linux-kernel - Re: [PATCH v2 1/4] gpio: regmap: Always set gpio_chip get

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Date:   Wed, 16 Nov 2022 16:41:30 +0100
From:   Michael Walle <michael@...le.cc>
To:     William Breathitt Gray <william.gray@...aro.org>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        robert.marko@...tura.hr, linus.walleij@...aro.org, brgl@...ev.pl,
        linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org,
        broonie@...nel.org
Subject: Re: [PATCH v2 1/4] gpio: regmap: Always set gpio_chip get_direction

Am 2022-11-13 14:21, schrieb William Breathitt Gray:
> On Sun, Nov 13, 2022 at 02:40:17PM +0200, Andy Shevchenko wrote:
>> On Thu, Nov 10, 2022 at 08:55:50PM -0500, William Breathitt Gray 
>> wrote:
>> > If you only have reg_dat_base set, then it is input-only; if you only
>> > have reg_set_base set, then it is output-only. Thus, we can always set
>> > gpio_chip get_direction to gpio_regmap_get_direction and return
>> > GPIO_LINE_DIRECTION_IN/GPIO_LINE_DIRECTION_OUT given the respective
>> > register base addresses configuration.
>> 
>> Seems legit to me. Have you checked if we have any gpio-regmap drivers 
>> that
>> have something like this in their configuration already? In such cases 
>> we need
>> to be sure they behave as expected.
>> 
>> From the code perspective:
>> Reviewed-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> 
> I see gpio-sl28cpld has two device types SL28CPLD_GPO (output-only) and
> SL28CPLD_GPI (input-only); gpio-tn48m similarly has two device types
> TN48M_GPO (output-only) and TN48M_GPI (input-only). It doesn't look 
> like
> the change in this patch will cause problems for them, but I'll let
> Michael Walle and Robert Marko comment if they see issues here.

For the sl28cpld driver this shouldn't be a problem. So for that
Acked-by: Michael Walle <michael@...le.cc>

But back when I wrote gpio-regmap the bgpio served as a blue print.
There is the same handling. If you look at gpiolib-sysfs.c there
is a comment about the direction property:

  * MAY BE OMITTED if kernel won't allow direction changes

So from a gpiolib/sysfs POV I'm not sure about this change. Does
get_direction == NULL means setting the direction isn't possible?
OTHO there is a fat "MAY" :)

Which brings me to the question of "why this change?". The commit
message doesn't mention it. Just out of curiosity.

-michael