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

[Simon Glass]

Hi Masahiro,

On 6 July 2015 at 11:20, Masahiro Yamada <yamada.masahiro at socionext.com> wrote:
> Hi Simon,
>
>
>
> 2015-07-07 1:39 GMT+09:00 Simon Glass <sjg at chromium.org>:
>> 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.
>
>
> As you may already know, in Linux, GPIO numbers are mapped into pin numbers
> via "gpio-ranges" property, but we need much effort
> to implement the framework in U-Boot.
>
> Do you think it would make sense to support full-spec pinctrl drivers
> (much closer to Linux's one) in U-Boot?   Or is it crazy?

We can do - it's not that hard. The pinctrl patch I sent is more
low-spec. But we can expand it later.

>
> I just skimmed over your pinctrl patches, but
> I could not understand fully how it works.  (especially, .get_periph_id).

The idea is that in U-Boot it is convenient to reference peripherals
with an ID, which we can use to set up a clock, or pinmux. So we want
to find out the ID for a device.

>
>
> I will leave some comments on your rockchip pinctrl patch.

OK thanks.

Regards,
Simon