linux-kernel - Re: [PATCH 3/5] drm/panel: Add attach/detach callbacks

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Date:   Tue, 11 Jun 2019 10:57:22 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Derek Basehore <dbasehore@...omium.org>
Cc:     linux-kernel@...r.kernel.org,
        Thierry Reding <thierry.reding@...il.com>,
        Sam Ravnborg <sam@...nborg.org>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Sean Paul <sean@...rly.run>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        CK Hu <ck.hu@...iatek.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Matthias Brugger <matthias.bgg@...il.com>,
        dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
        intel-gfx@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH 3/5] drm/panel: Add attach/detach callbacks

On Mon, Jun 10, 2019 at 09:03:48PM -0700, Derek Basehore wrote:
> This adds the attach/detach callbacks. These are for setting up
> internal state for the connector/panel pair that can't be done at
> probe (since the connector doesn't exist) and which don't need to be
> repeatedly done for every get/modes, prepare, or enable callback.
> Values such as the panel orientation, and display size can be filled
> in for the connector.
> 
> Signed-off-by: Derek Basehore <dbasehore@...omium.org>
> ---
>  drivers/gpu/drm/drm_panel.c | 14 ++++++++++++++
>  include/drm/drm_panel.h     |  4 ++++
>  2 files changed, 18 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_panel.c b/drivers/gpu/drm/drm_panel.c
> index 3b689ce4a51a..72f67678d9d5 100644
> --- a/drivers/gpu/drm/drm_panel.c
> +++ b/drivers/gpu/drm/drm_panel.c
> @@ -104,12 +104,23 @@ EXPORT_SYMBOL(drm_panel_remove);
>   */
>  int drm_panel_attach(struct drm_panel *panel, struct drm_connector *connector)
>  {
> +	int ret;
> +
>  	if (panel->connector)
>  		return -EBUSY;
>  
>  	panel->connector = connector;
>  	panel->drm = connector->dev;
>  
> +	if (panel->funcs->attach) {
> +		ret = panel->funcs->attach(panel);
> +		if (ret < 0) {
> +			panel->connector = NULL;
> +			panel->drm = NULL;
> +			return ret;
> +		}
> +	}

Why can't we just implement this in the drm helpers for everyone, by e.g.
storing a dt node in drm_panel? Feels a bit overkill to have these new
hooks here.

Also, my understanding is that this dt stuff is supposed to be
standardized, so this should work.
-Daniel

> +
>  	return 0;
>  }
>  EXPORT_SYMBOL(drm_panel_attach);
> @@ -128,6 +139,9 @@ EXPORT_SYMBOL(drm_panel_attach);
>   */
>  int drm_panel_detach(struct drm_panel *panel)
>  {
> +	if (panel->funcs->detach)
> +		panel->funcs->detach(panel);
> +
>  	panel->connector = NULL;
>  	panel->drm = NULL;
>  
> diff --git a/include/drm/drm_panel.h b/include/drm/drm_panel.h
> index 13631b2efbaa..e136e3a3c996 100644
> --- a/include/drm/drm_panel.h
> +++ b/include/drm/drm_panel.h
> @@ -37,6 +37,8 @@ struct display_timing;
>   * struct drm_panel_funcs - perform operations on a given panel
>   * @disable: disable panel (turn off back light, etc.)
>   * @unprepare: turn off panel
> + * @detach: detach panel->connector (clear internal state, etc.)
> + * @attach: attach panel->connector (update internal state, etc.)
>   * @prepare: turn on panel and perform set up
>   * @enable: enable panel (turn on back light, etc.)
>   * @get_modes: add modes to the connector that the panel is attached to and
> @@ -70,6 +72,8 @@ struct display_timing;
>  struct drm_panel_funcs {
>  	int (*disable)(struct drm_panel *panel);
>  	int (*unprepare)(struct drm_panel *panel);
> +	void (*detach)(struct drm_panel *panel);
> +	int (*attach)(struct drm_panel *panel);
>  	int (*prepare)(struct drm_panel *panel);
>  	int (*enable)(struct drm_panel *panel);
>  	int (*get_modes)(struct drm_panel *panel);
> -- 
> 2.22.0.rc2.383.gf4fbbf30c2-goog
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch