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Re: [PATCH v2] pwm-backlight: fix the panel power sequence

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  Re: [PATCH v2] pwm-backlight: fix the panel power sequence YH Huang <yh.huang@mediatek.com> - 2015-11-03 09:20 +0100
    Re: [PATCH v2] pwm-backlight: fix the panel power sequence Philipp Zabel <p.zabel@pengutronix.de> - 2015-11-03 12:10 +0100
      Re: [PATCH v2] pwm-backlight: fix the panel power sequence YH Huang <yh.huang@mediatek.com> - 2015-11-04 02:50 +0100
        Re: [PATCH v2] pwm-backlight: fix the panel power sequence Philipp Zabel <p.zabel@pengutronix.de> - 2015-11-05 10:50 +0100
          Re: [PATCH v2] pwm-backlight: fix the panel power sequence YH Huang <yh.huang@mediatek.com> - 2015-11-06 09:40 +0100

#1261281 — Re: [PATCH v2] pwm-backlight: fix the panel power sequence

On Fri, 2015-10-30 at 11:34 +0100, Philipp Zabel wrote:
> Am Freitag, den 30.10.2015, 15:41 +0800 schrieb YH Huang:
> > > That won't work if the gpio is still configured as input. How about I
> > > add the GPIOD_ASIS change to my patch you remove that and the above from
> > > yours?
> > 
> > I revise these two lines 
> > if (pb->enable_gpio)
> > 	gpiod_direction_output(pb->enable_gpio, 0);
> > into
> > if (pb->enable_gpio) {
> > 	if(gpiod_get_value(pb->enable_gpio) == 0)
> > 		gpiod_direction_output(pb->enable_gpio, 0);
> > 	else
> > 		gpiod_direction_output(pb->enable_gpio, 1);
> > }
> 
> If the GPIO is still configured as an input, the return value of
> gpiod_get_value could be random.
> 
> > I am not sure what "phandle" is working for.
> 
> 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?

Before this patch ( http://patchwork.ozlabs.org/patch/324690/ ),
we disable "enable-gpio" in the probe function.

Do you have any idea of this?

Regards,
YH Huang


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#1261390

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.

regards
Philipp

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#1262023

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);
	else
		gpiod_direction_output(pb->enable_gpio, 0);
}

And then update with props.brightness in backlight_update_status.
I am not sure, maybe I miss something.

Regards,
YH Huang

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#1263052

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

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#1263837

On Thu, 2015-11-05 at 10:40 +0100, Philipp Zabel wrote:
> > 
> > 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.

Thanks your kindly reply.
Your patch looks good to me.

Regards,
YH Huang

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