Re: [PATCH v1 14/16] drm/panel: call prepare/enable only once

From: Sean Paul <sean@poorly.run>
To: Sam Ravnborg <sam@ravnborg.org>
Cc: Neil Armstrong <narmstrong@baylibre.com>,
	David Airlie <airlied@linux.ie>,
	dri-devel@lists.freedesktop.org,
	Thierry Reding <thierry.reding@gmail.com>,
	Laurent Pinchart <Laurent.pinchart@ideasonboard.com>,
	Marek Vasut <marex@denx.de>,
	Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>,
	Vincent Abriou <vincent.abriou@st.com>,
	Krzysztof Kozlowski <krzk@kernel.org>,
	Jonathan Hunter <jonathanh@nvidia.com>,
	Maxime Ripard <maxime.ripard@bootlin.com>,
	Kukjin Kim <kgene@kernel.org>,
	linux-arm-kernel@lists.infradead.org,
	NXP Linux Team <linux-imx@nxp.com>,
	Pengutronix Kernel Team <kernel@pengutronix.de>,
	Jonas Karlman <jonas@kwiboo.se>,
	Alison Wang <alison.wang@nxp.com>,
	Gwan-gyeong Mun <gwan-gyeong.mun@intel.com>,
	Alexios Zavras <alexios.zavras@intel.com>,
	linux-samsung-soc@vger.kernel.org, linux-tegra@vger.kernel.org,
	Thomas Gleixner <tglx@linutronix.de>Sean Paul <s>
Subject: Re: [PATCH v1 14/16] drm/panel: call prepare/enable only once
Date: Mon, 5 Aug 2019 13:01:20 -0400	[thread overview]
Message-ID: <20190805170120.GZ104440@art_vandelay> (raw)
In-Reply-To: <20190804201637.1240-15-sam@ravnborg.org>

On Sun, Aug 04, 2019 at 10:16:35PM +0200, Sam Ravnborg wrote:
> Many panel drivers duplicate logic to prevent prepare to be called
> for a panel that is already prepared.
> Likewise for enable.
> 
> Implement this logic in drm_panel so the individual drivers
> no longer needs this.
> A panel is considered prepared/enabled only if the prepare/enable call
> succeeds.
> For disable/unprepare it is unconditionally considered
> disabled/unprepared.

Hi Sam,
I did a similar thing a few years ago [1]. IIRC it was well received and just
needed some nits cleaned up. Unfortunately I lost interest^W^W switched to other
things and dropped it. So thanks for picking this back up!

Fast forward to today, I still think it's a good idea but I want to make sure
this won't negatively interact with the self refresh helpers. With the helpers
in place, it's possible to call disable consecutively (ie: once to enter self
refresh and again to actually shut down). I did a quick pass and it looks like
this patch might break that behavior, so you might want to take that into
account.

Sean

[1]- https://patchwork.freedesktop.org/series/30712/

> 
> This allows calls to prepare/enable again, even if there were
> some issue disabling a regulator or similar during disable/unprepare.
> 
> Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> Cc: Maxime Ripard <maxime.ripard@bootlin.com>
> Cc: Sean Paul <sean@poorly.run>
> Cc: Thierry Reding <thierry.reding@gmail.com>
> Cc: Sam Ravnborg <sam@ravnborg.org>
> Cc: David Airlie <airlied@linux.ie>
> Cc: Daniel Vetter <daniel@ffwll.ch>
> ---
>  drivers/gpu/drm/drm_panel.c | 66 ++++++++++++++++++++++++++++++-------
>  include/drm/drm_panel.h     | 21 ++++++++++++
>  2 files changed, 75 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_panel.c b/drivers/gpu/drm/drm_panel.c
> index da19d5b4a2f4..0853764040de 100644
> --- a/drivers/gpu/drm/drm_panel.c
> +++ b/drivers/gpu/drm/drm_panel.c
> @@ -66,10 +66,21 @@ EXPORT_SYMBOL(drm_panel_init);
>   */
>  int drm_panel_prepare(struct drm_panel *panel)
>  {
> -	if (panel && panel->funcs && panel->funcs->prepare)
> -		return panel->funcs->prepare(panel);
> +	int ret = -ENOSYS;
>  
> -	return panel ? -ENOSYS : -EINVAL;
> +	if (!panel)
> +		return -EINVAL;
> +
> +	if (panel->prepared)
> +		return 0;
> +
> +	if (panel->funcs && panel->funcs->prepare)
> +		ret = panel->funcs->prepare(panel);
> +
> +	if (ret >= 0)
> +		panel->prepared = true;
> +
> +	return ret;
>  }
>  EXPORT_SYMBOL(drm_panel_prepare);
>  
> @@ -85,10 +96,21 @@ EXPORT_SYMBOL(drm_panel_prepare);
>   */
>  int drm_panel_enable(struct drm_panel *panel)
>  {
> -	if (panel && panel->funcs && panel->funcs->enable)
> -		return panel->funcs->enable(panel);
> +	int ret = -ENOSYS;
>  
> -	return panel ? -ENOSYS : -EINVAL;
> +	if (!panel)
> +		return -EINVAL;
> +
> +	if (panel->enabled)
> +		return 0;
> +
> +	if (panel->funcs && panel->funcs->enable)
> +		ret = panel->funcs->enable(panel);
> +
> +	if (ret >= 0)
> +		panel->enabled = true;
> +
> +	return ret;
>  }
>  EXPORT_SYMBOL(drm_panel_enable);
>  
> @@ -104,10 +126,20 @@ EXPORT_SYMBOL(drm_panel_enable);
>   */
>  int drm_panel_disable(struct drm_panel *panel)
>  {
> -	if (panel && panel->funcs && panel->funcs->disable)
> -		return panel->funcs->disable(panel);
> +	int ret = -ENOSYS;
>  
> -	return panel ? -ENOSYS : -EINVAL;
> +	if (!panel)
> +		return -EINVAL;
> +
> +	if (!panel->enabled)
> +		return 0;
> +
> +	if (panel->funcs && panel->funcs->disable)
> +		ret = panel->funcs->disable(panel);
> +
> +	panel->enabled = false;
> +
> +	return ret;
>  }
>  EXPORT_SYMBOL(drm_panel_disable);
>  
> @@ -124,10 +156,20 @@ EXPORT_SYMBOL(drm_panel_disable);
>   */
>  int drm_panel_unprepare(struct drm_panel *panel)
>  {
> -	if (panel && panel->funcs && panel->funcs->unprepare)
> -		return panel->funcs->unprepare(panel);
> +	int ret = -ENOSYS;
>  
> -	return panel ? -ENOSYS : -EINVAL;
> +	if (!panel)
> +		return -EINVAL;
> +
> +	if (!panel->prepared)
> +		return 0;
> +
> +	if (panel->funcs && panel->funcs->unprepare)
> +		ret = panel->funcs->unprepare(panel);
> +
> +	panel->prepared = false;
> +
> +	return ret;
>  }
>  EXPORT_SYMBOL(drm_panel_unprepare);
>  
> diff --git a/include/drm/drm_panel.h b/include/drm/drm_panel.h
> index 624bd15ecfab..7493500fc9bd 100644
> --- a/include/drm/drm_panel.h
> +++ b/include/drm/drm_panel.h
> @@ -65,6 +65,9 @@ struct drm_panel_funcs {
>  	 * @prepare:
>  	 *
>  	 * Turn on panel and perform set up.
> +	 * When the panel is successfully prepared the prepare() function
> +	 * will not be called again until the panel has been unprepared.
> +	 *
>  	 */
>  	int (*prepare)(struct drm_panel *panel);
>  
> @@ -72,6 +75,8 @@ struct drm_panel_funcs {
>  	 * @enable:
>  	 *
>  	 * Enable panel (turn on back light, etc.).
> +	 * When the panel is successfully enabled the enable() function
> +	 * will not be called again until the panel has been disabled.
>  	 */
>  	int (*enable)(struct drm_panel *panel);
>  
> @@ -79,6 +84,7 @@ struct drm_panel_funcs {
>  	 * @disable:
>  	 *
>  	 * Disable panel (turn off back light, etc.).
> +	 * If the panel is already disabled the disable() function is not called.
>  	 */
>  	int (*disable)(struct drm_panel *panel);
>  
> @@ -86,6 +92,7 @@ struct drm_panel_funcs {
>  	 * @unprepare:
>  	 *
>  	 * Turn off panel.
> +	 * If the panel is already unprepared the unprepare() function is not called.
>  	 */
>  	int (*unprepare)(struct drm_panel *panel);
>  
> @@ -145,6 +152,20 @@ struct drm_panel {
>  	 * Panel entry in registry.
>  	 */
>  	struct list_head list;
> +
> +	/**
> +	 * @prepared:
> +	 *
> +	 * Set to true when the panel is successfully prepared.
> +	 */
> +	bool prepared;
> +
> +	/**
> +	 * @enabled:
> +	 *
> +	 * Set to true when the panel is successfully enabled.
> +	 */
> +	bool enabled;
>  };
>  
>  void drm_panel_init(struct drm_panel *panel);
> -- 
> 2.20.1
> 

-- 
Sean Paul, Software Engineer, Google / Chromium OS
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