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

Mon Feb 23 17:56:43 CET 2015

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?

Best regards,
-- 
Przemyslaw Marczak
Samsung R&D Institute Poland
Samsung Electronics
p.marczak at samsung.com