Re: [PATCH 4/4] cpufreq: arm_big_little: add SCPI interface driver

[Sudeep Holla]

On 01/05/15 15:12, Jon Medhurst (Tixy) wrote:
> On Fri, 2015-05-01 at 14:32 +0100, Sudeep Holla wrote:
> > On 01/05/15 14:19, Jon Medhurst (Tixy) wrote:
> > > On Mon, 2015-04-27 at 12:40 +0100, Sudeep Holla wrote:
> > > > On some ARM based systems, a separate Cortex-M based System Control
> > > > Processor(SCP) provides the overall power, clock, reset and system
> > > > control including CPU DVFS. SCPI Message Protocol is used to
> > > > communicate with the SCPI.
> > > >
> > > > This patch adds a interface driver for adding OPPs and registering
> > > > the arm_big_little cpufreq driver for such systems.
> > > >
> > > > Signed-off-by: Sudeep Holla <sudeep.holla@xxxxxxx>
> > > > Cc: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
> > > > Cc: "Rafael J. Wysocki" <rjw@xxxxxxxxxxxxx>
> > > > Cc: linux-pm@xxxxxxxxxxxxxxx
> > > > ---
> > > >    drivers/cpufreq/Kconfig.arm    |   9 ++++
> > > >    drivers/cpufreq/Makefile       |   1 +
> > > >    drivers/cpufreq/scpi-cpufreq.c | 103 +++++++++++++++++++++++++++++++++++++++++
> > > >    3 files changed, 113 insertions(+)
> > > >    create mode 100644 drivers/cpufreq/scpi-cpufreq.c
> > > >
> > > > diff --git a/drivers/cpufreq/Kconfig.arm b/drivers/cpufreq/Kconfig.arm
> > > > index 4f3dbc8cf729..9e678bf1687c 100644
> > > > --- a/drivers/cpufreq/Kconfig.arm
> > > > +++ b/drivers/cpufreq/Kconfig.arm
> > > > @@ -24,6 +24,15 @@ config ARM_VEXPRESS_SPC_CPUFREQ
> > > >              This add the CPUfreq driver support for Versatile Express
> > > >    	  big.LITTLE platforms using SPC for power management.
> > > >
> > > > +config ARM_SCPI_CPUFREQ
> > > > +        tristate "SCPI based CPUfreq driver"
> > > > +	depends on ARM_BIG_LITTLE_CPUFREQ && ARM_SCPI_PROTOCOL
> > >
> > > And ARM_BIG_LITTLE_CPUFREQ depends on CONFIG_ARM, so we can't build this
> > > for arm64, which is the only platform (Juno) we have to run these
> > > patches on.
> >
> > Yes I know
> >
> > > Unless you're prepared for a horrid hack...
> > > https://github.com/ARM-software/linux/commit/b9ceaa0cbd7c57d57ee7e69146cc627697570f6e
> >
> > I need to check if it can be improved before I post on the list and
> > hence dropped it in the first version of this patch-set.
> >
> > > or a pair of less horrid ones...
> > > http://git.linaro.org/kernel/linux-linaro-tracking.git/commit/4b5dd8ff98613b7e90c8f3214522a00ab6900fe9
> >
> > No not this one, this was already discussed long back I believe.
> > It doesn't make sense to add bl-switcher for ARM64 IMO.
> >
> > > http://git.linaro.org/kernel/linux-linaro-tracking.git/commit/8641dbfe253f6a9061742ca11f769fc1d82c2aaa
> >
> > Yes the Kconfig changes looks better than what I have now.
> >
> > > Any reason why the above two aren't suitable for mainline Linux? The
> > > second was actually committed then reverted because it broke arm64
> > > builds, but the other patch fixes that.
> > Yes IMO since arm-big-little also supports multi-cluster cpufreq(yes I
> > know it can be merged into cpufreq-dt once we have OPPv2 bindings, but
> > until then), it should handle the config where CONFIG_BL_SWITCHER=n and
> > that's what I have attempted in my patch above.
>
> OK, that all makes sense, just wanted to make sure things didn't get
> overlooked, because having code that has no users in mainline seemed a
> bit odd.

No issues, it's better to have remainders like this :). I plan to post
something in the next version.

Regards,
Sudeep
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