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

From: Laurent Pinchart <laurent.pinchart@ideasonboard•com>
To: Sean Paul <sean@poorly•run>
Cc: Neil Armstrong <narmstrong@baylibre•com>,
	David Airlie <airlied@linux•ie>,
	Linus Walleij <linus.walleij@linaro•org>,
	dri-devel@lists•freedesktop.org,
	Andrzej Hajda <a.hajda@samsung•com>,
	Thierry Reding <thierry.reding@gmail•com>,
	Benjamin Gaignard <benjamin.gaignard@linaro•org>,
	Fabio Estevam <festevam@gmail•com>, Marek Vasut <marex@denx•de>,
	Laurent Pinchart <laurent.pinchart+renesas@ideasonboard•com>,
	Joonyoung Shim <jy0922.shim@samsung•com>,
	Sam Ravnborg <sam@ravnborg•org>,
	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,
	Philipp Zabel <p.zabel@pengutronix•de>,
	NXP Linux Team <linux-imx@nxp•com>,
	Pengutronix Kernel Team <kernel@pengutronix•de>,
	Jonas Karlman <jonas@kwiboo•se>,
	Sascha Hauer <s.hauer@pengutronix•de>,
	Alison Wang <alison.wang@nxp•com>,
	Maarten Lankhorst <maarten.lankhorst@linux•intel.com>,
	Gwan-gyeong Mun <gwan-gyeong.mun@intel•com>,
	Inki Dae <inki.dae@samsung•com>,
	Alexios Zavras <alexios.zavras@intel•com>,
	linux-samsung-soc@vger•kernel.org, Stefan Agner <stefan@agner•ch>,
	linux-tegra@vger•kernel.org, Thomas Gleixner <tglx@linutronix•de>,
	Vincent Abriou <vincent.abriou@st•com>,
	Allison Randal <allison@lohutok•net>,
	Jernej Skrabec <jernej.skrabec@siol•net>,
	Shawn Guo <shawnguo@kernel•org>,
	Seung-Woo Kim <sw0312.kim@samsung•com>,
	Kyungmin Park <kyungmin.park@samsung•com>,
	Daniel Vetter <daniel@ffwll•ch>, Enrico Weigelt <info@metux•net>
Subject: Re: [PATCH v1 14/16] drm/panel: call prepare/enable only once
Date: Mon, 2 Dec 2019 17:15:02 +0200	[thread overview]
Message-ID: <20191202151502.GA18532@pendragon.ideasonboard.com> (raw)
In-Reply-To: <20190805170120.GZ104440@art_vandelay>

Hi Sean,

On Mon, Aug 05, 2019 at 01:01:20PM -0400, Sean Paul wrote:
> 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.

Is this semantics documented somewhere ? The documentation of the panel
disable operation is pretty terse, and we need to explicitly state who
of the caller and callee needs to track the state.

> [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);

-- 
Regards,

Laurent Pinchart

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