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

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Message-ID: <3571365.jJVUri9hzc@vostro.rjw.lan>
Date:	Thu, 10 Jan 2013 14:23:25 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc:	Mark Brown <broonie@...nsource.wolfsonmicro.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, "H. Peter Anvin" <hpa@...ux.intel.com>
Subject: Re: [PATCH 05/11] spi/pxa2xx: make clock rate configurable from platform data

On Thursday, January 10, 2013 03:07:40 PM Mika Westerberg wrote:
> On Thu, Jan 10, 2013 at 12:51:59PM +0000, Mark Brown wrote:
> > On Thu, Jan 10, 2013 at 01:54:41PM +0100, Rafael J. Wysocki wrote:
> > > On Thursday, January 10, 2013 02:38:37 PM Mika Westerberg wrote:
> > 
> > > > 	3. We make the acpi_create_platform_device() match on, lets say
> > > > 	   "INT33C" (a partial match), and in such case it assumes that we are
> > > >            running on Lynxpoint. It will then create platform device for 'clk-lpt'.
> > 
> > > > 	4. Now the clk-lpt driver creates the clocks.
> > 
> > > > 	5. The SPI driver gets the clock it wants.
> > 
> > > That sounds reasonable to me.  Mark, what do you think?
> > 
> > Sounds sensible, yes - about what I'd expect.  Is it possible to match
> > on CPUID or similar information (given that this is all in the SoC)
> > instead of ACPI, that might be more robust I guess?
> 
> I can look into that but I'm not sure whether there are any other way to
> detect are we running on Lynxpoint or not, except the device IDs (and even
> that is not 100% guaranteed because of ACPI _CIDs).

Well, we only need the clock when the SPI controller is going to be used,
so even if we have a reliable way to detect Lynxpoint, that may be not enough
(the BIOS may not expose the SPI to us, for example, in which case it will be
pointless to create the clock for it).

Thanks,
Rafael


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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