Re: [PATCH v4 2/8] Documentation: arm: define DT cpu capacity bindings

From: Juri Lelli
Date: Tue Mar 22 2016 - 05:49:19 EST

On 21/03/16 17:51, Mark Brown wrote:
> On Mon, Mar 21, 2016 at 05:24:52PM +0000, Juri Lelli wrote:
> > I think this should work, but we have to understand how do we obtain the
> > max frequency of each cluster while parsing DT. OPP bindings are
> > helpful, but AFAIK there are platforms for which firmware is responsible
> > for setting up and advertise available OPPs. I'm not sure if this
> > happens later on during the boot process. We might still be able to use
> > the clock-frequency property in this case, but that might need changing
> > again if the top OPP gets removed/changed.
> > OTH, we might simply want to say that capacity values are to be obtained
> > once the platform is "stable" (no additional changes to configuration,
> > OPPs, etc.). But this is maybe not acceptable?
> How about we just punt and let the cpufreq driver tell us - it can parse
> DT, use built in tables or whatever? We could even remember the raw
> values and recalculate if it ever decides to change for some reason.
> Until cpufreq comes up we'll be stuck at whatever OPP that we're at on
> startup which may not match whatever we define the numbers relative to
> anyway.

OK, I'll try and see how that can be done.


- Juri

> > Also, I fear that for variants of a particular implementation we will
> > still have to redo the profiling anyway (like we alreaady did for Juno
> > and Juno-r2 for example).
> This sometimes happens either through binning or through board design
> decisions rather than through new silicon so we might be able to reuse.