linux-kernel - Re: [PATCH] drm: clarify adjusted

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Message-ID: <b09d3039-41f7-5de1-7323-2f30ccd7141b@st.com>
Date:   Thu, 19 Apr 2018 15:50:58 +0000
From:   Philippe CORNU <philippe.cornu@...com>
To:     Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Daniel Vetter <daniel.vetter@...el.com>,
        Gustavo Padovan <gustavo@...ovan.org>,
        "Maarten Lankhorst" <maarten.lankhorst@...ux.intel.com>,
        Sean Paul <seanpaul@...omium.org>,
        David Airlie <airlied@...ux.ie>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Archit Taneja <architt@...eaurora.org>
CC:     Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        Yannick FERTRE <yannick.fertre@...com>,
        Vincent ABRIOU <vincent.abriou@...com>
Subject: Re: [PATCH] drm: clarify adjusted_mode documentation for bridges

Hi Archit & Andrzej,

May I ask you please a short review of this documentation update.
Many thanks
Philippe :-)

On 04/09/2018 05:24 PM, Philippe Cornu wrote:
> This patch clarifies the adjusted_mode documentation
> for bridges.
> 
> Signed-off-by: Philippe Cornu <philippe.cornu@...com>
> Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>
> ---
> This patch follows discussions in:
> - "drm: clarify adjusted_mode for a bridge connected to a crtc"
>    https://patchwork.freedesktop.org/patch/206801/
> - "drm: bridge: Constify mode arguments to bridge .mode_set() operation"
>    https://patchwork.freedesktop.org/patch/215449/
> 
>   include/drm/drm_bridge.h | 16 ++++++++++++++++
>   include/drm/drm_crtc.h   | 11 +++++++----
>   2 files changed, 23 insertions(+), 4 deletions(-)
> 
> diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h
> index 3270fec46979..7d632c6a9214 100644
> --- a/include/drm/drm_bridge.h
> +++ b/include/drm/drm_bridge.h
> @@ -178,6 +178,22 @@ struct drm_bridge_funcs {
>   	 * then this would be &drm_encoder_helper_funcs.mode_set. The display
>   	 * pipe (i.e.  clocks and timing signals) is off when this function is
>   	 * called.
> +	 *
> +	 * The adjusted_mode parameter corresponds to the mode output by the CRTC
> +	 * for the first bridge in the chain. It can be different from the mode
> +	 * parameter that contains the desired mode for the connector at the end
> +	 * of the bridges chain, for instance when the first bridge in the chain
> +	 * performs scaling. The adjusted mode is mostly useful for the first
> +	 * bridge in the chain and is likely irrelevant for the other bridges.
> +	 *
> +	 * For atomic drivers the adjusted_mode is the mode stored in
> +	 * &drm_crtc_state.adjusted_mode.
> +	 *
> +	 * NOTE:
> +	 *
> +	 * If a need arises to store and access modes adjusted for other locations
> +	 * than the connection between the CRTC and the first bridge, the DRM
> +	 * framework will have to be extended with DRM bridge states.
>   	 */
>   	void (*mode_set)(struct drm_bridge *bridge,
>   			 struct drm_display_mode *mode,
> diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h
> index a2d81d2907a9..65f749a9e9d3 100644
> --- a/include/drm/drm_crtc.h
> +++ b/include/drm/drm_crtc.h
> @@ -134,10 +134,13 @@ struct drm_crtc_state {
>   	 *
>   	 * Internal display timings which can be used by the driver to handle
>   	 * differences between the mode requested by userspace in @mode and what
> -	 * is actually programmed into the hardware. It is purely driver
> -	 * implementation defined what exactly this adjusted mode means. Usually
> -	 * it is used to store the hardware display timings used between the
> -	 * CRTC and encoder blocks.
> +	 * is actually programmed into the hardware.
> +	 *
> +	 * For drivers using drm_bridge, this stores the hardware display timings
> +	 * used between the CRTC and the first bridge. For other drivers, the
> +	 * meaning of the adjusted_mode field is purely driver implementation
> +	 * defined information, and will usually be used to store the hardware
> +	 * display timings used between the CRTC and encoder blocks.
>   	 */
>   	struct drm_display_mode adjusted_mode;
>   
>