linux-kernel - Re: [PATCH v2] drm/rcar-du: dsi: Handle both DRM_MODE_FLAG_N.SYNC and !DRM_MODE_FLAG

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Message-ID: <20251203022430.GK8219@pendragon.ideasonboard.com>
Date: Wed, 3 Dec 2025 11:24:30 +0900
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 v2] drm/rcar-du: dsi: Handle both DRM_MODE_FLAG_N.SYNC
 and !DRM_MODE_FLAG_P.SYNC

Hi Marek,

Thank you for the patch.

On Tue, Dec 02, 2025 at 07:11:06PM +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. The previous behavior
> was to assume that neither flag means DRM_MODE_FLAG_N.SYNC . Restore the
> previous behavior for maximum compatibility.
> 
> The change of behavior is visible below, consider Vertical mode->flags
> for simplicity sake, although the same applies to Horizontal ones:
> 
> Before 94fe479fae96 ("drm/rcar-du: dsi: Clean up handling of DRM mode flags") :
> 
> - DRM_MODE_FLAG_PVSYNC => vprmset0r |= 0
> - DRM_MODE_FLAG_NVSYNC => vprmset0r |= TXVMVPRMSET0R_VSPOL_LOW
> - Neither DRM_MODE_FLAG_[PN]VSYNC => vprmset0r |= TXVMVPRMSET0R_VSPOL_LOW
> 
> After 94fe479fae96 ("drm/rcar-du: dsi: Clean up handling of DRM mode flags") :
> 
> - DRM_MODE_FLAG_PVSYNC => vprmset0r |= 0
> - DRM_MODE_FLAG_NVSYNC => vprmset0r |= TXVMVPRMSET0R_VSPOL_LOW
> - Neither DRM_MODE_FLAG_[PN]VSYNC => vprmset0r |= 0 <---------- This broke
> 
> The "Neither" case behavior is different, because DRM_MODE_FLAG_N[HV]SYNC is
> really not equivalent !DRM_MODE_FLAG_P[HV]SYNC .
> 
> Fixes: 94fe479fae96 ("drm/rcar-du: dsi: Clean up handling of DRM mode flags")
> Signed-off-by: Marek Vasut <marek.vasut+renesas@...lbox.org>

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

> ---
> 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
> ---
> V2: - Update commit message
>     - Use only !P[HV]SYNC
> ---
>  drivers/gpu/drm/renesas/rcar-du/rcar_mipi_dsi.c | 4 ++--
>  1 file changed, 2 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..4ef2e3c129ed7 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 +492,9 @@ 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_PVSYNC))
>  		vprmset0r |= TXVMVPRMSET0R_VSPOL_LOW;
> -	if (mode->flags & DRM_MODE_FLAG_NHSYNC)
> +	if (!(mode->flags & DRM_MODE_FLAG_PHSYNC))
>  		vprmset0r |= TXVMVPRMSET0R_HSPOL_LOW;
>  
>  	vprmset1r = TXVMVPRMSET1R_VACTIVE(mode->vdisplay)

-- 
Regards,

Laurent Pinchart