Re: [PATCH RFC v2 2/2] Documentation: arm: define DT C-states bindings

[Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>]

On Sat, Jan 25, 2014 at 08:15:46AM +0000, Antti P Miettinen wrote:
> From: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
> Subject: [PATCH RFC v2 2/2] Documentation: arm: define DT C-states bindings
> Date: Mon, 20 Jan 2014 17:47:59 +0000
> > +	- latency
> > +		Usage: Required
> > +		Value type: <prop-encoded-array>
> > +		Definition: List of u32 values representing worst case latency
> > +			    in microseconds required to enter and exit the
> > +			    C-state, one value per OPP [2]. The list should
> > +			    be specified in the same order as the operating
> > +			    points property list of the cpu this state is
> > +			    valid on.
> > +			    If no OPP bindings are present, the latency value
> > +			    is associated with the current OPP of CPUs in the
> > +			    system.
> 
> I'm afraid the CPU OPP is not enough to capture the variance in
> latencies. Especially memory frequency affects some of the latencies
> very stronly.

That's why I defined the worst case. How did you implemented it in your
idle drivers ? That would help generalize it, after all these bindings
are there to simplify drivers upstreaming, feedback welcome.

Thanks,
Lorenzo