linux-kernel - Re: [PATCH 3/4] clk: bcm2835: Add support for programming the audio domain clocks.

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Date:	Thu, 10 Sep 2015 14:35:10 -0700
From:	Eric Anholt <eric@...olt.net>
To:	linux-clk@...r.kernel.org
Cc:	linux-arm-kernel@...ts.infradead.org,
	linux-rpi-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Stephen Warren <swarren@...dotorg.org>,
	Lee Jones <lee@...nel.org>,
	Stephen Boyd <sboyd@...eaurora.org>,
	Mike Turquette <mturquette@...aro.org>,
	devicetree@...r.kernel.org
Subject: Re: [PATCH 3/4] clk: bcm2835: Add support for programming the audio domain clocks.

Eric Anholt <eric@...olt.net> writes:

> This adds support for enabling, disabling, and setting the rate of the
> audio domain clocks.  It will be necessary for setting the pixel clock
> for HDMI in the VC4 driver and let us write a cpufreq driver.  It will
> also improve compatibility with user changes to the firmware's
> config.txt, since our previous fixed clocks are unaware of it.
>
> The firmware also has support for configuring the clocks through the
> mailbox channel, but the pixel clock setup by the firmware doesn't
> work, and it's Raspberry Pi specific anyway.  The only conflicts we
> should have with the firmware would be if we made firmware calls that
> result in clock management (like opening firmware V3D or ISP access,
> which we don't support in upstream), or on hardware over-thermal or
> under-voltage (when the firmware would rewrite PLLB to take the ARM
> out of overclock).  If that happens, our cached .recalc_rate() results
> would be incorrect, but that's no worse than our current state where
> we used fixed clocks.
>
> The existing fixed clocks in the code are left in place to provide
> backwards compatibility with old device tree files.
>
> Signed-off-by: Eric Anholt <eric@...olt.net>
> ---

> +	onecell->clk_num = BCM2835_CLOCK_COUNT;
> +	onecell->clks = kzalloc(sizeof(*onecell->clks), GFP_KERNEL);

Review of another clock driver I wrote pointed out that I missed the
multiply by BCM2835_CLOCK_COUNT here.  I'll send an updated version.

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