linux-kernel - Re: [PATCH v7 1/3] Documentation: common clk API

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Date:	Sat, 17 Mar 2012 21:29:31 +0100
From:	Sascha Hauer <s.hauer@...gutronix.de>
To:	"Turquette, Mike" <mturquette@...com>
Cc:	Arnd Bergmann <arnd@...db.de>, Paul Walmsley <paul@...an.com>,
	linux-arm-kernel@...ts.infradead.org,
	Amit Kucheria <amit.kucheria@...aro.org>,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	linaro-dev@...ts.linaro.org,
	Linus Walleij <linus.walleij@...aro.org>,
	Grant Likely <grant.likely@...retlab.ca>,
	Saravana Kannan <skannan@...eaurora.org>,
	Jeremy Kerr <jeremy.kerr@...onical.com>,
	Magnus Damm <magnus.damm@...il.com>,
	Deepak Saxena <dsaxena@...aro.org>, patches@...aro.org,
	Rob Herring <rob.herring@...xeda.com>,
	Russell King <linux@....linux.org.uk>,
	Thomas Gleixner <tglx@...utronix.de>,
	Richard Zhao <richard.zhao@...aro.org>,
	Shawn Guo <shawn.guo@...escale.com>,
	Linus Walleij <linus.walleij@...ricsson.com>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Stephen Boyd <sboyd@...eaurora.org>,
	linux-omap@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 1/3] Documentation: common clk API

On Sat, Mar 17, 2012 at 11:02:11AM -0700, Turquette, Mike wrote:
> On Sat, Mar 17, 2012 at 2:05 AM, Arnd Bergmann <arnd@...db.de> wrote:
> > On Friday 16 March 2012, Turquette, Mike wrote:
> >> On Fri, Mar 16, 2012 at 3:21 PM, Paul Walmsley <paul@...an.com> wrote:
> >> > From: Paul Walmsley <paul@...an.com>
> >> > Date: Fri, 16 Mar 2012 16:06:30 -0600
> >> > Subject: [PATCH] clk: mark the common clk code as EXPERIMENTAL for now
> >> >
> >> > Mark the common clk code as depending on CONFIG_EXPERIMENTAL.  The API
> >> > is not well-defined and both it and the underlying mechanics are likely
> >> > to need significant changes to support non-trivial uses of the rate
> >> > changing code, such as DVFS with external I/O devices.  So any platforms
> >> > that switch their implementation over to this may need to revise much
> >> > of their driver code and revalidate their implementations until the
> >> > behavior of the code is better-defined.
> >> >
> >> > A good time for removing this EXPERIMENTAL designation would be after at
> >> > least two platforms that do DVFS on groups of external I/O devices have
> >> > ported their clock implementations over to the common clk code.
> >> >
> >> > Signed-off-by: Paul Walmsley <paul@...an.com>
> >> > Cc: Mike Turquette <mturquette@...com>
> >>
> >> ACK.  This will set some reasonable expectations while things are in flux.
> >>
> >> Arnd are you willing to take this in?
> >
> > I think it's rather pointless, because the option is not going to
> > be user selectable but will get selected by the platform unless I'm
> > mistaken. The platform maintainers that care already know the state
> > of the framework. Also, there are no user space interfaces that we
> > have to warn users about not being stable, because the framework
> > is internal to the kernel.
> 
> The consensus seems to be to not set experimental.
> 
> > However, I wonder whether we need the patch below to prevent
> > users from accidentally enabling COMMON_CLK on platforms that
> > already provide their own implementation.
> >
> >        Arnd
> >
> > diff --git a/drivers/clk/Kconfig b/drivers/clk/Kconfig
> > index 2eaf17e..a0a83de 100644
> > --- a/drivers/clk/Kconfig
> > +++ b/drivers/clk/Kconfig
> > @@ -12,7 +12,7 @@ config HAVE_MACH_CLKDEV
> >
> >  menuconfig COMMON_CLK
> > -       bool "Common Clock Framework"
> > +       bool
> >        select HAVE_CLK_PREPARE
> >        ---help---
> >          The common clock framework is a single definition of struct
> >          clk, useful across many platforms, as well as an
> 
> Much like experimental I'm not sure how needed this change is.  The
> help section does say to leave it disabled by default, if unsure.  If
> you merge it I won't object but this might be fixing an imaginary
> problem.

Architectures without common clock support won't build with this option
enabled (multiple definition of clk_enable etc), so I think this should
not be user visible.

Sascha

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