[U-Boot] [PATCH 19/55] dm: gpio: Add support for setting a GPIO's pull direction

[Simon Glass]

Hi Masahiro,

On 4 July 2015 at 22:55, Masahiro Yamada <yamada.masahiro at socionext.com> wrote:
> Hi Simon,
>
>
> 2015-07-03 9:15 GMT+09:00 Simon Glass <sjg at chromium.org>:
>> At present the driver model GPIO API does not support pull-up/pull-down on
>> input GPIOs. This is required in some cases.
>>
>> Add this feature to the API with two new methods that drivers can optionally
>> implement.
>>
>> Signed-off-by: Simon Glass <sjg at chromium.org>
>> ---
>>
>>  drivers/gpio/gpio-uclass.c | 31 +++++++++++++++++++++++++++++++
>>  include/asm-generic/gpio.h | 46 ++++++++++++++++++++++++++++++++++++++++++++++
>>  2 files changed, 77 insertions(+)
>>
>> diff --git a/drivers/gpio/gpio-uclass.c b/drivers/gpio/gpio-uclass.c
>> index 4efda31..c4ba580 100644
>> --- a/drivers/gpio/gpio-uclass.c
>> +++ b/drivers/gpio/gpio-uclass.c
>> @@ -374,6 +374,37 @@ int dm_gpio_set_dir(struct gpio_desc *desc)
>>         return dm_gpio_set_dir_flags(desc, desc->flags);
>>  }
>>
>> +int dm_gpio_set_pull(struct gpio_desc *desc, enum gpio_pull pull)
>> +{
>> +       struct dm_gpio_ops *ops = gpio_get_ops(desc->dev);
>> +       int ret;
>> +
>> +       ret = check_reserved(desc, "set_pull");
>> +       if (ret)
>> +               return ret;
>> +
>> +       if (!ops->set_pull)
>> +               return -ENOSYS;
>> +
>> +       return ops->set_pull(desc->dev, desc->offset, pull);
>> +}
>> +
>> +int dm_gpio_get_pull(struct gpio_desc *desc, unsigned offset)
>> +{
>> +       struct dm_gpio_ops *ops = gpio_get_ops(desc->dev);
>> +       int ret;
>> +
>> +       ret = check_reserved(desc, "get_pull");
>> +       if (ret)
>> +               return ret;
>> +
>> +       if (!ops->get_pull)
>> +               return -ENOSYS;
>> +
>> +       return ops->get_pull(desc->dev, desc->offset);
>> +}
>> +
>> +
>>  /**
>>   * gpio_get_value() - [COMPAT] Sample GPIO pin and return it's value
>>   * gpio:       GPIO number
>> diff --git a/include/asm-generic/gpio.h b/include/asm-generic/gpio.h
>> index 0af599f..db5504f 100644
>> --- a/include/asm-generic/gpio.h
>> +++ b/include/asm-generic/gpio.h
>> @@ -126,6 +126,13 @@ struct gpio_desc {
>>          */
>>  };
>>
>> +/* GPIO pull directions (used for input lines) */
>> +enum gpio_pull {
>> +       GPIO_PULL_NONE,
>> +       GPIO_PULL_DOWN,
>> +       GPIO_PULL_UP,
>> +};
>> +
>>  /**
>>   * dm_gpio_is_valid() - Check if a GPIO is valid
>>   *
>> @@ -276,6 +283,26 @@ struct dm_gpio_ops {
>>          */
>>         int (*xlate)(struct udevice *dev, struct gpio_desc *desc,
>>                      struct fdtdec_phandle_args *args);
>> +
>> +       /**
>> +        * set_pull() - set pull direction
>> +        *
>> +        * @dev:        Device to adjust
>> +        * @offset:     GPIO offset within device
>> +        * @pull:       New pull direction
>> +        * @return 0 if OK, -ve on error
>> +        */
>> +       int (*set_pull)(struct udevice *dev, unsigned offset,
>> +                       enum gpio_pull pull);
>> +
>> +       /**
>> +        * get_pull() - get pull direction
>> +        *
>> +        * @dev:        Device to check
>> +        * @offset:     GPIO offset within device
>> +        * @return current pull direction or -ve on error
>> +        */
>> +       int (*get_pull)(struct udevice *dev, unsigned offset);
>>  };
>>
>
>
> Do you want to control pull-up/down only for GPIOs?
> Pin-biasing makes sense for dedicated functions as well as GPIOs.
> At least, I am inclined to enable pull-up registers for SCL/SDA (I2C)
> pins on my boards.
>
> As far as I know, in Linux, such stuff is handled in pinctrl drivers.
> I see no .set_pull() callback in struct gpio_chip in Linux.
>
> As far as I see your pinctrl implementation,
> (http://patchwork.ozlabs.org/patch/487801/)
> it looks like "pinctrl = pinmuxing" in U-Boot, whereas "pinctrl =
> pinmuxing + pin-configuration" in Linux.

That's true, but still it is useful to be able to set pull direction
for GPIOs. I did sent a pinctrl uclass patch recently. Perhaps we
could add a new function there. But how would we identify which pin to
change? The GPIO pin name is convenient but may not be available in
the pinctrl driver, since this adds a lot of size to the device tree.

Regards,
Simon