linux-kernel - Re: [PATCH v2 2/3] backlight: tdo24m: add the reset line gpio

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Date:   Sun, 17 Dec 2017 20:57:20 +0000
From:   Daniel Thompson <daniel.thompson@...aro.org>
To:     Robert Jarzmik <robert.jarzmik@...e.fr>
Cc:     Lee Jones <lee.jones@...aro.org>,
        Jingoo Han <jingoohan1@...il.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        linux-fbdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/3] backlight: tdo24m: add the reset line gpio

On Sat, Dec 16, 2017 at 12:39:50PM +0100, Robert Jarzmik wrote:
> Daniel Thompson <daniel.thompson@...aro.org> writes:
> > On Fri, Oct 13, 2017 at 09:42:48PM +0200, Robert Jarzmik wrote:
> >> The Toppoly panels have a global reset line. Add an optional gpio
> >> control for this line, for platforms which have the ability to drive it.
> >> 
> >> Signed-off-by: Robert Jarzmik <robert.jarzmik@...e.fr>
> >> ---
> >>  drivers/video/backlight/tdo24m.c | 3 +++
> >>  1 file changed, 3 insertions(+)
> >> 
> >> diff --git a/drivers/video/backlight/tdo24m.c b/drivers/video/backlight/tdo24m.c
> >> index e4bd63e9db6b..e4b2dfabf192 100644
> >> --- a/drivers/video/backlight/tdo24m.c
> >> +++ b/drivers/video/backlight/tdo24m.c
> >> @@ -10,6 +10,7 @@
> >>   */
> >>  
> >>  #include <linux/module.h>
> >> +#include <linux/gpio/consumer.h>
> >>  #include <linux/kernel.h>
> >>  #include <linux/init.h>
> >>  #include <linux/device.h>
> >> @@ -32,6 +33,7 @@ struct tdo24m {
> >>  	struct spi_message	msg;
> >>  	struct spi_transfer	xfer;
> >>  	uint8_t			*buf;
> >> +	struct gpio_desc	*xres;
> >
> > Why do we need a write-only variable?
> It's written to by devm_gpiod_get() below.

Yes, but it not *read* anywhere because we rely on devm to release the GPIO.
Why do we need a write-only variable?


> >> +	lcd->xres = devm_gpiod_get(&spi->dev, "reset", GPIOD_OUT_LOW);
> >
> > devm_gpiod_get_optional() would be better, if only for its commenting
> > value.
> Yes, you're perfectly right.
> 
> > Also, this adds a new optional property, doesn't the devicetree binding 
> > docs need to be update to match this?
> Ah yes, that too. I'll add it for v3.

Thanks!


Daniel.