linux-kernel - Re: [PATCH v3 02/10] drm/rcar-du: Write DPTSR only if the second source exists

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Message-ID: <20241209230418.GC26531@pendragon.ideasonboard.com>
Date: Tue, 10 Dec 2024 01:04:18 +0200
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
Cc: 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>
Subject: Re: [PATCH v3 02/10] drm/rcar-du: Write DPTSR only if the second
 source exists

Hi Tomi,

Thank you for the patch.

On Fri, Dec 06, 2024 at 11:32:35AM +0200, Tomi Valkeinen wrote:
> From: Tomi Valkeinen <tomi.valkeinen+renesas@...asonboard.com>
> 
> Currently the driver always writes DPTSR when setting up the hardware.
> However, writing the register is only meaningful when the second source
> for a plane is used, and the register is not even documented for SoCs
> that do not have the second source.

I've confirmed that for all the models currently supported by the DU
driver.

> So move the write behind a condition.
> 
> Signed-off-by: Tomi Valkeinen <tomi.valkeinen+renesas@...asonboard.com>

Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>

I will test the series on an M3N board.

> ---
>  drivers/gpu/drm/renesas/rcar-du/rcar_du_group.c | 20 +++++++++++++++-----
>  1 file changed, 15 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..1ec806c8e013 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 +185,21 @@ 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);
> +	/*
> +	 * DPTSR is used to select the source for the planes of a group. The
> +	 * first source is chosen by writing 0 to the respective bits, and this
> +	 * is always the default value of the register. In other words, writing
> +	 * DPTSR is only needed if the SoC supports choosing the second source.
> +	 *
> +	 * The SoCs documentations seems to confirm this, as the DPTSR register
> +	 * is not documented if only the first source exists on that SoC.
> +	 */
> +	if (rgrp->channels_mask & BIT(1)) {
> +		mutex_lock(&rgrp->lock);
> +		rcar_du_group_write(rgrp, DPTSR, (rgrp->dptsr_planes << 16) |
> +				    rgrp->dptsr_planes);
> +		mutex_unlock(&rgrp->lock);
> +	}
>  }
>  
>  /*
> 

-- 
Regards,

Laurent Pinchart