From mboxrd@z Thu Jan 1 00:00:00 1970
From: Philipp Zabel
Date: Thu, 05 Nov 2015 09:40:30 +0000
Subject: Re: [PATCH v2] pwm-backlight: fix the panel power sequence
Message-Id: <1446716430.3894.12.camel@pengutronix.de>
List-Id:
References: <1444987060-48202-1-git-send-email-yh.huang@mediatek.com>
<1444988219.3541.3.camel@pengutronix.de>
<1445526750.27586.8.camel@mtksdaap41>
<1446133259.3274.52.camel@pengutronix.de>
<1446190900.17558.16.camel@mtksdaap41>
<1446201271.3334.22.camel@pengutronix.de>
<1446538299.2449.8.camel@mtksdaap41>
<1446548924.3373.3.camel@pengutronix.de>
<1446601656.15340.11.camel@mtksdaap41>
In-Reply-To: <1446601656.15340.11.camel@mtksdaap41>
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
To: linux-arm-kernel@lists.infradead.org
Am Mittwoch, den 04.11.2015, 09:47 +0800 schrieb YH Huang:
> On Tue, 2015-11-03 at 12:08 +0100, Philipp Zabel wrote:
> > Hi YH,
> >
> > Am Dienstag, den 03.11.2015, 16:11 +0800 schrieb YH Huang:
> > > > The reasoning is that devices where there is no phandle link pointing to
> > > > the backlight (for example from a simple-panel node), we should keep the
> > > > current default behaviour (enable during probe).
> > >
> > > I have a little problem for the current default behaviour.
> > > Should we enable during probe?
> >
> > Here I mean enabling the backlight (at the end of the probe function),
> > not enabling the GPIO already when requesting it.
> >
> > > Before this patch ( http://patchwork.ozlabs.org/patch/324690/ ),
> > > we disable "enable-gpio" in the probe function.
> >
> > While before this patch the GPIO would be initialized in the disabled
> > state, the call to backlight_update_status at the end of the probe
> > function would still enable the backlight afterwards.
>
> Based on this, could we disable it initially and update in the
> backlight_update_status function?
>
> Like this,
>
> if (pb->enable_gpio) {
> if (phandle &&
> gpiod_get_direction(pb->enable_gpio) = GPIOF_DIR_OUT &&
> gpiod_get_value(pb->enable_gpio) = 1)
> gpiod_direction_output(pb->enable_gpio, 1);
The gpiod_direction_output call is a no-op, since the direction is
already output and the value is already 1.
Also, I propose to set initial blanking to FB_BLANK_POWERDOWN in this
case, and wait for the panel driver to enable the backlight at the
appropriate time.
regards
Philipp