linux-kernel - Re: [PATCH 1/4] hwmon (max6639): Use regmap

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Date: Mon, 22 Apr 2024 09:02:37 -0700
From: Guenter Roeck <linux@...ck-us.net>
To: Naresh Solanki <naresh.solanki@...ements.com>
Cc: krzysztof.kozlowski+dt@...aro.org, u.kleine-koenig@...gutronix.de,
	Jean Delvare <jdelvare@...e.com>, linux-hwmon@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] hwmon (max6639): Use regmap

On Mon, Apr 22, 2024 at 04:06:16PM +0530, Naresh Solanki wrote:
> Hi Guenter,
> 
> On Wed, 17 Apr 2024 at 02:55, Guenter Roeck <linux@...ck-us.net> wrote:
> >
> > On Tue, Apr 16, 2024 at 10:47:14PM +0530, Naresh Solanki wrote:
> > > Add regmap support.
> > >
> >
> > Missing (and not really utilizing) the benefits of using regmap.
> This is just replacing with regmap support
> >
> > > Signed-off-by: Naresh Solanki <naresh.solanki@...ements.com>
> > > ---
> > >  drivers/hwmon/Kconfig   |   1 +
> > >  drivers/hwmon/max6639.c | 157 ++++++++++++++++++++--------------------
> > >  2 files changed, 80 insertions(+), 78 deletions(-)
> > >
> > > diff --git a/drivers/hwmon/Kconfig b/drivers/hwmon/Kconfig
> > > index c89776d91795..257ec5360e35 100644
> > > --- a/drivers/hwmon/Kconfig
> > > +++ b/drivers/hwmon/Kconfig
> > > @@ -1223,6 +1223,7 @@ config SENSORS_MAX6621
> > >  config SENSORS_MAX6639
> > >       tristate "Maxim MAX6639 sensor chip"
> > >       depends on I2C
> > > +     select REGMAP_I2C
> > >       help
> > >         If you say yes here you get support for the MAX6639
> > >         sensor chips.
> > > diff --git a/drivers/hwmon/max6639.c b/drivers/hwmon/max6639.c
> > > index aa7f21ab2395..1af93fc53cb5 100644
> > > --- a/drivers/hwmon/max6639.c
> > > +++ b/drivers/hwmon/max6639.c
> > > @@ -20,6 +20,7 @@
> > >  #include <linux/err.h>
> > >  #include <linux/mutex.h>
> > >  #include <linux/platform_data/max6639.h>
> > > +#include <linux/regmap.h>
> > >
> > >  /* Addresses to scan */
> > >  static const unsigned short normal_i2c[] = { 0x2c, 0x2e, 0x2f, I2C_CLIENT_END };
> > > @@ -57,6 +58,8 @@ static const unsigned short normal_i2c[] = { 0x2c, 0x2e, 0x2f, I2C_CLIENT_END };
> > >
> > >  #define MAX6639_FAN_CONFIG3_THERM_FULL_SPEED 0x40
> > >
> > > +#define MAX6639_NDEV                         2
> > > +
> > >  static const int rpm_ranges[] = { 2000, 4000, 8000, 16000 };
> > >
> > >  #define FAN_FROM_REG(val, rpm_range) ((val) == 0 || (val) == 255 ? \
> > > @@ -67,7 +70,7 @@ static const int rpm_ranges[] = { 2000, 4000, 8000, 16000 };
> > >   * Client data (each client gets its own)
> > >   */
> > >  struct max6639_data {
> > > -     struct i2c_client *client;
> > > +     struct regmap *regmap;
> > >       struct mutex update_lock;
> > >       bool valid;             /* true if following fields are valid */
> > >       unsigned long last_updated;     /* In jiffies */
> > > @@ -95,9 +98,8 @@ struct max6639_data {
> > >  static struct max6639_data *max6639_update_device(struct device *dev)
> > >  {
> > >       struct max6639_data *data = dev_get_drvdata(dev);
> > > -     struct i2c_client *client = data->client;
> > >       struct max6639_data *ret = data;
> > > -     int i;
> > > +     int i, err;
> > >       int status_reg;
> > >
> > >       mutex_lock(&data->update_lock);
> > > @@ -105,39 +107,35 @@ static struct max6639_data *max6639_update_device(struct device *dev)
> >
> > Conversions to regmap should drop all local caching and use regmap
> > for caching (where appropriate) instead.
> max6639_update_device deals with volatile registers & caching isn't
> available for these.
> 

So ? Unless you replace caching (and accept that volatile registers
are not cached) I do not see the value of this patch. Replacing direct
chip accesses with regmap should have a reason better than "because".
Using regmap for caching would be a valid reason. At the same time,
the value of caching volatile registers is very much questionable.

Guenter