Am Mittwoch, den 04.11.2015, 09:47 +0800 schrieb YH Huang:

On Tue, 2015-11-03 at 12:08 +0100, Philipp Zabel wrote:

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Hi YH,

Am Dienstag, den 03.11.2015, 16:11 +0800 schrieb YH Huang:

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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.

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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