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SubjectRe: [PATCH 1/2] backlight: lm3630a: add an enable gpio for the HWEN pin
On Mon, 9 Sep 2019 11:57:29 +0100
Daniel Thompson <daniel.thompson@linaro.org> wrote:

> On Sun, Sep 08, 2019 at 10:37:03PM +0200, Andreas Kemnade wrote:
> > For now just enable it in the probe function to allow i2c
> > access and disable it on remove. Disabling also means resetting
> > the register values to default.
> >
> > Tested on Kobo Clara HD.
> >
> > Signed-off-by: Andreas Kemnade <andreas@kemnade.info>
> > ---
> > drivers/video/backlight/lm3630a_bl.c | 18 ++++++++++++++++++
> > 1 file changed, 18 insertions(+)
> >
> > diff --git a/drivers/video/backlight/lm3630a_bl.c b/drivers/video/backlight/lm3630a_bl.c
> > index b04b35d007a2..3b45a1733198 100644
> > --- a/drivers/video/backlight/lm3630a_bl.c
> > +++ b/drivers/video/backlight/lm3630a_bl.c
> > @@ -12,6 +12,8 @@
> > #include <linux/uaccess.h>
> > #include <linux/interrupt.h>
> > #include <linux/regmap.h>
> > +#include <linux/gpio/consumer.h>
> > +#include <linux/gpio.h>
> > #include <linux/pwm.h>
> > #include <linux/platform_data/lm3630a_bl.h>
> >
> > @@ -48,6 +50,7 @@ struct lm3630a_chip {
> > struct lm3630a_platform_data *pdata;
> > struct backlight_device *bleda;
> > struct backlight_device *bledb;
> > + struct gpio_desc *enable_gpio;
> > struct regmap *regmap;
> > struct pwm_device *pwmd;
> > };
> > @@ -506,6 +509,14 @@ static int lm3630a_probe(struct i2c_client *client,
> > return -ENOMEM;
> > pchip->dev = &client->dev;
> >
> > + pchip->enable_gpio = devm_gpiod_get_optional(&client->dev, "enable",
> > + GPIOD_ASIS);
>
> Initializing GPIOD_ASIS doesn't look right to me.
>
> If you initialize ASIS then the driver must configure the pin as an
> output... far easier just to set GPIOD_OUT_HIGH during the get.
>
> Note also that the call to this function should also be moved *below*
> the calls parse the DT.
>
oops, must have forgotten that, and had good luck here.
>
> > + if (IS_ERR(pchip->enable_gpio)) {
> > + rval = PTR_ERR(pchip->enable_gpio);
> > + return rval;
> > + }
> > +
> > +
> > pchip->regmap = devm_regmap_init_i2c(client, &lm3630a_regmap);
> > if (IS_ERR(pchip->regmap)) {
> > rval = PTR_ERR(pchip->regmap);
> > @@ -535,6 +546,10 @@ static int lm3630a_probe(struct i2c_client *client,
> > }
> > pchip->pdata = pdata;
> >
> > + if (pchip->enable_gpio) {
> > + gpiod_set_value_cansleep(pchip->enable_gpio, 1);
>
> Not needed, use GPIOD_OUT_HIGH instead.
>
>
> > + usleep_range(1000, 2000);
>
> Not needed, this sleep is already part of lm3630a_chip_init().
>
you are right.
>
> > + }
> > /* chip initialize */
> > rval = lm3630a_chip_init(pchip);
> > if (rval < 0) {
> > @@ -586,6 +601,9 @@ static int lm3630a_remove(struct i2c_client *client)
> > if (rval < 0)
> > dev_err(pchip->dev, "i2c failed to access register\n");
> >
> > + if (pchip->enable_gpio)
> > + gpiod_set_value_cansleep(pchip->enable_gpio, 0);
> > +
>
> Is this needed?
>
> This is a remove path, not a power management path, and we have no idea
> what the original status of the pin was anyway?
>

Looking at Ishdn on page 5 of the datasheet, switching it off everytime
possible seems not needed. We would need to call chip_init() everytime
we enable the gpio or live with default values.
Therefore I did decide to not put it into any power management path. But
switching it on and not switching it off feels so unbalanced.

Regards,
Andreas

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