From mboxrd@z Thu Jan  1 00:00:00 1970
From: Emil Velikov <emil.l.velikov@gmail.com>
Subject: Re: [PATCH v1 14/16] drm/panel: call prepare/enable only once
Date: Mon, 5 Aug 2019 14:15:55 +0100
Message-ID: <20190805131555.GA5005@arch-x1c3>
References: <20190804201637.1240-1-sam@ravnborg.org>
 <20190804201637.1240-15-sam@ravnborg.org>
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To: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Neil Armstrong <narmstrong@baylibre.com>, David Airlie <airlied@linux.ie>, dri-devel@lists.freedesktop.org, Thierry Reding <thierry.reding@gmail.com>, Sam Ravnborg <sam@ravnborg.org>, Marek Vasut <marex@denx.de>, linux-samsung-soc@vger.kernel.org, Sean Paul <sean@poorly.run>, Allison Randal <allison@lohutok.net>, Krzysztof Kozlowski <krzk@kernel.org>, Jonathan Hunter <jonathanh@nvidia.com>, Maxime Ripard <maxime.ripard@bootlin.com>, Kukjin Kim <kgene@kernel.org>, NXP Linux Team <linux-imx@nxp.com>, 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>, Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>, linux-tegra@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>, Vincent Abriou <vincent.abriou@st.com>, linux-arm-kernel@lists.infradead.org
List-Id: linux-tegra@vger.kernel.org

On 2019/08/05, Laurent Pinchart wrote:
> Hi Sam,
> 
> Thank you for the patch.
> 
> 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.
> > 
> > This allows calls to prepare/enable again, even if there were
> > some issue disabling a regulator or similar during disable/unprepare.
> 
> Is this the right place to handle this ? Shouldn't the upper layers
> ensure than enable/disable and prepare/unprepare are correcty balanced,
> and not called multiple times ? Adding enabled and prepared state to
> drm_panel not only doesn't align well with atomic state handling, but
> also would hide issues in upper layers that should really be fixed
> there.
> 
Fully agreed. Mistakes happen - hiding them, by returning "success" does
not sound like a wise approach.

HTH
Emil