Re: [PATCH 3/4] MIPS: cpu-probe: Set the write-combine CCA value on per core basis

[Markos Chandras <markos.chandras@imgtec.com>]

Hi Florian,

On Mon, Aug 04, 2014 at 03:54:49PM -0700, Florian Fainelli wrote:
> Hi Markos,
> 
> On 07/18/2014 02:51 AM, Markos Chandras wrote:
> > Different cores use different CCA values to achieve write-combine
> > memory writes. For cores that do not support write-combine we
> > set the default value to CCA:2 (uncached, non-coherent) which is the
> > default value as set by the kernel.
> > 
> > Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
> > ---
> [snip]
> 			break;
> > @@ -765,67 +767,83 @@ static inline void cpu_probe_legacy(struct cpuinfo_mips *c, unsigned int cpu)
> >  
> >  static inline void cpu_probe_mips(struct cpuinfo_mips *c, unsigned int cpu)
> >  {
> > +	c->writecombine = _CACHE_UNCACHED_ACCELERATED;
> 
> Why do we set this writecombine setting by default, when later we are
> going to override writecombine on a per-cpu basic.
> 
> In the end, we have the following:
> 
> cpu_probe()
> 	c->writecombine = _CACHE_UNCACHED;
> 
> 	cpu_probe_mips()
> 		c->writecombine = _CACHE_UNCACHED_ACCELERATED:
> 		... per-cpu case ...
> 		c->writecombine = _CACHE_UNCACHED;
> 
> Can't we just eliminate the various assignments in cpu_probe_mips() and
> only override c->writecombine if _CACHE_UNCACHED is not suitable?
> 
The reason I did it like this, is that new cores (eg *Aptiv family) will use
_CACHE_UNCACHED_ACCELERATED and that's why it's the 'default' option for
the MIPS cores. _CACHE_UNCACHED is only suitable for old cores.
The way it is right now, allows us to not have to set this option whenever we
add support for a new core since it will inherit the default option.

-- 
markos