linux-kernel - Re: [PATCH 05/11] spi/pxa2xx: make clock rate configurable from platform data

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Message-ID: <20130108131008.GW4544@opensource.wolfsonmicro.com>
Date:	Tue, 8 Jan 2013 13:10:08 +0000
From:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
To:	Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc:	linux-kernel@...r.kernel.org, grant.likely@...retlab.ca,
	linus.walleij@...aro.org, eric.y.miao@...il.com,
	linux@....linux.org.uk, haojian.zhuang@...il.com,
	chao.bi@...el.com, "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
Subject: Re: [PATCH 05/11] spi/pxa2xx: make clock rate configurable from
 platform data

On Tue, Jan 08, 2013 at 02:41:53PM +0200, Mika Westerberg wrote:
> On Tue, Jan 08, 2013 at 11:02:28AM +0000, Mark Brown wrote:

> > No, the way to do this is to fix x86 to enable the clock API there.  The
> > x86 maintainers couldn't be bothered when I submitted a patch and
> > getting anyone to take a patch to make it available by default appears
> > to be unreasonably hard but perhaps if someone from Intel tries the x86
> > maintainers might take a patch...

> Do you mean enabling CONFIG_COMMON_CLK on x86?

Yes.

> > We shouldn't be adding special case code to every driver that might need
> > a clock that gets used on an Intel system.

> I agree and it is cleaner to have the same API for all arches. However, I'm
> not sure how do we create the fixed clocks then? There is nothing in ACPI
> namespace (or in the ACPI 5.0 spec) that allows you to describe clocks and
> their relationships.

I'm sure it's not beyond the bounds of possibility that we could solve
this problem...

> So then we end up either:

> 	1. Creating a custom board file for Lynxpoint which creates the
> 	   clocks. This is something I think x86 maintainers don't want to
> 	   see.

> 	2. Creating the clock in the driver itself in its ACPI enumeration
> 	   implementation. This might work but it litters the drivers with
> 	   clock details.

> Or is there something I'm missing?

Well, it seems fairly clear to me that the SoC wiring ought to be done
outside the driver.

It is something that needs to be resolved for your smartphone SoCs for
this and for other things like platform data for external chips, what's
actually happening in practical systems here is that people are just
hacking the arch code as there's no mechanism for providing
configuration at present.

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