linux-kernel - Re: [PATCH 3/3] mailbox: sunxi-msgbox: Add a new mailbox driver

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Date:   Wed, 28 Feb 2018 09:32:14 +0100
From:   Maxime Ripard <maxime.ripard@...tlin.com>
To:     Samuel Holland <samuel@...lland.org>
Cc:     Chen-Yu Tsai <wens@...e.org>,
        Jassi Brar <jassisinghbrar@...il.com>,
        Rob Herring <robh+dt@...nel.org>, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
        Andre Przywara <andre.przywara@....com>
Subject: Re: [PATCH 3/3] mailbox: sunxi-msgbox: Add a new mailbox driver

On Tue, Feb 27, 2018 at 08:27:14PM -0600, Samuel Holland wrote:
> +	/*
> +	 * The failure path should not disable the clock or assert the reset,
> +	 * because the PSCI implementation in firmware relies on this device
> +	 * being functional. Claiming the clock in this driver is required to
> +	 * prevent Linux from turning it off.
> +	 */
> +	ret = clk_prepare_enable(clk);
> +	if (ret) {
> +		dev_err(dev, "Failed to enable bus clock: %d\n", ret);
> +		return ret;
> +	}

You don't need it to be always on though. You only need it to be
enabled when you access the registers (on both sides I guess?). So you
could very well enable the clock in your registers accessors in Linux,
and do the same in the ARISC firmware. That should work.

Maxime

-- 
Maxime Ripard, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com

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