linux-kernel - Re: [PATCH v2 2/2] gpio: pcf857x: add support for reset-gpios on (most) PCA967x

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Message-ID: <1947442.eGJsNajkDb@diego>
Date: Fri, 21 Feb 2025 14:48:55 +0100
From: Heiko Stübner <heiko@...ech.de>
To: Linus Walleij <linus.walleij@...aro.org>,
 Bartosz Golaszewski <brgl@...ev.pl>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>,
 Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>,
 Quentin Schulz <foss+kernel@...il.net>
Cc: linux-gpio@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, Quentin Schulz <quentin.schulz@...rry.de>
Subject:
 Re: [PATCH v2 2/2] gpio: pcf857x: add support for reset-gpios on (most)
 PCA967x

Am Freitag, 21. Februar 2025, 11:14:27 MEZ schrieb Quentin Schulz:
> From: Quentin Schulz <quentin.schulz@...rry.de>
> 
> The PCA9670, PCA9671, PCA9672 and PCA9673 all have a RESETN input pin
> that is used to reset the I2C GPIO expander.
> 
> One needs to hold this pin low for at least 4us and the reset should be
> finished after about 100us according to the datasheet[1]. Once the reset
> is done, the "registers and I2C-bus state machine will be held in their
> default state until the RESET input is once again HIGH.".
> 
> Because the logic is reset, the latch values eventually provided in the
> Device Tree via lines-initial-states property are inapplicable so they
> are simply ignored if a reset GPIO is provided.
> 
> [1] https://www.nxp.com/docs/en/data-sheet/PCA9670.pdf 8.5 and fig 22.
> 
> Tested-by: Heiko Stuebner <heiko@...ech.de> # RK3588 Tiger Haikou Video Demo
> Signed-off-by: Quentin Schulz <quentin.schulz@...rry.de>

Reviewed-by: Heiko Stuebner <heiko@...ech.de>