linux-kernel - Re: [PATCH 1/3] drm/bridge: samsung-dsim: move bridge init sequence to atomic

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Message-ID: <1db5ffdf-924b-49cb-a057-802a1bfe6073@samsung.com>
Date: Mon, 26 Jan 2026 09:57:01 +0100
From: Marek Szyprowski <m.szyprowski@...sung.com>
To: Kaustabh Chakraborty <kauschluss@...root.org>, Inki Dae
	<inki.dae@...sung.com>, Jagan Teki <jagan@...rulasolutions.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>,
	Simona Vetter <simona@...ll.ch>
Cc: dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Subject: Re: [PATCH 1/3] drm/bridge: samsung-dsim: move bridge init sequence
 to atomic_enable

On 24.01.2026 18:20, Kaustabh Chakraborty wrote:
> Since commit c9b1150a68d9 ("drm/atomic-helper: Re-order bridge chain
> pre-enable and post-disable"), pre-enable sequence is called before the
> CRTC is enabled.
>
> This causes unintended side-effects (abberation among potentially other
> things) in the display when samsung_dsim_init() is called in the
> pre-enable part of the sequence. Call it in samsung_dsim_atomic_enable()
> instead.
>
> Cc: stable@...r.kernel.org # v6.17 and later
> Signed-off-by: Kaustabh Chakraborty <kauschluss@...root.org>

I'm not sure if this will be needed:

https://lore.kernel.org/all/20251205-drm-seq-fix-v1-0-fda68fa1b3de@ideasonboard.com/


> ---
>   drivers/gpu/drm/bridge/samsung-dsim.c | 13 +++++++------
>   1 file changed, 7 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/bridge/samsung-dsim.c b/drivers/gpu/drm/bridge/samsung-dsim.c
> index 1d85e706c74b9..975f8b50ae660 100644
> --- a/drivers/gpu/drm/bridge/samsung-dsim.c
> +++ b/drivers/gpu/drm/bridge/samsung-dsim.c
> @@ -1655,6 +1655,13 @@ static void samsung_dsim_atomic_pre_enable(struct drm_bridge *bridge,
>   	}
>   
>   	dsi->state |= DSIM_STATE_ENABLED;
> +}
> +
> +static void samsung_dsim_atomic_enable(struct drm_bridge *bridge,
> +				       struct drm_atomic_state *state)
> +{
> +	struct samsung_dsim *dsi = bridge_to_dsi(bridge);
> +	int ret;
>   
>   	/*
>   	 * For Exynos-DSIM the downstream bridge, or panel are expecting
> @@ -1665,12 +1672,6 @@ static void samsung_dsim_atomic_pre_enable(struct drm_bridge *bridge,
>   		if (ret)
>   			return;
>   	}
> -}
> -
> -static void samsung_dsim_atomic_enable(struct drm_bridge *bridge,
> -				       struct drm_atomic_state *state)
> -{
> -	struct samsung_dsim *dsi = bridge_to_dsi(bridge);
>   
>   	samsung_dsim_set_display_mode(dsi);
>   	samsung_dsim_set_display_enable(dsi, true);
>
Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland