linux-kernel - Re: [PATCH V2 2/2] drm/bridge: samsung-dsim: Fix porch calcalcuation rounding

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Message-ID: <6111fe04-4ecb-428e-9a0c-dc02cadfe3e7@denx.de>
Date: Sun, 21 Apr 2024 16:06:24 +0200
From: Marek Vasut <marex@...x.de>
To: Adam Ford <aford173@...il.com>, dri-devel@...ts.freedesktop.org
Cc: aford@...conembedded.com, Frieder Schrempf <frieder.schrempf@...tron.de>,
 Inki Dae <inki.dae@...sung.com>, Jagan Teki <jagan@...rulasolutions.com>,
 Marek Szyprowski <m.szyprowski@...sung.com>,
 Andrzej Hajda <andrzej.hajda@...el.com>,
 Neil Armstrong <neil.armstrong@...aro.org>, Robert Foss <rfoss@...nel.org>,
 Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
 Jonas Karlman <jonas@...boo.se>, Jernej Skrabec <jernej.skrabec@...il.com>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>,
 Marco Felsch <m.felsch@...gutronix.de>,
 Michael Tretter <m.tretter@...gutronix.de>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2 2/2] drm/bridge: samsung-dsim: Fix porch calcalcuation
 rounding

On 2/12/24 12:09 AM, Adam Ford wrote:
> When using video sync pulses, the HFP, HBP, and HSA are divided between
> the available lanes if there is more than one lane.  For certain
> timings and lane configurations, the HFP may not be evenly divisible.
> If the HFP is rounded down, it ends up being too small which can cause
> some monitors to not sync properly. In these instances, adjust htotal
> and hsync to round the HFP up, and recalculate the htotal.
> 
> Tested-by: Frieder Schrempf <frieder.schrempf@...tron.de> # Kontron BL i.MX8MM with HDMI monitor
> Signed-off-by: Adam Ford <aford173@...il.com>
> ---
> V2:  No changes
> 
> diff --git a/drivers/gpu/drm/bridge/samsung-dsim.c b/drivers/gpu/drm/bridge/samsung-dsim.c
> index 8476650c477c..52939211fe93 100644
> --- a/drivers/gpu/drm/bridge/samsung-dsim.c
> +++ b/drivers/gpu/drm/bridge/samsung-dsim.c
> @@ -1606,6 +1606,27 @@ static int samsung_dsim_atomic_check(struct drm_bridge *bridge,
>   		adjusted_mode->flags |= (DRM_MODE_FLAG_PHSYNC | DRM_MODE_FLAG_PVSYNC);
>   	}
>   
> +	/*
> +	 * When using video sync pulses, the HFP, HBP, and HSA are divided between
> +	 * the available lanes if there is more than one lane.  For certain
> +	 * timings and lane configurations, the HFP may not be evenly divisible.
> +	 * If the HFP is rounded down, it ends up being too small which can cause
> +	 * some monitors to not sync properly. In these instances, adjust htotal
> +	 * and hsync to round the HFP up, and recalculate the htotal. Through trial
> +	 * and error, it appears that the HBP and HSA do not appearto need the same
> +	 * correction that HFP does.
> +	 */
> +	if (dsi->mode_flags & MIPI_DSI_MODE_VIDEO_SYNC_PULSE && dsi->lanes > 1) {

Does this also apply to mode with sync events (I suspect it does), so 
the condition here should likely be if (!...burst mode) , right ?