linux-kernel - Re: [PATCH 7/9] ARC: use fixed frequencies in arc_set_early_base

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Date:	Tue, 2 Feb 2016 14:26:24 +0000
From:	Alexey Brodkin <Alexey.Brodkin@...opsys.com>
To:	"christian.ruppert@...tech.com" <christian.ruppert@...tech.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Vineet.Gupta1@...opsys.com" <Vineet.Gupta1@...opsys.com>,
	"noamc@...hip.com" <noamc@...hip.com>,
	"linux-snps-arc@...ts.infradead.org" 
	<linux-snps-arc@...ts.infradead.org>
Subject: Re: [PATCH 7/9] ARC: use fixed frequencies in
 arc_set_early_base_baud()

Hi Christian,

On Tue, 2016-02-02 at 14:43 +0100, christian.ruppert@...tech.com wrote:
> Alexey Brodkin <Alexey.Brodkin@...opsys.com> wrote on 02.02.2016 13:53:26:
> > 
> > Adding Christian for Abilis TB10x clocks review.
> > 
> > On Tue, 2016-02-02 at 16:28 +0530, Vineet Gupta wrote:
> > > From: Alexey Brodkin <abrodkin@...opsys.com>
> > > 
> > > UARTs usually have fixed clock so we're switching to use of
> > > constant values instead of something derived from core clock
> > > frequency.
> > > 
> > > Among other things this will allow us to get rid of
> > > arc_{get|set}_core_freq() and switch to generic clock
> > > framework later on.
> > > 
> > > Signed-off-by: Alexey Brodkin <abrodkin@...opsys.com>
> > > Signed-off-by: Vineet Gupta <vgupta@...opsys.com>
> > > ---
> > >  arch/arc/kernel/devtree.c | 6 ++----
> > >  1 file changed, 2 insertions(+), 4 deletions(-)
> > > 
> > > diff --git a/arch/arc/kernel/devtree.c b/arch/arc/kernel/devtree.c
> > > index 7e844fd8213f..e155126c79b1 100644
> > > --- a/arch/arc/kernel/devtree.c
> > > +++ b/arch/arc/kernel/devtree.c
> > > @@ -28,14 +28,12 @@ unsigned int __init arc_early_base_baud(void)
> > > 
> > >  static void __init arc_set_early_base_baud(unsigned long dt_root)
> > >  {
> > > -   unsigned int core_clk = arc_get_core_freq();
> > > -
> > >     if (of_flat_dt_is_compatible(dt_root, "abilis,arc-tb10x"))
> > > -      arc_base_baud = core_clk/3;
> > > +      arc_base_baud = 166666667;   /* Fixed 166.7MHz clk (TB10x) */
> 
> Actually, (int)core_clk/(int)3 is 166666666 not 166666667.
> I seem to remember that this rounding detail did make a difference at some 
> point. Unluckily, the details are long forgotten in the mist of time...

Interesting :)

I did that rounding intentionally hoping for the best.
But so good we've got your valuable input before it's too late.

-Alexey