
> Hi Tomi,
> 
> CC Jacopo
> 
> On Thu, Dec 5, 2024 at 2:45 PM Tomi Valkeinen
> <tomi.valkeinen@...asonboard.com> 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...

  Tomi