Re: [PATCH v3 10/16] gpio: add a reusable generic gpio_chip using regmap

Michael Walle
2020-05-25T10:20:39Z

Am 2020-05-25 11:05, schrieb Bartosz Golaszewski:
> wt., 12 maj 2020 o 16:41 Michael Walle <michael@walle.cc> napisał(a):
>>
>> >> +
>> >> +MODULE_AUTHOR("Michael Walle <michael@walle.cc>");
>> >> +MODULE_DESCRIPTION("GPIO generic regmap driver core");
>> >> +MODULE_LICENSE("GPL");
>> >> diff --git a/include/linux/gpio-regmap.h b/include/linux/gpio-regmap.h
>> >> new file mode 100644
>> >> index 000000000000..a868cbcde6e9
>> >> --- /dev/null
>> >> +++ b/include/linux/gpio-regmap.h
>> >> @@ -0,0 +1,69 @@
>> >> +/* SPDX-License-Identifier: GPL-2.0-only */
>> >> +
>> >> +#ifndef _LINUX_GPIO_REGMAP_H
>> >> +#define _LINUX_GPIO_REGMAP_H
>> >> +
>> >> +struct gpio_regmap;
>> >> +
>> >> +#define GPIO_REGMAP_ADDR_ZERO ((unsigned long)(-1))
>> >> +#define GPIO_REGMAP_ADDR(addr) ((addr) ? : GPIO_REGMAP_ADDR_ZERO)
>> >> +
>> >
>> > What if the addr is actually 0?
>>
>> Then the driver has to set GPIO_REGMAP_ADDR_ZERO or use the
>> convenience
>> macro GPIO_REGMAP_ADDR.
>>
>> So you can have
>>
>> struct gpio_regmap_config config = { 0 };
>> config.reg_dat_base = 0x10;
>> config.reg_dir_out_base = 0x20;
>>
>> or
>>
>> config.reg_dat_base = GPIO_REGMAP_ADDR_ZERO;
>>
>> or if you can't be sure if the RHS value might be zero:
>>
>> config.reg_dat_base = GPIO_REGMAP_ADDR(reg);
>>
>>
>> > Maybe drop GPIO_REGMAP_ADDR and require users to set unused registers
>> > to GPIO_REGMAP_ADDR_ZERO?
>>
>> Thats bad because:
>> * you'd have to set plenty of unused base registers for a simple
>> driver
>> * if there will be additional properties in the future, you have to
>> touch
>> all other drivers, because they are initialized as 0 (ie. valid
>> reg
>> 0).
>>
>> >> +/**
>> >> + * struct gpio_regmap_config - Description of a generic regmap
>> >> gpio_chip.
>> >> + *
>> >> + * @parent: The parent device
>> >> + * @regmap: The regmap used to access the registers
>> >> + * given, the name of the device is used
>> >> + * @label: (Optional) Descriptive name for GPIO
>> >> controller.
>> >> + * If not given, the name of the device is used.
>> >> + * @ngpio: Number of GPIOs
>> >> + * @reg_dat_base: (Optional) (in) register base address
>> >> + * @reg_set_base: (Optional) set register base address
>> >> + * @reg_clr_base: (Optional) clear register base address
>> >> + * @reg_dir_in_base: (Optional) out setting register base address
>> >> + * @reg_dir_out_base: (Optional) in setting register base address
>> >
>> > The two above are inverted I think?
>> good catch.
>>
>> > Also: why the limitation of only supporting one at a time?
>>
>> they should be exclusive, either you have a register where you set the
>> output bits to one, or the input bits. Maybe this need a bit more
>> context
>> above. in gpio-mmio.c you can set both and both are used in
>> set_direction(), but only one is read in get_direction().
>>
>> That being said, I have no strong opinion wether they should be
>> exclusive
>> or not, besides the symmetry of set_/get_direction().
>>
>> -michael
>>
>
> Sorry for the late response, your comments make sense to me. Are you
> going to submit a v4 before the v5.8 merge window?

I'm currently stuck with how to handle the MFD part. Ie. Rob doesn't
seem to like the logicial device numbering - or at least there wasn't
an answer to that one anymore, see patch 5/16.

If you like I could submit this patch on its own. But then there
wouldn't be a user for it.

-michael