Re: RFC: gpio: mmio: add support for 3 direction regs

From: Vladimir Zapolskiy
Date: Thu Jan 03 2019 - 03:59:18 EST

On 01/03/2019 10:51 AM, Fried, Ramon wrote:
> On 1/3/2019 10:07, Vladimir Zapolskiy wrote:
>> Hi Ramon,
>> On 01/03/2019 09:36 AM, Fried, Ramon wrote:
>>> Hi.
>>> I'm working on a driver for STA2X11 GPIO controller who seems to fit
>>> best to the generic mmio driver,
>> I hope you have seen the existing driver drivers/gpio/gpio-sta2x11.c
> I surely did. we have the same IP in our soc but it was changed a lot
> internally, don't want to litter the original.
>>> the only problem I have is with the dir register case. The STA2X11
>>> has 3 registers for dir, one for data, one for set and one for
>>> clear. The generic-mmio driver has support for this fashion for the
>>> dat & set & clear registers but not for dirout/dirin registers.
>>> I wonder if support for this is generic enough to deserve a patch, if
>>> so I'm willing to quickly add this support, if not, adding a flag
>>> such as below, will allow partly using the generic mmio driver only
>>> for set/get and the direction can be handled outside the driver.
>> If gpio-mmio fits well, then it might be simpler to set a flag
>> BGPIOF_UNREADABLE_REG_DIR, then call bgpio_init() and then overwrite
>> .direction_input, .direction_output and .get_direction callbacks,
>> as a reference you can take a look at gpio-74xx-mmio.c
> Nice.
> That's an option I didn't think of, better than setting the flag.
> what about adding the generic support ?

Setting a GPIO direction over three different registers doesn't sound
as a suitable candidate for generalization, also your particular
implementation is partial, relies on external platform/driver code
to preset the directions and it does not allow to change direction
in runtime, so just renounce the idea.

Best wishes,