linux-kernel - Re: [PATCH 1/3] x86: enable common clk on x86

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Message-ID: <2235088.IlKyunT6NE@vostro.rjw.lan>
Date:	Thu, 17 Jan 2013 23:38:25 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
	Len Brown <lenb@...nel.org>,
	Mike Turquette <mturquette@...aro.org>,
	Arnd Bergmann <arnd@...db.de>,
	Linus Walleij <linus.walleij@...aro.org>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	linux-acpi@...r.kernel.org
Subject: Re: [PATCH 1/3] x86: enable common clk on x86

On Wednesday, January 16, 2013 05:28:07 PM Mika Westerberg wrote:
> On Wed, Jan 16, 2013 at 04:01:20PM +0100, Rafael J. Wysocki wrote:
> > On Wednesday, January 16, 2013 07:20:54 AM Mika Westerberg wrote:
> > > On Wed, Jan 16, 2013 at 12:59:17AM +0100, Rafael J. Wysocki wrote:
> > > > On Monday, January 14, 2013 04:46:26 PM Mika Westerberg wrote:
> > > > > We are starting to see traditional SoC peripherals also in the x86 world,
> > > > > things like UART, I2C and SPI controllers that might already have a working
> > > > > device driver. These drivers typically take advantage of the Linux clk
> > > > > framework to control and retrieve information about the peripheral clock.
> > > > > 
> > > > > There hasn't been a standard way on x86 to pass the clock rate from
> > > > > whatever configuration system is used to the driver, but instead different
> > > > > variations have emerged, like adding this information to the platform data.
> > > > > 
> > > > > In order to use the standard Linux way we enable the common clk subsystem
> > > > > also on x86. This allows us to re-use the drivers with little or no
> > > > > modification wrt. clock API usage.
> > > > > 
> > > > > This patch was originally proposed by Mark Brown.
> > > > 
> > > > Are there any side effects of selecting COMMON_CLK by an arch and if so then
> > > > what are they?
> > > 
> > > Selecting COMMON_CLK also selects HAVE_CLK, so drivers that are dependent
> > > on that option become available when you run make config.
> > 
> > Well, that's not very nice.  Do you know how many of them there are?
> 
> There are few. I tried how many I get on my config and there were 9 new
> questions with 'make oldconfig'.
> 
> Grepping (if I did it correctly) reveals:
> 
> % git grep 'depends .*HAVE_CLK' -- '*/Kconfig' | wc -l
> 27
> 
> > Distros often build all drivers available regardless of whether or not they
> > are going to be used and it would be kind of wasteful for them to build drivers
> > that aren't even going to work.
> 
> If a driver depends only on HAVE_CLK and doesn't work everywhere, there is
> a problem in that particular driver and its Kconfig options (some
> dependencies are missing). These drivers should be fixed.

Well, on a second thought it might be better to add a new Kconfig option for
x86, say CONFIG_INTEL_LPSS ("Intel LPSS Support") that will select COMMON_CLK
and depend on ACPI.  This way we'll only compile the clocks stuff when
explicitly requested (although distros will probably set that to 'y' anyway).

Thanks,
Rafael


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