linux-kernel - Re: [PATCH 1/9] pinctrl: sunxi: Support I/O bias voltage setting on A80

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Date:   Wed, 6 Feb 2019 13:17:18 +0100
From:   Maxime Ripard <maxime.ripard@...tlin.com>
To:     Chen-Yu Tsai <wens@...e.org>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        linux-arm-kernel@...ts.infradead.org, linux-gpio@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-sunxi@...glegroups.com
Subject: Re: [PATCH 1/9] pinctrl: sunxi: Support I/O bias voltage setting on
 A80

On Wed, Feb 06, 2019 at 11:32:31AM +0800, Chen-Yu Tsai wrote:
> The A80 SoC has configuration registers for I/O bias voltage. Incorrect
> settings would make the affected peripherals inoperable in some cases,
> such as Ethernet RGMII signals biased at 2.5V with the settings still
> at 3.3V. However low speed signals such as MDIO on the same group of
> pins seem to be unaffected.
> 
> Previously there was no way to know what the actual voltage used was,
> short of hard-coding a value in the device tree. With the new pin bank
> regulator supply support in place, the driver can now query the
> regulator for its voltage, and if it's valid (as opposed to being the
> dummy regulator), set the bias voltage setting accordingly.
> 
> Add a quirk to denote the presence of the configuration registers, and
> a function to set the correct setting based on the voltage read back
> from the regulator.
> 
> This is only done when the regulator is first acquired and enabled.
> While it would be nice to have a notifier on the regulator so that when
> the voltage changes, the driver can update the setting, in practice no
> board currently supports dynamic changing of the I/O voltages.
> 
> Signed-off-by: Chen-Yu Tsai <wens@...e.org>

Acked-by: Maxime Ripard <maxime.ripard@...tlin.com>

Maxime

-- 
Maxime Ripard, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

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