[7/9] ARC: use fixed frequencies in arc_set_early_base_baud()

From: Alexey Brodkin <abrodkin@synopsys.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@synopsys.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
---
 arch/arc/kernel/devtree.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

Adding Christian for Abilis TB10x clocks review.

On Tue, 2016-02-02 at 16:28 +0530, Vineet Gupta wrote:
> From: Alexey Brodkin <abrodkin@synopsys.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@synopsys.com>
> Signed-off-by: Vineet Gupta <vgupta@synopsys.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) */
>  	else if (of_flat_dt_is_compatible(dt_root, "snps,arc-sdp"))
>  		arc_base_baud = 33333333;	/* Fixed 33MHz clk (AXS10x) */
>  	else
> -		arc_base_baud = core_clk;
> +		arc_base_baud = 50000000;	/* Fixed default 50MHz */
>  }
>  #else
>  #define arc_set_early_base_baud(dt_root)

-Alexey

Alexey Brodkin <Alexey.Brodkin@synopsys.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@synopsys.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@synopsys.com>
> > Signed-off-by: Vineet Gupta <vgupta@synopsys.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...

> >     else if (of_flat_dt_is_compatible(dt_root, "snps,arc-sdp"))
> >        arc_base_baud = 33333333;   /* Fixed 33MHz clk (AXS10x) */
> >     else
> > -      arc_base_baud = core_clk;
> > +      arc_base_baud = 50000000;   /* Fixed default 50MHz */
> >  }
> >  #else
> >  #define arc_set_early_base_baud(dt_root)
> 
> -Alexey

Hi Christian,

On Tue, 2016-02-02 at 14:43 +0100, christian.ruppert@alitech.com wrote:
> Alexey Brodkin <Alexey.Brodkin@synopsys.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@synopsys.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@synopsys.com>
> > > Signed-off-by: Vineet Gupta <vgupta@synopsys.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