Re: [PATCH 1/2] gpio: regmap: Support few IC specific operations

[Matti Vaittinen <matti.vaittinen@xxxxxxxxxxxxxxxxx>]

On Thu, 2021-05-20 at 13:42 +0200, Michael Walle wrote:
> Hi Matti,
> 
> Am 2021-05-20 13:28, schrieb Matti Vaittinen:
> > The set_config and init_valid_mask GPIO operations are usually very
> > IC
> > specific. Allow IC drivers to provide these custom operations at
> > gpio-regmap registration.
> > 
> > Signed-off-by: Matti Vaittinen <matti.vaittinen@xxxxxxxxxxxxxxxxx>
> > ---
> >  drivers/gpio/gpio-regmap.c  | 49
> > +++++++++++++++++++++++++++++++++++++
> >  include/linux/gpio/regmap.h | 13 ++++++++++
> >  2 files changed, 62 insertions(+)
> > 
> > diff --git a/drivers/gpio/gpio-regmap.c b/drivers/gpio/gpio-
> > regmap.c
> > index 134cedf151a7..315285cacd3f 100644
> > --- a/drivers/gpio/gpio-regmap.c
> > +++ b/drivers/gpio/gpio-regmap.c
> > @@ -27,6 +27,10 @@ struct gpio_regmap {
> >  	int (*reg_mask_xlate)(struct gpio_regmap *gpio, unsigned int
> > base,
> >  			      unsigned int offset, unsigned int *reg,
> >  			      unsigned int *mask);
> > +	int (*set_config)(struct regmap *regmap, void *drvdata,
> > +			  unsigned int offset, unsigned long config);
> > +	int (*init_valid_mask)(struct regmap *regmap, void *drvdata,
> > +				unsigned long *valid_mask, unsigned int
> > ngpios);
> 
> Maybe we should also make the first argument a "struct gpio_regmap"
> and provide a new gpio_regmap_get_regmap(struct gpio_regmap). Thus
> having a similar api as for the reg_mask_xlate(). Andy?

I don't really see the reason of making this any more complicated for
IC drivers. If we don't open the struct gpio_regmap to IC drivers -
then they never need the struct gpio_regmap pointer itself but each IC
driver would need to do some unnecessary function call
(gpio_regmap_get_regmap() in this case). I'd say that would be
unnecessary bloat.

> 
> >  	void *driver_data;
> >  };
> > @@ -39,6 +43,43 @@ static unsigned int gpio_regmap_addr(unsigned
> > int 
> > addr)
> >  	return addr;
> >  }
> > 
> > +static int regmap_gpio_init_valid_mask(struct gpio_chip *gc,
> > +					unsigned long *valid_mask,
> > +					unsigned int ngpios)
> > +{
> > +	struct gpio_regmap *gpio;
> > +	void *drvdata;
> > +
> > +	gpio = gpiochip_get_data(gc);
> > +
> > +	if (!gpio->init_valid_mask) {
> > +		WARN_ON(!gpio->init_valid_mask);
> > +		return -EINVAL;
> > +	}
> 
> Why not the following?
> 
> if (!gpio->init_valid_mask)
>      return 0;

It just feels like an error if regmap_gpio_init_valid_mask() is ever
called by core without having the gpio->init_valid_mask set. Probably
this would mean that the someone has errorneously modified the gpio-
>init_valid_mask set after gpio_regmap registration - whih smells like
a problem. Thus the WARN() sounds like a correct course of action to
me. (I may be wrong though - see below)

> Thus copying the behavior of gpiolib.

I must admit I didn't check how this is implemented in gpiolib. But the
gpio_chip's init_valid_mask should not be set if regmap_gpio_config
does not have valid init_valid_mask pointer at registration. Thus it
smells like an error to me if the GPIO core calls the
regmap_gpio_init_valid_mask() and regmap_gpio has not set the
init_valid_mask pointer. But as I said, I haven't looked in gpiolib for
this so I may be wrong.

> 
> > +
> > +	drvdata = gpio_regmap_get_drvdata(gpio);
> > +
> > +	return gpio->init_valid_mask(gpio->regmap, drvdata,
> > valid_mask, 
> > ngpios);
> > +}
> > +
> > +static int gpio_regmap_set_config(struct gpio_chip *gc, unsigned
> > int 
> > offset,
> > +				  unsigned long config)
> > +{
> > +	struct gpio_regmap *gpio;
> > +	void *drvdata;
> > +
> > +	gpio = gpiochip_get_data(gc);
> > +
> > +	if (!gpio->set_config) {
> > +		WARN_ON(!gpio->set_config);
> > +		return -EINVAL;
> > +	}
> 
> same here, return -ENOTSUPP.

As above - 
if (!gpio->set_config) {
	the gpio-core should never call gpio_regmap_set_config() if the
}

Maybe I should add a comment to clarify the WARN() ?
> 
> > +
> > +	drvdata = gpio_regmap_get_drvdata(gpio);
> > +
> > +	return gpio->set_config(gpio->regmap, drvdata, offset, config);
> > +}
> > +
> >  static int gpio_regmap_simple_xlate(struct gpio_regmap *gpio,
> >  				    unsigned int base, unsigned int
> > offset,
> >  				    unsigned int *reg, unsigned int
> > *mask)
> > @@ -235,6 +276,8 @@ struct gpio_regmap *gpio_regmap_register(const
> > struct gpio_regmap_config *config
> >  	gpio->reg_clr_base = config->reg_clr_base;
> >  	gpio->reg_dir_in_base = config->reg_dir_in_base;
> >  	gpio->reg_dir_out_base = config->reg_dir_out_base;
> > +	gpio->set_config = config->set_config;
> > +	gpio->init_valid_mask = config->init_valid_mask;
> > 
> >  	/* if not set, assume there is only one register */
> >  	if (!gpio->ngpio_per_reg)
> > @@ -253,6 +296,10 @@ struct gpio_regmap *gpio_regmap_register(const
> > struct gpio_regmap_config *config
> >  	chip->ngpio = config->ngpio;
> >  	chip->names = config->names;
> >  	chip->label = config->label ?: dev_name(config->parent);
> > +	if (gpio->set_config)
> > +		chip->set_config = gpio_regmap_set_config;
> > +	if (gpio->init_valid_mask)
> > +		chip->init_valid_mask = regmap_gpio_init_valid_mask;
> > 
> >  #if defined(CONFIG_OF_GPIO)
> >  	/* gpiolib will use of_node of the parent if chip->of_node is
> > NULL */
> > @@ -280,6 +327,8 @@ struct gpio_regmap *gpio_regmap_register(const
> > struct gpio_regmap_config *config
> >  		chip->direction_output = gpio_regmap_direction_output;
> >  	}
> > 
> > +	gpio_regmap_set_drvdata(gpio, config->drvdata);
> 
> I'm wondering if we need the gpio_regmap_set_drvdata() anymore or if
> we can just drop it entirely.

I wouldn't drop it. I think there _may_ be cases where the drvdata is
set only after the registration. (Just my gut-feeling, I may be wrong
though)


Best Regards
	Matti Vaittinen

-- 
Matti Vaittinen, Linux device drivers
ROHM Semiconductors, Finland
SWDC
Kiviharjunlenkki 1E
90220 OULU
FINLAND

~~~ "I don't think so," said Rene Descartes. Just then he vanished ~~~

Simon says - in Latin please.
"non cogito me" dixit Rene Descarte, deinde evanescavit

(Thanks for the translation Simon)