linux-kernel - Re: [PATCH] drm/rcar-du: dsi: Handle both DRM_MODE_FLAG_N.SYNC and !DRM_MODE_FLAG

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Message-ID: <20251107232329.GI5558@pendragon.ideasonboard.com>
Date: Sat, 8 Nov 2025 01:23:29 +0200
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Marek Vasut <marek.vasut+renesas@...lbox.org>
Cc: dri-devel@...ts.freedesktop.org, David Airlie <airlied@...il.com>,
	Geert Uytterhoeven <geert+renesas@...der.be>,
	Kieran Bingham <kieran.bingham+renesas@...asonboard.com>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Magnus Damm <magnus.damm@...il.com>,
	Maxime Ripard <mripard@...nel.org>, Simona Vetter <simona@...ll.ch>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	Tomi Valkeinen <tomi.valkeinen+renesas@...asonboard.com>,
	linux-kernel@...r.kernel.org, linux-renesas-soc@...r.kernel.org
Subject: Re: [PATCH] drm/rcar-du: dsi: Handle both DRM_MODE_FLAG_N.SYNC and
 !DRM_MODE_FLAG_P.SYNC

On Sat, Nov 08, 2025 at 12:04:10AM +0100, Marek Vasut wrote:
> Since commit 94fe479fae96 ("drm/rcar-du: dsi: Clean up handling of DRM mode flags")
> the driver does not set TXVMVPRMSET0R_VSPOL_LOW and TXVMVPRMSET0R_HSPOL_LOW
> for modes which set neither DRM_MODE_FLAG_[PN].SYNC.

Could you please explain what broke ? What panel are you using ?

> The previous behavior
> was to assume that neither flag means DRM_MODE_FLAG_N.SYNC . Restore the
> previous behavior for maximum compatibility.
> 
> Fixes: 94fe479fae96 ("drm/rcar-du: dsi: Clean up handling of DRM mode flags")
> Signed-off-by: Marek Vasut <marek.vasut+renesas@...lbox.org>
> ---
> Cc: David Airlie <airlied@...il.com>
> Cc: Geert Uytterhoeven <geert+renesas@...der.be>
> Cc: Kieran Bingham <kieran.bingham+renesas@...asonboard.com>
> Cc: Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>
> Cc: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>
> Cc: Magnus Damm <magnus.damm@...il.com>
> Cc: Maxime Ripard <mripard@...nel.org>
> Cc: Simona Vetter <simona@...ll.ch>
> Cc: Thomas Zimmermann <tzimmermann@...e.de>
> Cc: Tomi Valkeinen <tomi.valkeinen+renesas@...asonboard.com>
> Cc: dri-devel@...ts.freedesktop.org
> Cc: linux-kernel@...r.kernel.org
> Cc: linux-renesas-soc@...r.kernel.org
> ---
>  drivers/gpu/drm/renesas/rcar-du/rcar_mipi_dsi.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/renesas/rcar-du/rcar_mipi_dsi.c b/drivers/gpu/drm/renesas/rcar-du/rcar_mipi_dsi.c
> index 9413b76d0bfce..98bd7f40adbea 100644
> --- a/drivers/gpu/drm/renesas/rcar-du/rcar_mipi_dsi.c
> +++ b/drivers/gpu/drm/renesas/rcar-du/rcar_mipi_dsi.c
> @@ -492,9 +492,11 @@ static void rcar_mipi_dsi_set_display_timing(struct rcar_mipi_dsi *dsi,
>  
>  	/* Configuration for Video Parameters, input is always RGB888 */
>  	vprmset0r = TXVMVPRMSET0R_BPP_24;
> -	if (mode->flags & DRM_MODE_FLAG_NVSYNC)
> +	if ((mode->flags & DRM_MODE_FLAG_NVSYNC) ||
> +	    !(mode->flags & DRM_MODE_FLAG_PVSYNC))
>  		vprmset0r |= TXVMVPRMSET0R_VSPOL_LOW;

I don't think this restores the previous behaviour. You would need to
write

	if (!(mode->flags & DRM_MODE_FLAG_PVSYNC))
		vprmset0r |= TXVMVPRMSET0R_VSPOL_LOW;

> -	if (mode->flags & DRM_MODE_FLAG_NHSYNC)
> +	if ((mode->flags & DRM_MODE_FLAG_NHSYNC) ||
> +	    !(mode->flags & DRM_MODE_FLAG_PHSYNC))
>  		vprmset0r |= TXVMVPRMSET0R_HSPOL_LOW;

Same here.

>  
>  	vprmset1r = TXVMVPRMSET1R_VACTIVE(mode->vdisplay)

-- 
Regards,

Laurent Pinchart