linux-kernel - Re: [PATCH 19/19] Documentation: ACPI for ARM64

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Date:	Wed, 20 Aug 2014 11:42:27 -0500
From:	Grant Likely <grant.likely@...aro.org>
To:	Hanjun Guo <hanjun.guo@...aro.org>,
	Catalin Marinas <catalin.marinas@....com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Mark Rutland <mark.rutland@....com>
Cc:	Graeme Gregory <graeme.gregory@...aro.org>,
	Arnd Bergmann <arnd@...db.de>,
	Sudeep Holla <Sudeep.Holla@....com>,
	Will Deacon <will.deacon@....com>,
	Jason Cooper <jason@...edaemon.net>,
	Marc Zyngier <marc.zyngier@....com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Mark Brown <broonie@...aro.org>,
	Robert Richter <rric@...nel.org>,
	Lv Zheng <lv.zheng@...el.com>,
	Robert Moore <robert.moore@...el.com>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Liviu Dudau <Liviu.Dudau@....com>,
	Randy Dunlap <rdunlap@...radead.org>,
	Charles.Garcia-Tobin@....com, linux-acpi@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linaro-acpi-private@...aro.org, Hanjun Guo <hanjun.guo@...aro.org>
Subject: Re: [PATCH 19/19] Documentation: ACPI for ARM64

On Thu, 24 Jul 2014 21:00:25 +0800, Hanjun Guo <hanjun.guo@...aro.org> wrote:
> +Clocks
> +------
> +
> +Like clocks that are part of the power resources there is no standard way
> +to represent a clock tree in ACPI 5.1 in a similar manner to how it is
> +described in DT.
> +
> +Devices affected by this include things like UARTs, SoC driven LCD displays,
> +etc.
> +
> +The firmware for example UEFI should initialise these clocks to fixed working
> +values before the kernel is executed. If a driver requires to know rates of
> +clocks set by firmware then they can be passed to kernel using _DSD.
> +
> +example :-
> +
> +Device (CLK0) {
> +	...
> +
> +	Name (_DSD, Package() {
> +		ToUUID("XXXXX"),
> +		Package() {
> +			Package(2) {"#clock-cells", 0},
> +			Package(2) {"clock-frequency", "10000"}
> +		}
> +	})
> +
> +	...
> +}
> +
> +Device (USR1) {
> +	...
> +
> +	Name (_DSD, Package() {
> +		ToUUID("XXXXX"),
> +		Package() {
> +			Package(2) {"clocks", Package() {1, ^CLK0}}},
> +		}
> +	})
> +
> +	...
> +}

Really? This looks wrong. The above example goes right back to
conceptually putting the clock tree into ACPI. I would expect the ACPI
way to expose current clock rate to an individual device driver is to
expose a clock rate method that internally knows how to return the
currently set rate.

g.

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