On Sat, 2013-03-02 at 04:48 +0800, Mike Turquette wrote:
> Quoting Mike Turquette (2013-03-01 10:22:34)
> > Quoting Bill Huang (2013-03-01 01:41:31)
> > > On Thu, 2013-02-28 at 12:49 +0800, Mike Turquette wrote:
> > > > Dynamic voltage and frequency scaling (dvfs) is a common power saving
> > > > technique in many of today's modern processors. This patch introduces a
> > > > common clk rate-change notifier handler which scales voltage
> > > > appropriately whenever clk_set_rate is called on an affected clock.
> > >
> > > I really think clk_enable and clk_disable should also be triggering
> > > notifier call and DVFS should act accordingly since there are cases
> > > drivers won't set clock rate but instead disable its clock directly, do
> > > you agree?
> > > >
> >
> > Hi Bill,
> >
> > I'll think about this. Perhaps a better solution would be to adapt
> > these drivers to runtime PM. Then a call to runtime_pm_put() would
> > result in a call to clk_disable(...) and regulator_set_voltage(...).
> >
> > There is no performance-based equivalent to runtime PM, which is one
> > reason why clk_set_rate is a likely entry point into dvfs. But for
> > operations that have nice api's like runtime PM it would be better to
> > use those interfaces and not overload the clk.h api unnecessarily.
> >
>
> Bill,
>
> I wasn't thinking at all when I wrote this. Trying to rush to the
> airport I guess...
>
> clk_enable() and clk_disable() must not sleep and all operations are
> done under a spinlock. So this rules out most use of notifiers. It is
> expected for some drivers to very aggressively enable/disable clocks in
> interrupt handlers so scaling voltage as a function of clk_{en|dis}able
> calls is also likely out of the question.
Yeah for those existing drivers to call enable/disable clocks in
interrupt have ruled out this, I didn't think through when I was asking.
>
> Some platforms have chosen to implement voltage scaling in their
> .prepare callbacks. I personally do not like this and still prefer
> drivers be adapted to runtime pm and let those callbacks handle voltage
> scaling along with clock handling.
I think different SoC have different mechanisms or constraints on doing
their DVFS, such as Tegra VDD_CORE rail, it supplies power to many
devices and as a consequence each device do not have their own power
rail to control, instead a central driver to handle/control this power
rail is needed (to set voltage at the maximum of the requested voltage
from all its sub-devices), so I'm wondering even if every drivers are
doing DVFS through runtime pm, we're still having hole on knowing
whether or not clocks of the interested devices are enabled/disabled at
runtime, I'm not familiar with runtime pm and hence do not know if there
is a mechanism to handle this, I'll study a bit. Thanks.
>
> Regards,
> Mike
>
> > > > There are three prerequisites to using this feature:
> > > >
> > > > 1) the affected clocks must be using the common clk framework
> > > > 2) voltage must be scaled using the regulator framework
> > > > 3) clock frequency and regulator voltage values must be paired via the
> > > > OPP library
> > >
> > > Just a note, Tegra Core won't meet prerequisite #3 since each regulator
> > > voltage values is associated with clocks driving those many sub-HW
> > > blocks in it.
> >
> > This patch isn't the one and only way to perform dvfs. It is just a
> > helper function for registering notifier handlers for systems that meet
> > the above three requirements. Even if you do not use the OPP library
> > there is no reason why you could not register your own rate-change
> > notifier handler to implement dvfs using whatever lookup-table you use
> > today.
> >
> > And patches are welcome to extend the usefulness of this helper. I'd
> > like as many people to benefit from this mechanism as possible.
The extension is not so easy for us though since OPP library is assuming
each device has a 1-1 mapping on its operating frequency and voltage.
> >
> > At some point we should think hard about DT bindings for these operating
> > points...
> >
> > Regards,
> > Mike
On Fri, Mar 01, 2013 at 06:55:54PM -0800, Bill Huang wrote:
> On Sat, 2013-03-02 at 04:48 +0800, Mike Turquette wrote:
> > Quoting Mike Turquette (2013-03-01 10:22:34)
> > > Quoting Bill Huang (2013-03-01 01:41:31)
> > > > On Thu, 2013-02-28 at 12:49 +0800, Mike Turquette wrote:
> > > > > Dynamic voltage and frequency scaling (dvfs) is a common power saving
> > > > > technique in many of today's modern processors. This patch introduces a
> > > > > common clk rate-change notifier handler which scales voltage
> > > > > appropriately whenever clk_set_rate is called on an affected clock.
> > > >
> > > > I really think clk_enable and clk_disable should also be triggering
> > > > notifier call and DVFS should act accordingly since there are cases
> > > > drivers won't set clock rate but instead disable its clock directly, do
> > > > you agree?
> > > > >
> > >
> > > Hi Bill,
> > >
> > > I'll think about this. Perhaps a better solution would be to adapt
> > > these drivers to runtime PM. Then a call to runtime_pm_put() would
> > > result in a call to clk_disable(...) and regulator_set_voltage(...).
> > >
> > > There is no performance-based equivalent to runtime PM, which is one
> > > reason why clk_set_rate is a likely entry point into dvfs. But for
> > > operations that have nice api's like runtime PM it would be better to
> > > use those interfaces and not overload the clk.h api unnecessarily.
> > >
> >
> > Bill,
> >
> > I wasn't thinking at all when I wrote this. Trying to rush to the
> > airport I guess...
> >
> > clk_enable() and clk_disable() must not sleep and all operations are
> > done under a spinlock. So this rules out most use of notifiers. It is
> > expected for some drivers to very aggressively enable/disable clocks in
> > interrupt handlers so scaling voltage as a function of clk_{en|dis}able
> > calls is also likely out of the question.
>
> Yeah for those existing drivers to call enable/disable clocks in
> interrupt have ruled out this, I didn't think through when I was asking.
> >
> > Some platforms have chosen to implement voltage scaling in their
> > .prepare callbacks. I personally do not like this and still prefer
> > drivers be adapted to runtime pm and let those callbacks handle voltage
> > scaling along with clock handling.
Voltage scaling in clock notifiers seems similar. Clock and regulater
embedded code into each other will cause things complicated.
>
> I think different SoC have different mechanisms or constraints on doing
> their DVFS, such as Tegra VDD_CORE rail, it supplies power to many
> devices and as a consequence each device do not have their own power
> rail to control, instead a central driver to handle/control this power
> rail is needed (to set voltage at the maximum of the requested voltage
> from all its sub-devices), so I'm wondering even if every drivers are
> doing DVFS through runtime pm, we're still having hole on knowing
> whether or not clocks of the interested devices are enabled/disabled at
> runtime, I'm not familiar with runtime pm and hence do not know if there
> is a mechanism to handle this, I'll study a bit. Thanks.
> >
> > Regards,
> > Mike
> >
> > > > > There are three prerequisites to using this feature:
> > > > >
> > > > > 1) the affected clocks must be using the common clk framework
> > > > > 2) voltage must be scaled using the regulator framework
> > > > > 3) clock frequency and regulator voltage values must be paired via the
> > > > > OPP library
> > > >
> > > > Just a note, Tegra Core won't meet prerequisite #3 since each regulator
> > > > voltage values is associated with clocks driving those many sub-HW
> > > > blocks in it.
> > >
> > > This patch isn't the one and only way to perform dvfs. It is just a
> > > helper function for registering notifier handlers for systems that meet
> > > the above three requirements. Even if you do not use the OPP library
> > > there is no reason why you could not register your own rate-change
> > > notifier handler to implement dvfs using whatever lookup-table you use
> > > today.
> > >
> > > And patches are welcome to extend the usefulness of this helper. I'd
> > > like as many people to benefit from this mechanism as possible.
>
> The extension is not so easy for us though since OPP library is assuming
> each device has a 1-1 mapping on its operating frequency and voltage.
Is there someone working on OPP clock/regulator sets support?
Thanks
Richard
> > >
> > > At some point we should think hard about DT bindings for these operating
> > > points...
> > >
> > > Regards,
> > > Mike
>
>
>
> _______________________________________________
> linux-arm-kernel mailing list
> [email protected]
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
Quoting Richard Zhao (2013-03-02 00:22:19)
> On Fri, Mar 01, 2013 at 06:55:54PM -0800, Bill Huang wrote:
> > On Sat, 2013-03-02 at 04:48 +0800, Mike Turquette wrote:
> > > Quoting Mike Turquette (2013-03-01 10:22:34)
> > > > Quoting Bill Huang (2013-03-01 01:41:31)
> > > > > On Thu, 2013-02-28 at 12:49 +0800, Mike Turquette wrote:
> > > > > > Dynamic voltage and frequency scaling (dvfs) is a common power saving
> > > > > > technique in many of today's modern processors. This patch introduces a
> > > > > > common clk rate-change notifier handler which scales voltage
> > > > > > appropriately whenever clk_set_rate is called on an affected clock.
> > > > >
> > > > > I really think clk_enable and clk_disable should also be triggering
> > > > > notifier call and DVFS should act accordingly since there are cases
> > > > > drivers won't set clock rate but instead disable its clock directly, do
> > > > > you agree?
> > > > > >
> > > >
> > > > Hi Bill,
> > > >
> > > > I'll think about this. Perhaps a better solution would be to adapt
> > > > these drivers to runtime PM. Then a call to runtime_pm_put() would
> > > > result in a call to clk_disable(...) and regulator_set_voltage(...).
> > > >
> > > > There is no performance-based equivalent to runtime PM, which is one
> > > > reason why clk_set_rate is a likely entry point into dvfs. But for
> > > > operations that have nice api's like runtime PM it would be better to
> > > > use those interfaces and not overload the clk.h api unnecessarily.
> > > >
> > >
> > > Bill,
> > >
> > > I wasn't thinking at all when I wrote this. Trying to rush to the
> > > airport I guess...
> > >
> > > clk_enable() and clk_disable() must not sleep and all operations are
> > > done under a spinlock. So this rules out most use of notifiers. It is
> > > expected for some drivers to very aggressively enable/disable clocks in
> > > interrupt handlers so scaling voltage as a function of clk_{en|dis}able
> > > calls is also likely out of the question.
> >
> > Yeah for those existing drivers to call enable/disable clocks in
> > interrupt have ruled out this, I didn't think through when I was asking.
> > >
> > > Some platforms have chosen to implement voltage scaling in their
> > > .prepare callbacks. I personally do not like this and still prefer
> > > drivers be adapted to runtime pm and let those callbacks handle voltage
> > > scaling along with clock handling.
> Voltage scaling in clock notifiers seems similar. Clock and regulater
> embedded code into each other will cause things complicated.
Hi Richard,
Sorry, I do not follow the above statement. Can you clarify what you
mean?
> >
> > I think different SoC have different mechanisms or constraints on doing
> > their DVFS, such as Tegra VDD_CORE rail, it supplies power to many
> > devices and as a consequence each device do not have their own power
> > rail to control, instead a central driver to handle/control this power
> > rail is needed (to set voltage at the maximum of the requested voltage
> > from all its sub-devices), so I'm wondering even if every drivers are
> > doing DVFS through runtime pm, we're still having hole on knowing
> > whether or not clocks of the interested devices are enabled/disabled at
> > runtime, I'm not familiar with runtime pm and hence do not know if there
> > is a mechanism to handle this, I'll study a bit. Thanks.
> > >
> > > Regards,
> > > Mike
> > >
> > > > > > There are three prerequisites to using this feature:
> > > > > >
> > > > > > 1) the affected clocks must be using the common clk framework
> > > > > > 2) voltage must be scaled using the regulator framework
> > > > > > 3) clock frequency and regulator voltage values must be paired via the
> > > > > > OPP library
> > > > >
> > > > > Just a note, Tegra Core won't meet prerequisite #3 since each regulator
> > > > > voltage values is associated with clocks driving those many sub-HW
> > > > > blocks in it.
> > > >
> > > > This patch isn't the one and only way to perform dvfs. It is just a
> > > > helper function for registering notifier handlers for systems that meet
> > > > the above three requirements. Even if you do not use the OPP library
> > > > there is no reason why you could not register your own rate-change
> > > > notifier handler to implement dvfs using whatever lookup-table you use
> > > > today.
> > > >
> > > > And patches are welcome to extend the usefulness of this helper. I'd
> > > > like as many people to benefit from this mechanism as possible.
> >
> > The extension is not so easy for us though since OPP library is assuming
> > each device has a 1-1 mapping on its operating frequency and voltage.
> Is there someone working on OPP clock/regulator sets support?
>
No, but I'm going to bring this up at LCA on Wednesday. It would be
nice to have some DT bindings for declaring operating points that tie
clocks & regulators together.
Regards,
Mike
> Thanks
> Richard
> > > >
> > > > At some point we should think hard about DT bindings for these operating
> > > > points...
> > > >
> > > > Regards,
> > > > Mike
> >
> >
> >
> > _______________________________________________
> > linux-arm-kernel mailing list
> > [email protected]
> > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
Hi Mike,
On Sun, Mar 03, 2013 at 02:54:24AM -0800, Mike Turquette wrote:
> Quoting Richard Zhao (2013-03-02 00:22:19)
> > On Fri, Mar 01, 2013 at 06:55:54PM -0800, Bill Huang wrote:
> > > On Sat, 2013-03-02 at 04:48 +0800, Mike Turquette wrote:
> > > > Quoting Mike Turquette (2013-03-01 10:22:34)
> > > > > Quoting Bill Huang (2013-03-01 01:41:31)
> > > > > > On Thu, 2013-02-28 at 12:49 +0800, Mike Turquette wrote:
> > > > > > > Dynamic voltage and frequency scaling (dvfs) is a common power saving
> > > > > > > technique in many of today's modern processors. This patch introduces a
> > > > > > > common clk rate-change notifier handler which scales voltage
> > > > > > > appropriately whenever clk_set_rate is called on an affected clock.
> > > > > >
> > > > > > I really think clk_enable and clk_disable should also be triggering
> > > > > > notifier call and DVFS should act accordingly since there are cases
> > > > > > drivers won't set clock rate but instead disable its clock directly, do
> > > > > > you agree?
> > > > > > >
> > > > >
> > > > > Hi Bill,
> > > > >
> > > > > I'll think about this. Perhaps a better solution would be to adapt
> > > > > these drivers to runtime PM. Then a call to runtime_pm_put() would
> > > > > result in a call to clk_disable(...) and regulator_set_voltage(...).
> > > > >
> > > > > There is no performance-based equivalent to runtime PM, which is one
> > > > > reason why clk_set_rate is a likely entry point into dvfs. But for
> > > > > operations that have nice api's like runtime PM it would be better to
> > > > > use those interfaces and not overload the clk.h api unnecessarily.
> > > > >
> > > >
> > > > Bill,
> > > >
> > > > I wasn't thinking at all when I wrote this. Trying to rush to the
> > > > airport I guess...
> > > >
> > > > clk_enable() and clk_disable() must not sleep and all operations are
> > > > done under a spinlock. So this rules out most use of notifiers. It is
> > > > expected for some drivers to very aggressively enable/disable clocks in
> > > > interrupt handlers so scaling voltage as a function of clk_{en|dis}able
> > > > calls is also likely out of the question.
> > >
> > > Yeah for those existing drivers to call enable/disable clocks in
> > > interrupt have ruled out this, I didn't think through when I was asking.
> > > >
> > > > Some platforms have chosen to implement voltage scaling in their
> > > > .prepare callbacks. I personally do not like this and still prefer
> > > > drivers be adapted to runtime pm and let those callbacks handle voltage
> > > > scaling along with clock handling.
> > Voltage scaling in clock notifiers seems similar. Clock and regulater
> > embedded code into each other will cause things complicated.
>
> Hi Richard,
>
> Sorry, I do not follow the above statement. Can you clarify what you
> mean?
As we have agreement that a operating point may have multiple clocks
and regulators, this patch is impossible to support multi clocks. And
it might mislead dvfs implementer to use clock notifier. It may be good
to have unified api like dvfs_set_opp(opp), or drivers can handle clocks
and regulators theirselves which is more flexible. What do you think?
Thanks
Richard