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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