[v2,2/2] backlight: lm3630a: add an enable gpio for the HWEN pin

Submitted by Andreas Kemnade on Sept. 10, 2019, 9:29 p.m.

Details

Message ID 20190910212909.18095-3-andreas@kemnade.info
State New
Headers show
Series "backlight_lm3630a: add enable_gpios property" ( rev: 2 ) in DRI devel

Not browsing as part of any series.

Commit Message

Andreas Kemnade Sept. 10, 2019, 9:29 p.m.
For now just enable it in the probe function to allow i2c
access. Disabling also means resetting the register values
to default and according to the datasheet does not give
power savings

Tested on Kobo Clara HD.

Signed-off-by: Andreas Kemnade <andreas@kemnade.info>
---
changes in v2:
- simplification
- correct gpio direction initialisation

 drivers/video/backlight/lm3630a_bl.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

Patch hide | download patch | download mbox

diff --git a/drivers/video/backlight/lm3630a_bl.c b/drivers/video/backlight/lm3630a_bl.c
index 8f84f3684f04..9d0639d4202d 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;
 };
@@ -535,6 +538,13 @@  static int lm3630a_probe(struct i2c_client *client,
 	}
 	pchip->pdata = pdata;
 
+	pchip->enable_gpio = devm_gpiod_get_optional(&client->dev, "enable",
+						GPIOD_OUT_HIGH);
+	if (IS_ERR(pchip->enable_gpio)) {
+		rval = PTR_ERR(pchip->enable_gpio);
+		return rval;
+	}
+
 	/* chip initialize */
 	rval = lm3630a_chip_init(pchip);
 	if (rval < 0) {

Comments

On Tue, Sep 10, 2019 at 11:29:09PM +0200, Andreas Kemnade wrote:
> For now just enable it in the probe function to allow i2c
> access. Disabling also means resetting the register values
> to default and according to the datasheet does not give
> power savings
> 
> Tested on Kobo Clara HD.
> 
> Signed-off-by: Andreas Kemnade <andreas@kemnade.info>
> ---
> changes in v2:
> - simplification
> - correct gpio direction initialisation
> 
>  drivers/video/backlight/lm3630a_bl.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/drivers/video/backlight/lm3630a_bl.c b/drivers/video/backlight/lm3630a_bl.c
> index 8f84f3684f04..9d0639d4202d 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>

Nitpicking... but I don't think linux/gpio.h is used anymore.


>  #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;
>  };
> @@ -535,6 +538,13 @@ static int lm3630a_probe(struct i2c_client *client,
>  	}
>  	pchip->pdata = pdata;
>  
> +	pchip->enable_gpio = devm_gpiod_get_optional(&client->dev, "enable",
> +						GPIOD_OUT_HIGH);
> +	if (IS_ERR(pchip->enable_gpio)) {
> +		rval = PTR_ERR(pchip->enable_gpio);
> +		return rval;
> +	}
> +
>  	/* chip initialize */
>  	rval = lm3630a_chip_init(pchip);
>  	if (rval < 0) {
> -- 
> 2.20.1
>
On 9/11/19 5:25 AM, Daniel Thompson wrote:
> On Tue, Sep 10, 2019 at 11:29:09PM +0200, Andreas Kemnade wrote:
>> For now just enable it in the probe function to allow i2c
>> access. Disabling also means resetting the register values
>> to default and according to the datasheet does not give
>> power savings
>>
>> Tested on Kobo Clara HD.
>>
>> Signed-off-by: Andreas Kemnade <andreas@kemnade.info>
>> ---
>> changes in v2:
>> - simplification
>> - correct gpio direction initialisation
>>
>>   drivers/video/backlight/lm3630a_bl.c | 10 ++++++++++
>>   1 file changed, 10 insertions(+)
>>
>> diff --git a/drivers/video/backlight/lm3630a_bl.c b/drivers/video/backlight/lm3630a_bl.c
>> index 8f84f3684f04..9d0639d4202d 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>
> Nitpicking... but I don't think linux/gpio.h is used anymore.
>
>
>>   #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;
>>   };
>> @@ -535,6 +538,13 @@ static int lm3630a_probe(struct i2c_client *client,
>>   	}
>>   	pchip->pdata = pdata;
>>   
>> +	pchip->enable_gpio = devm_gpiod_get_optional(&client->dev, "enable",
>> +						GPIOD_OUT_HIGH);
>> +	if (IS_ERR(pchip->enable_gpio)) {
>> +		rval = PTR_ERR(pchip->enable_gpio);
>> +		return rval;

the enable gpio is optional so if it fails you log the error and move on

Also on driver removal did you want to set the GPIO to low to disable 
the device to save power?

Dan


>> +	}
>> +
>>   	/* chip initialize */
>>   	rval = lm3630a_chip_init(pchip);
>>   	if (rval < 0) {
>> -- 
>> 2.20.1
>>
On Wed, 11 Sep 2019 13:48:36 -0500
Dan Murphy <dmurphy@ti.com> wrote:


> >> @@ -535,6 +538,13 @@ static int lm3630a_probe(struct i2c_client *client,
> >>   	}
> >>   	pchip->pdata = pdata;
> >>   
> >> +	pchip->enable_gpio = devm_gpiod_get_optional(&client->dev, "enable",
> >> +						GPIOD_OUT_HIGH);
> >> +	if (IS_ERR(pchip->enable_gpio)) {
> >> +		rval = PTR_ERR(pchip->enable_gpio);
> >> +		return rval;  
> 
> the enable gpio is optional so if it fails you log the error and move on
>
well, if the gpio is not there, then it returns NULL.
It might return e.g. -EDEFER. So I need to check for errors here.
 
> Also on driver removal did you want to set the GPIO to low to disable 
> the device to save power?
> 
page 5 of the datasheet says:

Ishdn = Typ. 1µA max. 4µA.
For HWEN=Vin, I2c shutdown  (I guess this means outputs powered off)
ond for HWEN=GND.

So are we really saving something here?

Regards,
Andreas
On Wed, Sep 11, 2019 at 01:48:36PM -0500, Dan Murphy wrote:
> 
> On 9/11/19 5:25 AM, Daniel Thompson wrote:
> > On Tue, Sep 10, 2019 at 11:29:09PM +0200, Andreas Kemnade wrote:
> > > For now just enable it in the probe function to allow i2c
> > > access. Disabling also means resetting the register values
> > > to default and according to the datasheet does not give
> > > power savings
> > > 
> > > Tested on Kobo Clara HD.
> > > 
> > > Signed-off-by: Andreas Kemnade <andreas@kemnade.info>
> > > ---
> > > changes in v2:
> > > - simplification
> > > - correct gpio direction initialisation
> > > 
> > >   drivers/video/backlight/lm3630a_bl.c | 10 ++++++++++
> > >   1 file changed, 10 insertions(+)
> > > 
> > > diff --git a/drivers/video/backlight/lm3630a_bl.c b/drivers/video/backlight/lm3630a_bl.c
> > > index 8f84f3684f04..9d0639d4202d 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>
> > Nitpicking... but I don't think linux/gpio.h is used anymore.
> > 
> > 
> > >   #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;
> > >   };
> > > @@ -535,6 +538,13 @@ static int lm3630a_probe(struct i2c_client *client,
> > >   	}
> > >   	pchip->pdata = pdata;
> > > +	pchip->enable_gpio = devm_gpiod_get_optional(&client->dev, "enable",
> > > +						GPIOD_OUT_HIGH);
> > > +	if (IS_ERR(pchip->enable_gpio)) {
> > > +		rval = PTR_ERR(pchip->enable_gpio);
> > > +		return rval;
> 
> the enable gpio is optional so if it fails you log the error and move on

Isn't the effect of this to cope gracefully if enable-gpios is absent
but to fail with an error if enable-gpios exists and is broken. I
thought this code pattern is fairly common.


> Also on driver removal did you want to set the GPIO to low to disable the
> device to save power?

As it happens I offered to opposite feedback for v1:
https://lists.freedesktop.org/archives/dri-devel/2019-September/234918.html

Basically if the power matters then we should take care of things in the
PM code path (which for this driver means reacting properly to
suspended flag when updating the brightness). If the power doesn't matter
then, given unallocated GPIO pins are in an unknown state anyway, there
is no point in tidying up because we don't know what value to restore.


Daniel.