linux-kernel - Re: gpio: gpio-pci-idio-16 regression after LTS upgrade

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Message-Id: <DDHX9YA0ZMKO.C1MA3CHLT4ZZ@kernel.org>
Date: Tue, 14 Oct 2025 11:03:25 +0200
From: "Michael Walle" <mwalle@...nel.org>
To: "William Breathitt Gray" <wbg@...nel.org>, "Mark Cave-Ayland"
 <mark.caveayland@...anix.com>
Cc: <linus.walleij@...aro.org>, <brgl@...ev.pl>,
 <andriy.shevchenko@...ux.intel.com>, <broonie@...nel.org>,
 <linux-gpio@...r.kernel.org>, <linux-kernel@...r.kernel.org>, "Ioana
 Ciornei" <ioana.ciornei@....com>
Subject: Re: gpio: gpio-pci-idio-16 regression after LTS upgrade

Hi,

On Thu Oct 9, 2025 at 11:49 AM CEST, William Breathitt Gray wrote:
> On Thu, Oct 09, 2025 at 10:05:58AM +0100, Mark Cave-Ayland wrote:
>> On 07/10/2025 09:16, William Breathitt Gray wrote:
>> > So the intention I had with gpio-idio-16 was to provide reg_dat_base and
>> > reg_set_base to define the input and output bases, and then
>> > reg_mask_xlate would do the translation between input and outputs. I
>> > think this design is allowed by gpio-regmap, is it not Michael?
>> >
>> > In theory, gpio_regmap_get_direction should call gpio->reg_mask_xlate()
>> > which is mapped to idio_16_reg_mask_xlate(), and thus set reg and mask
>> > which then is evaluated at the end of gpio_regmap_get_direction() to
>> > determine which direction to return.
>> >
>> > Is it possible idio_16_reg_mask_xlate() is returning the wrong values
>> > for reg and mask?
>> >
>> > William Breathitt Gray
>> 
>> The only logic around .reg_dat_base and .reg_set_base in
>> gpio_regmap_get_direction() is this:
>> 
>> 	if (gpio->reg_dat_base && !gpio->reg_set_base)
>> 		return GPIO_LINE_DIRECTION_IN;
>> 	if (gpio->reg_set_base && !gpio->reg_dat_base)
>> 		return GPIO_LINE_DIRECTION_OUT;
>> 
>> Otherwise it attempts to use .reg_dir_out_base and .reg_dir_in_base
>> which are not set for gpio-idio-16 because the GPIO directions are fixed
>> and not controlled via a data-direction register. And as these are not
>> set, gpio_regmap_get_direction() returns -ENOTSUPP.
>> 
>> Were you thinking that gpio_regmap_get_direction() should have some
>> additional direction logic if both .reg_dat_base and .reg_set_base are
>> set, based upon their comparative values?
>
> Ah you're right, I misunderstood the logic in gpio_regmap_get_direction.
> So essentially the problem is that gpio-idio-16 has no way of indicating
> the direction of its I/O because it's mixed.
>
> The IDIO-16 series lacks a direction setting register, so I think the
> proper solution is as you suggest: add support for a get_direction
> callback to struct gpio_regmap_config in the same vein as the existing
> reg_mask_xlate callback. Then in gpio_regmap_register you can set
> gpio->get_direction = config->get_direction in the same way
> config->reg_mask_xlate is handled.

IIUC the chip has fixed input and outputs. In that case this should
help:
https://lore.kernel.org/all/20250922142427.3310221-8-ioana.ciornei@nxp.com/

I guess Ioana will resubmit the series for this cycle. To fix the
regression, I guess the patch can then be picked up by the stable
team along with the driver patch which will set the
.fixed_direction_output config field.

-michael

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