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

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Date:   Thu, 17 Nov 2022 09:22:31 -0500
From:   William Breathitt Gray <william.gray@...aro.org>
To:     Michael Walle <michael@...le.cc>
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

On Wed, Nov 16, 2022 at 04:41:30PM +0100, Michael Walle wrote:
> 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

Currently, the 104-idi-48 module implements a get_direction() callback
that is executed in situations such as gpiod_get_direction() which
aren't necessarily related to sysfs. In this patch series, the
104-idi-48 module is migrated to the gpio_regmap API, but loses this
get_direction() support because it's an input-only configuration. The
purpose of this patch is to prevent that regression by supporting
get_direction() for input-only/output-only configurations.

William Breathitt Gray

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