linux-kernel - Re: [PATCH v2] gpio: ts4900: Do not set DAT and OE together

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Date:   Thu, 10 Mar 2022 13:26:56 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Kris Bahnsen <kris@...eddedts.com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <brgl@...ev.pl>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Mark Featherston <mark@...eddedts.com>
Subject: Re: [PATCH v2] gpio: ts4900: Do not set DAT and OE together

Bart, side note: I can't see your for-current in Linux Next for a few
days, is everything okay?

On Wed, Mar 9, 2022 at 1:47 AM Kris Bahnsen <kris@...eddedts.com> wrote:
>
> From: Mark Featherston <mark@...eddedTS.com>
>
> This works around an issue with the hardware where both OE and
> DAT are exposed in the same register. If both are updated
> simultaneously, the harware makes no guarantees that OE or DAT

hardware

the OE

> will actually change in any given order and may result in a
> glitch of a few ns on a GPIO pin when changing direction and value
> in a single write.
>
> Setting direction to input now only affects OE bit. Setting

the OE bit

> direction to output updates DAT first, then OE.
>
> Fixes: 9c6686322d74 ("gpio: add Technologic I2C-FPGA gpio support")

>

There must be no blank lines in the tag block.

> Signed-off-by: Mark Featherston <mark@...eddedTS.com>
> Signed-off-by: Kris Bahnsen <kris@...eddedTS.com>

...

> + * Copyright (C) 2015-2018 Technologic Systems

Not sure it's a valid change for a simple fix.

...

> -       /*
> -        * This will clear the output enable bit, the other bits are
> -        * dontcare when this is cleared
> +       /* Only clear the OE bit here, requires a RMW. Prevents potential issue
> +        * with OE and data getting to the physical pin at different times.
>          */

Keep the proper style for multi-line comments.

...

> +       /* If changing from an input to an output, we need to first set the
> +        * proper data bit to what is requested and then set OE bit. This

the OE bit

> +        * prevents a glitch that can occur on the IO line
> +        */

Keep the proper style.

-- 
With Best Regards,
Andy Shevchenko