linux-kernel - Re: [PATCH 2/2] hwmon: (sy7636a) enable regulator only if needed

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250924224035.2b20459a@kemnade.info>
Date: Wed, 24 Sep 2025 22:40:35 +0200
From: Andreas Kemnade <andreas@...nade.info>
To: Guenter Roeck <linux@...ck-us.net>
Cc: jdelvare@...e.com, lgirdwood@...il.com, broonie@...nel.org,
 linux-hwmon@...r.kernel.org, linux-kernel@...r.kernel.org, Alistair Francis
 <alistair@...stair23.me>
Subject: Re: [PATCH 2/2] hwmon: (sy7636a) enable regulator only if needed

On Wed, 24 Sep 2025 09:06:15 -0700
Guenter Roeck <linux@...ck-us.net> wrote:

> On Sat, Sep 20, 2025 at 01:43:11PM +0200, Andreas Kemnade wrote:
> > Avoid having all the regulators in the SY7636A enabled all the time
> > to significantly reduce current consumption. In pratical scenarios,
> > the regulators are only needed when a refresh is done on the epaper
> > display powered by the SY7636A. This is can save around 10mA which
> > is much for this kind of devices.
> > Also fixes the asymmetrical single enable call.
> > 
> > Signed-off-by: Andreas Kemnade <andreas@...nade.info>
> > ---
> >  drivers/hwmon/sy7636a-hwmon.c | 34 ++++++++++++++++++++++++----------
> >  1 file changed, 24 insertions(+), 10 deletions(-)
> > 
> > diff --git a/drivers/hwmon/sy7636a-hwmon.c b/drivers/hwmon/sy7636a-hwmon.c
> > index e83d0e50c735..0fda69bea3b4 100644
> > --- a/drivers/hwmon/sy7636a-hwmon.c
> > +++ b/drivers/hwmon/sy7636a-hwmon.c
> > @@ -18,14 +18,26 @@
> >  
> >  #include <linux/mfd/sy7636a.h>
> >  
> > +struct sy7636a_hwmon_data {
> > +	struct regmap *regmap;
> > +	struct regulator *regulator;
> > +};
> > +
> > +
> >  static int sy7636a_read(struct device *dev, enum hwmon_sensor_types type,
> >  			u32 attr, int channel, long *temp)
> >  {
> > -	struct regmap *regmap = dev_get_drvdata(dev);
> > +	struct sy7636a_hwmon_data *drvdata = dev_get_drvdata(dev);
> >  	int ret, reg_val;
> >  
> > -	ret = regmap_read(regmap,
> > +	ret = regulator_enable(drvdata->regulator);
> > +	if (ret)
> > +		return ret;
> > +
> > +	ret = regmap_read(drvdata->regmap,
> >  			  SY7636A_REG_TERMISTOR_READOUT, &reg_val);  
> 
> Does that really work without delay ? Usually it takes some time for a chip
> to return useful data after its power supply has been enabled. calls
> 
Hmm, enabling the onoff bit behind the regulator is just needed to turn
ADC on here. But there is also the power good wait which should usually be enough.
Usually... But there is no guarantee. So yes, better wait for one adc aquisition.

Regards,
Andreas