linux-kernel - Re: [PATCH v3] gpio: realtek-otto: switch to 32-bit I/O

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Date:   Mon, 22 Aug 2022 11:00:40 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Sander Vanheule <sander@...nheule.net>
Cc:     linux-gpio@...r.kernel.org, Bartosz Golaszewski <brgl@...ev.pl>,
        linux-kernel@...r.kernel.org,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Luiz Angelo Daros de Luca <luizluca@...il.com>,
        Birger Koblitz <mail@...ger-koblitz.de>,
        Jan Hoffmann <jan@....eu>, Paul Cercueil <paul@...pouillou.net>
Subject: Re: [PATCH v3] gpio: realtek-otto: switch to 32-bit I/O

On Sun, Aug 7, 2022 at 9:21 PM Sander Vanheule <sander@...nheule.net> wrote:

> By using 16-bit I/O on the GPIO peripheral, which is apparently not safe
> on MIPS, the IMR can end up containing garbage. This then results in
> interrupt triggers for lines that don't have an interrupt handler
> associated. The irq_desc lookup fails, and the ISR will not be cleared,
> keeping the CPU busy until reboot, or until another IMR operation
> restores the correct value. This situation appears to happen very
> rarely, for < 0.5% of IMR writes.
>
> Instead of using 8-bit or 16-bit I/O operations on the 32-bit memory
> mapped peripheral registers, switch to using 32-bit I/O only, operating
> on the entire bank for all single bit line settings. For 2-bit line
> settings, with 16-bit port values, stick to manual (un)packing.
>
> This issue has been seen on RTL8382M (HPE 1920-16G), RTL8391M (Netgear
> GS728TP v2), and RTL8393M (D-Link DGS-1210-52 F3, Zyxel GS1900-48).
>
> Reported-by: Luiz Angelo Daros de Luca <luizluca@...il.com> # DGS-1210-52
> Reported-by: Birger Koblitz <mail@...ger-koblitz.de> # GS728TP
> Reported-by: Jan Hoffmann <jan@....eu> # 1920-16G
> Fixes: 0d82fb1127fb ("gpio: Add Realtek Otto GPIO support")
> Signed-off-by: Sander Vanheule <sander@...nheule.net>
> Cc: Paul Cercueil <paul@...pouillou.net>

Reviewed-by: Linus Walleij <linus.walleij@...aro.org>

Yours,
Linus Walleij