linux-kernel - Re: [PATCH v3 1/3] base: power: Add generic OF-based power domain look-up

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Date:	Mon, 28 Apr 2014 11:35:31 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Tomasz Figa <t.figa@...sung.com>, linux-pm@...r.kernel.org
CC:	linux-kernel@...r.kernel.org, linux-samsung-soc@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Pavel Machek <pavel@....cz>, Len Brown <len.brown@...el.com>,
	Russell King <linux@....linux.org.uk>,
	Kukjin Kim <kgene.kim@...sung.com>,
	Kumar Gala <galak@...eaurora.org>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Mark Rutland <mark.rutland@....com>,
	Pawel Moll <pawel.moll@....com>,
	Rob Herring <robh+dt@...nel.org>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	Mark Brown <broonie@...nel.org>,
	Stephen Boyd <sboyd@...eaurora.org>,
	Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Tomasz Figa <tomasz.figa@...il.com>,
	Kevin Hilman <khilman@...aro.org>,
	Philipp Zabel <philipp.zabel@...il.com>
Subject: Re: [PATCH v3 1/3] base: power: Add generic OF-based power domain
 look-up

On 04/23/2014 10:46 AM, Tomasz Figa wrote:
> This patch introduces generic code to perform power domain look-up using
> device tree and automatically bind devices to their power domains.
> Generic device tree binding is introduced to specify power domains of
> devices in their device tree nodes.
> 
> Backwards compatibility with legacy Samsung-specific power domain
> bindings is provided, but for now the new code is not compiled when
> CONFIG_ARCH_EXYNOS is selected to avoid collision with legacy code. This
> will change as soon as Exynos power domain code gets converted to use
> the generic framework in further patch.

> diff --git a/Documentation/devicetree/bindings/power/power_domain.txt b/Documentation/devicetree/bindings/power/power_domain.txt

> +==Power domain consumers==
> +
> +Required properties:
> + - power-domain : A phandle and power domain specifier as defined by bindings
> +                  of power controller specified by phandle.

It seems quite likely that a single logical device could have components
in multiple power domains. Consider an HDMI controller with different
power domains for the HDMI core, CEC communication, DDC/I2C
communication, and the I/O pads, with no clear separation between those
two components of the module (no separate register spaces, but the
bits/registers are interleaved all together).

As such, I think that rather than a "power-domain" property, we need a
pair of "power-domains", and "power-domain-names" properties, and
preferably with mandatory usage of name-based lookups, rather than
allowing a random mix of name-based and index-based lookups like we have
with some existing resource bindings.
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