Message-ID: <50EC90C3.2090604@intel.com>
Date:	Tue, 08 Jan 2013 22:33:55 +0100
From:	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
To:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
CC:	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	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" <rjw@...k.pl>,
	"H. Peter Anvin" <hpa@...ux.intel.com>
Subject: Re: [PATCH 05/11] spi/pxa2xx: make clock rate configurable from platform
 data

On 1/8/2013 2:10 PM, Mark Brown wrote:
> 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.

Why so?  x86 doesn't have a notion of direct clock control, at least not 
on the ACPI systems.

>>> 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...

No, it isn't.  Any suggestions?

>> 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

We're not talking about smartphones and even not about SoCs here, sorry.

This is a laptop CPU that happens to have an SPI controller integrated.

> 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.

I'm not sure what you're referring to, but here we have ACPI as a 
configuration mechanism.

Which doesn't allow us to control clocks directly.

Thanks,
Rafael

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