[U-Boot] [PATCH 1/4] dm: gpio: extend gpio api by dm_gpio_set_pull()

[Stephen Warren]

On 02/20/2015 02:34 AM, Przemyslaw Marczak wrote:
> Hello,
>
> On 02/19/2015 06:09 PM, Stephen Warren wrote:
>> On 02/19/2015 05:11 AM, Przemyslaw Marczak wrote:
>>> Hello,
>>>
>>> On 02/18/2015 05:39 PM, Stephen Warren wrote:
>>>> On 02/17/2015 10:01 PM, Simon Glass wrote:
>>>>> +Stephen who might have an opinion on this.
>>>>>
>>>>> Hi Przemyslaw,
>>>>>
>>>>> On 17 February 2015 at 06:09, Przemyslaw Marczak
>>>>> <p.marczak at samsung.com> wrote:
>>>>>> This commits extends:
>>>>>> - dm gpio ops by: 'set_pull' call
>>>>>> - dm gpio uclass by: dm_gpio_set_pull() function
>>>>>>
>>>>>> The pull mode is not defined so should be driver specific.
>>>>>
>>>>> It's good to implement this, but I think you should try to have a
>>>>> standard interface. You could define the options you want to support
>>>>> and pass in a standard value.
>>>>>
>>>>> Otherwise we are not really providing a driver abstraction, only an
>>>>> interface.
>>>>
>>>> I don't think that pull is a GPIO-related function/property. At
>>>> least on
>>>> Tegra, the GPIO controller allows you to set the pin direction and the
>>>> output value and that's it. Configuring pull-up/down and other IO
>>>> related properties is done in the pinmux controller instead. I don't
>>>> think we want a standard API that has to touch both HW modules at once.
>>>> What common code needs to manipulate a GPIO's pull-up/down setting? As
>>>> precedent observe that pull-up/down isn't part of the Linux kernel's
>>>> GPIO API, but rather that's part of the SoC-specific pinctrl driver,
>>>> which controls pinmuxing etc.
>>>>
>>>
>>> This is a quite different than in the Exynos, where all the gpio
>>> functions and properties can be set by few registers within range of
>>> each gpio port base address. So in this case we don't touch another
>>> hardware module, we modify one of available gpio related registers.
>>>
>>> Anyway, if we want to have a single and common gpio API in the future,
>>> then I think it is better to add pull option.
>>
>> Why? I'll ask again: What common driver code needs to manipulate
>> pull-ups?
>
> Please look at driver: drivers/gpio/s5p_gpio.c
>
> It's one driver related to one gpio hardware submodule and it takes care
> about standard gpio properties and also mux/pull/drv/rate.
>
> And the exynos pinmux code is only a software abstraction:
> arch/arm/cpu/armv7/exynos/pinmux.c

I didn't want to ask which driver implements the control of pullups, but 
rather which other driver needs to turn pullups on/off in a standard way 
across multiple SoCs.

In other words, do you expect code in common/ to need to call a "set pin 
pullup" function? If so, then we certainly need a standard API to 
manipulate pullups. However if no common code needs to manipulate 
pullups, then I'd argue we don't actually need a common API to do this, 
since there's no code that would call that common API.

>>  > And the driver will
>>> implement what is required, instead of provide common and private api
>>> for each driver.
>>
>> I'm not proposing driver-specific APIs, but rather having a common GPIO
>> API and a common pinmux API. They need to be different since different
>> HW modules may implement the functionality.
>>
>
> As in the above example, for the Exynos it's the one hw module, so it's
> simply.
>
>>> For the various devices it is unclear, what should be pinmux and what
>>> should be gpio driver.
>>
>> How about the following are GPIO:
>> * Set GPIO pin direction
>> * Read GPIO input
>> * Set GPIO output value
>>
>> ... and anything else is pinmux. That's the split in Linux and AFAIK it
>> works out fine.
>>
>> It'd be perfectly fine for the same driver code to implement both a GPIO
>> and a pinmux driver, if the HW supports it.
>>
>
> Ok, I can drop this commit, since the current code works fine.
>
>>> Moreover in my opinion from the single external pin point of view the
>>> pull up/down is the property of that pin.
>>
>> It's a property of the same pin, but semantically it's not manipulating
>> a GPIO-related function.
>>
>>> Actually for Exynos, the pinmux is an abstraction and uses only GPIO
>>> driver api in U-Boot.
>>>
>>> Do we need pinmux class?
>>>
>>> Best regards,
>>
>>
>
> As I wrote in one of my previous e-mail, I was testing eMMC detect.
> And setting the pull was required for this, before call the pinmux for
> eMMC pins.
> But finally the eMMC detect seem to be not useful in case of the present
> 'mmc rescan' command.

Why wouldn't the pinmux driver for the whole system simply apply the 
board's whole pinmux configuration before initializing any IO controller 
drivers? IO controller drivers shouldn't have to initialize 
board-/SoC-specific pinmux, but the board-/SoC-specfic code should do so.

At most, the eMMC driver should call a function such as pinmux_emmc(), 
and the board/SoC code should implement that as appropriate for that 
board. The eMMC driver shouldn't have to know about applying specific 
pullups/downs to specific pins (since those settings and pins are likely 
board-/SoC-specific, and drivers shouldn't know about 
board-/SoC-specific details). The only exception would be if the 
standard IO protocol requires pullups to be changed during regular 
operation. In which case, a specific callback from the driver could be 
added for each protocol-mandated configuration change, thus keeping the 
IO controller driver still completely isolated from details of the pins 
and pinmux APIs etc.