Re: [PATCH v2 3/9] ARM: clps711x: Adds config option for CPU PLL multiplier

From: Sascha Hauer <s.hauer@pengutronix.de>
To: Alexander Shiyan <shc_work@mail.ru>
Cc: barebox@lists.infradead.org
Subject: Re: [PATCH v2 3/9] ARM: clps711x: Adds config option for CPU PLL multiplier
Date: Wed, 13 Feb 2013 18:40:51 +0100	[thread overview]
Message-ID: <20130213174051.GH1906@pengutronix.de> (raw)
In-Reply-To: <1360776009.524936687@f310.mail.ru>

On Wed, Feb 13, 2013 at 09:20:09PM +0400, Alexander Shiyan wrote:
> > > Signed-off-by: Alexander Shiyan <shc_work@mail.ru>
> > > ---
> > >  arch/arm/boards/clep7212/lowlevel.c            |    6 +++++-
> > >  arch/arm/mach-clps711x/Kconfig                 |   13 +++++++++++++
> > >  arch/arm/mach-clps711x/include/mach/clps711x.h |    2 +-
> > >  arch/arm/mach-clps711x/lowlevel.c              |    7 +++++--
> > >  4 files changed, 24 insertions(+), 4 deletions(-)
> > > 
> > > diff --git a/arch/arm/boards/clep7212/lowlevel.c b/arch/arm/boards/clep7212/lowlevel.c
> > > index b7d6d1d..fcf8285 100644
> > > --- a/arch/arm/boards/clep7212/lowlevel.c
> > > +++ b/arch/arm/boards/clep7212/lowlevel.c
> > > @@ -14,9 +14,13 @@
> > >  
> > >  #include <mach/clps711x.h>
> > >  
> > > +#if (CONFIG_CLPS711X_CPU_PLL_MULT < 20) || (CONFIG_CLPS711X_CPU_PLL_MULT > 50)
> > > +# error "CPU PLL multiplier out of range"
> > > +#endif
> > > +
> > >  void __naked __bare_init barebox_arm_reset_vector(void)
> > >  {
> > >  	arm_cpu_lowlevel_init();
> > >  
> > > -	clps711x_barebox_entry();
> > > +	clps711x_barebox_entry(CONFIG_CLPS711X_CPU_PLL_MULT);
> > 
> > I don't quite understand why you want to have this configurable. I mean
> > this is a single board only, why not simply run it with the maximum
> > allowed frequency? Or does this board come with multiple SoCs for which
> > different maximum values exist?
> 
> Yes. There are 2 versions of the chip. One with a maximum operating
> frequency of 74 MHz, second with 90 MHz. The only difference is on the CPU label.
> Which version is used, it is impossible to know in runtime.
> You can simply reject this patch [3/9], all other should not depend on this one.
> Later I'll try to make another different version.

Ok, thanks for explaining. It's really discouraged to put such things in
Kconfig, but in this case it seems acceptable: There's no way to detect
it during runtime *and* it varies across the same board type. So I
applied this series.

One option out of this might be that you could always startup with 74MHz
and add a command to switch to 90MHz. You could put this into the
environment on boards that you know work with 90MHz. Aynway, I don't
want to force you to do this on an Architecture you're probably
currently the only user of.

Sascha

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