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

From: Sudeep Holla
Date: Fri May 01 2015 - 10:15:17 EST




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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