Re: [PATCH V3 4/7] cpufreq: add generic cpufreq driver

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On Wed, Dec 21, 2011 at 09:20:46AM +0800, Richard Zhao wrote:
> Hi Mark,
> 
> On Tue, Dec 20, 2011 at 11:48:45PM +0000, Mark Brown wrote:
> > On Wed, Dec 21, 2011 at 07:27:03AM +0800, Richard Zhao wrote:
> > > On Tue, Dec 20, 2011 at 02:59:04PM +0000, Mark Brown wrote:
> > 
> > > > My comments on the previous version of the patch still apply:
> > 
> > > >  - The voltage ranges being set need to be specified as ranges.
> > 
> > > cpu normally need strict voltages. and only proved operating opints
> > > are allowed to set in dts. If the voltage changes slightly especially
> > > for high frequency, it's easy to cause unstable.
> > 
> > Clearly there will be limits which get more and more restrictive as the
> > frequencies get higher but there will always be at least some play in
> > the numbers as one must at a minimum specify tolerance ranges, and at
> > lower frequencies the ranges specified will typically get compartively
> > large.
> hmm, reasonable. I'll add it in dts. Thanks.
> > 
> > Note also that not all hardware specifies things in terms of a fixed set
> > of operating points, sometimes only the minimum voltage specification is
> > varied with frequency or sometimes you see maximum and minimum stepping
> > independently.
> cpus that don't use freq table is out of scope of this driver.
> > 
> > Further note that if all hardware really does have as tight a set of
> > requirements as you suggest then the regulator support in the driver
> > needs to be non-optional otherwise a board without software regulator
> > control might drop the frequency without also dropping the voltage.
> It's ok to only adjuct freq without changes voltage. You can find many
> arm soc cpufreq drivers don't change voltage.
> If dts specify voltage but don't have such regulator. I'll assume it
> always runs on the initial volatage (highest for most cases).
> > 
> > > >  - Frequencies that can't be supported due to limitations of the
> > > >    available supplies shouldn't be exposed to users.
> > 
> > > As I said, only proved operation points are allowed.
> > 
> > This statement appears to be unrelated to the comment you're replying
> > to.
> I meant the exact voltage can always successfull set. Anyway, I'll add
> regulator_set_voltage return value checking.
> > 
> > > > You also need to define how the core supplies get looked up.
> > 
> > > It's pure software. platform uses this driver have to define "cpu" consumer.
> > 
> > You still need to define this in the binding.
> You mean regulator DT binding? already in ? I'll check it.
Mark, cpu node is not a struct device, sys_device instead. I can not find
regulator via device/dt node. Can I still use the string to get regulator
after converting to DT?

And regulator binding is not on cpufreq git tree.

Thanks
Richard
> > 
> > > > > +	pr_info("Generic CPU frequency driver\n");
> > 
> > > > This seems noisy...
> > 
> > > Why? Do you think only errors and warnings can print out?
> > 
> > Yes.
> 
> Maybe I can remove it. But I'd probably add freq table dump. It's more important.
> Agree?
> 
> I checked pr_fmt. Thanks very much. I'll use below and remove __func_.
> #define pr_fmt(fmt)             KBUILD_MODNAME ": " fmt
> 
> 
> Thanks
> Richard
> > 
> > _______________________________________________
> > linux-arm-kernel mailing list
> > linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
> > 
> 
> 
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