Re: [PATCH v2 resend 1/2] gpio: tps68470: Fix tps68470_gpio_get() reading from the wrong register

[Hans de Goede <hdegoede@redhat.com>]

Hi,

On 1/25/23 12:23, Andy Shevchenko wrote:
> On Wed, Jan 25, 2023 at 1:05 PM Hans de Goede <hdegoede@redhat.com> wrote:
>>
>> For the regular GPIO pins the value should be read from TPS68470_REG_GPDI,
>> so that the actual value of the pin is read, rather than the value the pin
>> would output when put in output mode.
> 
> It really depends. I think it's a wrong perception and brings nothing
> to software. If we output, we know what we program, so reading back
> returns us what we _assume_ should be on the pin under normal
> circumstances. The difference is OD/OS/OE/OC cases where we output
> only one possible value.
> 
>> Fixes: 275b13a65547 ("gpio: Add support for TPS68470 GPIOs")
> 
> Is it really fixing anything? Can we have more?
> 
> P.S. Before doing this, I would have a clarification in the
> documentation. Sorry that I have had no time to respond to my series
> regarding that. But it seems we have a strong disagreement in the
> area.

I know disagree on some of the semantics of gpiod_get_value() but 99.9%
of the consumers of gpiod_get_value() are going to deal with pins
which are either in input mode, or in some non push-pull (e.g.
open-collector for i2c) mode. And in those cases reading GPDI
os the right thing to do.

Calling gpiod_get_value() when the pin is in push-pull mode really
does not make much sense, so there will be very little if any users
of that. And this patch fixes the 99.9% other (potential) users
while not breaking the push-pull case since even then reading GPDI
should still return the right value.

Regards,

Hans