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

[Simon Glass]

Hi Przemyslaw,

On 23 February 2015 at 09:56, Przemyslaw Marczak <p.marczak at samsung.com> wrote:
> Hello,
>
>
> On 02/23/2015 04:30 PM, Simon Glass wrote:
>>
>> Hi,
>>
>> On 23 February 2015 at 03:51, Przemyslaw Marczak <p.marczak at samsung.com>
>> wrote:
>>>
>>>
>>> Hello Simon,
>>>
>>>
>>> On 02/20/2015 08:29 PM, Simon Glass wrote:
>>>>
>>>>
>>>> Hi,
>>>>
>>>> On 20 February 2015 at 10:50, Stephen Warren <swarren at wwwdotorg.org>
>>>> wrote:
>>>>>
>>>>>
>>>>> 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.
>>>>
>>>>
>>>>
>>>> We do currently use the GPIO to handle pullup/pulldown for some boards
>>>> so until we have a pinmux API (which might be a long while) it seems
>>>> reasonable for it to live there.
>>>>
>>>> If not, does anyone plan to write such an API?
>>>>
>>>
>>> Right, we uses this in most Exynos boards. But the boards uses direct
>>> calls to s5p gpio driver, without uclass.
>>> I wonder if wouldn't it be better and faster to leave the board low-level
>>> init routines as they are now.
>>>
>>>
>>>>>
>>>>>
>>>>>>>    > 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
>>>>
>>>>
>>>>
>>>> No this way lies madness. It is how things work on Jetson and Nyan.
>>>> Loads of opaque tables and no idea what the pins are connected to. It
>>>> has some value for pins that U-Boot doesn't use (so we are just
>>>> setting them up for Linux) but even then it is really opaque.
>>>>
>>>> We can't even sent patches to the file because it is auto-generated
>>>> from a tool in another repo. Tiny differences between boards are
>>>> hidden because we repeat all the information again with just a line or
>>>> two of changes. I really don't want exynos to go that way.
>>>>
>>>>> 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.
>>>>
>>>>
>>>>
>>>> This is like the 'funcmux' in Tegra I think. I think this is more
>>>> useful and we should use it to set up all peripheral pins. We can
>>>> review the code, see changes, understand what they relate to, etc.
>>>>
>>>> Anyway this all seems off-topic from this patch.
>>>>
>>>> Unless someone plans to write a pinmux subsystem for U-Boot (which I
>>>> agree would be better) I think the general approach of this patch is
>>>> good.
>>>>
>>>> Regards,
>>>> Simon
>>>>
>>>
>>> Ok, so there are two next versions of this patch-set.
>>> Please decide, which one is better.
>>>
>>> For me, at present, the current s5p_gpio api works fine for all the
>>> exynos based boards.
>>> Introducing the pinmux uclass is not a quick task, now I'm trying to
>>> focus on pmic.
>>
>>
>> OK, then I think we should probably leave it as it is. If we add
>> pull-ups to driver model it should be done with pinctl as Stephen
>> says. I doubt this is a huge task, since we can likely port over the
>> code from Linux. But for now I think we should keep with the s5p API
>> until someone takes on pinctl.
>>
>> Regards,
>> Simon
>>
>
> Great, in this case, can the v3 be accepted?

v3 of what please? Can you give me a pointer?

Regards,
Simon