[GIT PULL] ARM64: juno: SCPI and dependent drivers for v4.3

[GIT PULL] ARM64: juno: SCPI and dependent drivers for v4.3

[Sudeep Holla]

Hi Olof,


Here is the first pull request for SCPI, clock and cpufreq support on
ARM64 Juno development platform for v4.3

Regards,
Sudeep

The following changes since commit d770e558e21961ad6cfdf0ff7df0eb5d7d4f0754:

    Linux 4.2-rc1 (2015-07-05 11:01:52 -0700)

are available in the git repository at:

    git://linux-arm.org/linux-skn.git juno_dvfs

for you to fetch changes up to a42b1bbf7bf9a2a1fa4b0deff66581b83541b819:

    arm64: dts: add clock support for all the cpus (2015-08-05 11:03:09 
+0100)

----------------------------------------------------------------
Sudeep Holla (8):
        Documentation: add DT binding for ARM System Control and Power 
Interface(SCPI) protocol
        firmware: add support for ARM System Control and Power 
Interface(SCPI) protocol
        clk: add support for clocks provided by SCP(System Control 
Processor)
        clk: scpi: add support for cpufreq virtual device
        cpufreq: arm_big_little: add SCPI interface driver
        arm64: dts: add SRAM, MHU mailbox and SCPI support on Juno
        arm64: dts: add CPU topology on Juno
        arm64: dts: add clock support for all the cpus

   Documentation/devicetree/bindings/arm/arm,scpi.txt | 150 +++
   MAINTAINERS                                        |  10 +
   arch/arm64/boot/dts/arm/juno-base.dtsi             |  54 ++
   arch/arm64/boot/dts/arm/juno-r1.dts                |  32 +
   arch/arm64/boot/dts/arm/juno.dts                   |  32 +
   drivers/clk/Kconfig                                |  10 +
   drivers/clk/Makefile                               |   1 +
   drivers/clk/clk-scpi.c                             | 325 +++++++
   drivers/cpufreq/Kconfig.arm                        |   9 +
   drivers/cpufreq/Makefile                           |   1 +
   drivers/cpufreq/scpi-cpufreq.c                     | 124 +++
   drivers/firmware/Kconfig                           |  19 +
   drivers/firmware/Makefile                          |   1 +
   drivers/firmware/arm_scpi.c                        | 711 +++++++++++++
   include/linux/scpi_protocol.h                      |  61 ++
   15 files changed, 1540 insertions(+)
   create mode 100644 Documentation/devicetree/bindings/arm/arm,scpi.txt
   create mode 100644 drivers/clk/clk-scpi.c
   create mode 100644 drivers/cpufreq/scpi-cpufreq.c
   create mode 100644 drivers/firmware/arm_scpi.c
   create mode 100644 include/linux/scpi_protocol.h

[GIT PULL] ARM64: juno: SCPI and dependent drivers for v4.3

[Olof Johansson]

On Wed, Aug 05, 2015 at 11:22:51AM +0100, Sudeep Holla wrote:
> Hi Olof,
> 
> 
> Here is the first pull request for SCPI, clock and cpufreq support on
> ARM64 Juno development platform for v4.3

Hi,

I'd like to hear from Catalin and Will on why ARM is doing this. Catalin
and Will are pushing back very hard at vendors who don't use PSCI for
CPU power management, and then they have coworkers that are looking to
merge this directly into the kernel.

Hmm?


-Olof

[GIT PULL] ARM64: juno: SCPI and dependent drivers for v4.3

[Catalin Marinas]

On Thu, Aug 13, 2015 at 02:40:26PM +0200, Olof Johansson wrote:
> On Wed, Aug 05, 2015 at 11:22:51AM +0100, Sudeep Holla wrote:
> > Here is the first pull request for SCPI, clock and cpufreq support on
> > ARM64 Juno development platform for v4.3
> 
> I'd like to hear from Catalin and Will on why ARM is doing this. Catalin
> and Will are pushing back very hard at vendors who don't use PSCI for
> CPU power management, and then they have coworkers that are looking to
> merge this directly into the kernel.

Actually, the arm64 CPU power management story is pretty much handled by
Lorenzo and Sudeep in my team, so I trust their judgement ;). But I
agree with you that a better explanation on the reasons behind this is
needed, otherwise we risk confusing messages. I'll try to summarise it
below but Sudeep can reply with more details.

PSCI only covers CPU boot/cpuidle and platform suspend. It does not have
any provisions for DVFS and I'm not sure this could be easily
standardised (or whether we could find enough supporters to get it
adopted).

SCPI is a (standard) interface to a coprocessor handling clocks etc. to
be used with cpufreq. This patchset adds support for cpufreq/dvs which
is not handled by PSCI. So, just to clarify the acronyms:

SCPI - System Control and Power Interface - it's a protocol for
communicating with a System Control Processor (e.g. Cortex-M3) via
mailboxes. It is used in Linux for DVFS but this is *not* a secure/EL3
firmware interface (a.k.a. SMC calls). It indeed a firmware interface
but the firmware runs on a separate coprocessor and not on the CPU itself.

PSCI - Power State Coordination Interface - it is a secure firmware
interface for coordinating the CPU power states (idle, not DVFS). The
firmware may use an SCPI communication channel (e.g. deeper sleep states
where clock changes are needed).

-- 
Catalin

[GIT PULL] ARM64: juno: SCPI and dependent drivers for v4.3

[Sudeep Holla]

On 13/08/15 15:24, Catalin Marinas wrote:
> On Thu, Aug 13, 2015 at 02:40:26PM +0200, Olof Johansson wrote:
>> On Wed, Aug 05, 2015 at 11:22:51AM +0100, Sudeep Holla wrote:
>>> Here is the first pull request for SCPI, clock and cpufreq support on
>>> ARM64 Juno development platform for v4.3
>>
>> I'd like to hear from Catalin and Will on why ARM is doing this. Catalin
>> and Will are pushing back very hard at vendors who don't use PSCI for
>> CPU power management, and then they have coworkers that are looking to
>> merge this directly into the kernel.
>
> Actually, the arm64 CPU power management story is pretty much handled by
> Lorenzo and Sudeep in my team, so I trust their judgement ;). But I
> agree with you that a better explanation on the reasons behind this is
> needed, otherwise we risk confusing messages. I'll try to summarise it
> below but Sudeep can reply with more details.
>

(I will use the acronomys directly as Catalin has already explained the
difference)

Thanks Catalin for the detailed explanation. I agree that this pull
request has not much details, but the patch series makes reference only
to the clocks and features provided by the SCP(System Control Processor)
to be used by Linux(non-secure) and nothing about CPU power states that
are handled by PSCI. This SCPI is completely independent and orthogonal
to PSCI.

> PSCI only covers CPU boot/cpuidle and platform suspend. It does not have
> any provisions for DVFS and I'm not sure this could be easily
> standardised (or whether we could find enough supporters to get it
> adopted).
>

Though we are not campaigning it as aggressively as PSCI.

> SCPI is a (standard) interface to a coprocessor handling clocks etc. to
> be used with cpufreq. This patchset adds support for cpufreq/dvs which
> is not handled by PSCI. So, just to clarify the acronyms:
>
> SCPI - System Control and Power Interface - it's a protocol for
> communicating with a System Control Processor (e.g. Cortex-M3) via
> mailboxes. It is used in Linux for DVFS but this is *not* a secure/EL3
> firmware interface (a.k.a. SMC calls). It indeed a firmware interface
> but the firmware runs on a separate coprocessor and not on the CPU itself.
>
> PSCI - Power State Coordination Interface - it is a secure firmware
> interface for coordinating the CPU power states (idle, not DVFS). The
> firmware may use an SCPI communication channel (e.g. deeper sleep states
> where clock changes are needed).
>

I will add some more information to (hopefully) clarify the doubts.

SCP(System Control Processor) offers control and management of the
core/cluster power states, various power domain DVFS including the
core/cluster, certain system clocks configuration, thermal sensors and
many others.

Though the core/cluster power states are also handled this SCP,
they are accessible only through secure channels and PSCI firmware
implementations on the platform rely on that internally. Non-secure
access/requests are not possible.

Just to summarize, this SCP helps to offload all the power management
work to a dedicated low power processor which can be always running.
On Juno, its Cortex-M while on AMD Seattle it's Cortex-A5.

Regards,
Sudeep

[GIT PULL] ARM64: juno: SCPI and dependent drivers for v4.3

[Olof Johansson]

Hi,

On Thu, Aug 13, 2015 at 03:53:04PM +0100, Sudeep Holla wrote:
> 
> 
> On 13/08/15 15:24, Catalin Marinas wrote:
> >On Thu, Aug 13, 2015 at 02:40:26PM +0200, Olof Johansson wrote:
> >>On Wed, Aug 05, 2015 at 11:22:51AM +0100, Sudeep Holla wrote:
> >>>Here is the first pull request for SCPI, clock and cpufreq support on
> >>>ARM64 Juno development platform for v4.3
> >>
> >>I'd like to hear from Catalin and Will on why ARM is doing this. Catalin
> >>and Will are pushing back very hard at vendors who don't use PSCI for
> >>CPU power management, and then they have coworkers that are looking to
> >>merge this directly into the kernel.
> >
> >Actually, the arm64 CPU power management story is pretty much handled by
> >Lorenzo and Sudeep in my team, so I trust their judgement ;). But I
> >agree with you that a better explanation on the reasons behind this is
> >needed, otherwise we risk confusing messages. I'll try to summarise it
> >below but Sudeep can reply with more details.
> >
> 
> (I will use the acronomys directly as Catalin has already explained the
> difference)
> 
> Thanks Catalin for the detailed explanation. I agree that this pull
> request has not much details, but the patch series makes reference only
> to the clocks and features provided by the SCP(System Control Processor)
> to be used by Linux(non-secure) and nothing about CPU power states that
> are handled by PSCI. This SCPI is completely independent and orthogonal
> to PSCI.

Yes, I am aware that PSCI and SCPI are two confusingly similar acronyms that
represent separate things. My concern though is that we're letting in a poorly
architected solution into the kernel with SCPI. PSCI is already choosing to
abstract this outside of the kernel. Is there a reason SCPI isn't using the
same approach?

> >PSCI only covers CPU boot/cpuidle and platform suspend. It does not have
> >any provisions for DVFS and I'm not sure this could be easily
> >standardised (or whether we could find enough supporters to get it
> >adopted).
> >
> 
> Though we are not campaigning it as aggressively as PSCI.

Which, given the resistance to pick up PSCI, this is unlikely to be used by
anyone...

> >SCPI is a (standard) interface to a coprocessor handling clocks etc. to
> >be used with cpufreq. This patchset adds support for cpufreq/dvs which
> >is not handled by PSCI. So, just to clarify the acronyms:
> >
> >SCPI - System Control and Power Interface - it's a protocol for
> >communicating with a System Control Processor (e.g. Cortex-M3) via
> >mailboxes. It is used in Linux for DVFS but this is *not* a secure/EL3
> >firmware interface (a.k.a. SMC calls). It indeed a firmware interface
> >but the firmware runs on a separate coprocessor and not on the CPU itself.
> >
> >PSCI - Power State Coordination Interface - it is a secure firmware
> >interface for coordinating the CPU power states (idle, not DVFS). The
> >firmware may use an SCPI communication channel (e.g. deeper sleep states
> >where clock changes are needed).
> >
> 
> I will add some more information to (hopefully) clarify the doubts.
> 
> SCP(System Control Processor) offers control and management of the
> core/cluster power states, various power domain DVFS including the
> core/cluster, certain system clocks configuration, thermal sensors and
> many others.
> 
> Though the core/cluster power states are also handled this SCP,
> they are accessible only through secure channels and PSCI firmware
> implementations on the platform rely on that internally. Non-secure
> access/requests are not possible.
> 
> Just to summarize, this SCP helps to offload all the power management
> work to a dedicated low power processor which can be always running.
> On Juno, its Cortex-M while on AMD Seattle it's Cortex-A5.

I understand what the SCP is used for. What I don't understand is why you're
adding all this complexity in the kernel for it.

Also, is there only one known implementation of this today on Juno? Are there
others coming soon? Single-user frameworks tend to be hard to get right, and
it's usually much better to wait until it's clear it will fit more than just
the original target.

Anyway, the git server you provided the link to in the original email
(linux-arm.org) seems to be offline so I couldn't fetch a fresh copy of
the branch to look at.

It's pretty clear this is not 4.3 material at this point, so I'll take
a look at it later.


-Olof

[GIT PULL] ARM64: juno: SCPI and dependent drivers for v4.3

[Sudeep Holla]

Hi Olof,

On Fri, Aug 21, 2015 at 5:17 PM, Olof Johansson <olof@lixom.net> wrote:
> Hi,
>
> On Thu, Aug 13, 2015 at 03:53:04PM +0100, Sudeep Holla wrote:
>>
>>
>> On 13/08/15 15:24, Catalin Marinas wrote:
>> >On Thu, Aug 13, 2015 at 02:40:26PM +0200, Olof Johansson wrote:
>> >>On Wed, Aug 05, 2015 at 11:22:51AM +0100, Sudeep Holla wrote:
>> >>>Here is the first pull request for SCPI, clock and cpufreq support on
>> >>>ARM64 Juno development platform for v4.3
>> >>
>> >>I'd like to hear from Catalin and Will on why ARM is doing this. Catalin
>> >>and Will are pushing back very hard at vendors who don't use PSCI for
>> >>CPU power management, and then they have coworkers that are looking to
>> >>merge this directly into the kernel.
>> >
>> >Actually, the arm64 CPU power management story is pretty much handled by
>> >Lorenzo and Sudeep in my team, so I trust their judgement ;). But I
>> >agree with you that a better explanation on the reasons behind this is
>> >needed, otherwise we risk confusing messages. I'll try to summarise it
>> >below but Sudeep can reply with more details.
>> >
>>
>> (I will use the acronomys directly as Catalin has already explained the
>> difference)
>>
>> Thanks Catalin for the detailed explanation. I agree that this pull
>> request has not much details, but the patch series makes reference only
>> to the clocks and features provided by the SCP(System Control Processor)
>> to be used by Linux(non-secure) and nothing about CPU power states that
>> are handled by PSCI. This SCPI is completely independent and orthogonal
>> to PSCI.
>
> Yes, I am aware that PSCI and SCPI are two confusingly similar acronyms that
> represent separate things. My concern though is that we're letting in a poorly
> architected solution into the kernel with SCPI. PSCI is already choosing to
> abstract this outside of the kernel. Is there a reason SCPI isn't using the
> same approach?
>

I am not sure we can compare the CPU power states with the CPU DVFS.
In case of power states, we need to ensure all the exception levels have
saved the context and hence PSCI abstraction makes sense for the kernel.
However the CPU DVFS is mostly driven by the kernel based on the load,
so we talk directly to the power controller from the kernel.

In way SCPI is abstracting by hiding all the regulators and PLLs you need
to handle. So I may be missing to understand when you say SCPI also use
PSCI approach.

>> >PSCI only covers CPU boot/cpuidle and platform suspend. It does not have
>> >any provisions for DVFS and I'm not sure this could be easily
>> >standardised (or whether we could find enough supporters to get it
>> >adopted).
>> >
>>
>> Though we are not campaigning it as aggressively as PSCI.
>
> Which, given the resistance to pick up PSCI, this is unlikely to be used by
> anyone...
>

Agreed even I am not sure how widely will that be accepted, but we need to
support the systems which have SCPI right ? Like Juno for now.

>> >SCPI is a (standard) interface to a coprocessor handling clocks etc. to
>> >be used with cpufreq. This patchset adds support for cpufreq/dvs which
>> >is not handled by PSCI. So, just to clarify the acronyms:
>> >
>> >SCPI - System Control and Power Interface - it's a protocol for
>> >communicating with a System Control Processor (e.g. Cortex-M3) via
>> >mailboxes. It is used in Linux for DVFS but this is *not* a secure/EL3
>> >firmware interface (a.k.a. SMC calls). It indeed a firmware interface
>> >but the firmware runs on a separate coprocessor and not on the CPU itself.
>> >
>> >PSCI - Power State Coordination Interface - it is a secure firmware
>> >interface for coordinating the CPU power states (idle, not DVFS). The
>> >firmware may use an SCPI communication channel (e.g. deeper sleep states
>> >where clock changes are needed).
>> >
>>
>> I will add some more information to (hopefully) clarify the doubts.
>>
>> SCP(System Control Processor) offers control and management of the
>> core/cluster power states, various power domain DVFS including the
>> core/cluster, certain system clocks configuration, thermal sensors and
>> many others.
>>
>> Though the core/cluster power states are also handled this SCP,
>> they are accessible only through secure channels and PSCI firmware
>> implementations on the platform rely on that internally. Non-secure
>> access/requests are not possible.
>>
>> Just to summarize, this SCP helps to offload all the power management
>> work to a dedicated low power processor which can be always running.
>> On Juno, its Cortex-M while on AMD Seattle it's Cortex-A5.
>
> I understand what the SCP is used for. What I don't understand is why you're
> adding all this complexity in the kernel for it.
>

I am not sure how we can avoid that though. Any thoughts ?

> Also, is there only one known implementation of this today on Juno? Are there
> others coming soon? Single-user frameworks tend to be hard to get right, and
> it's usually much better to wait until it's clear it will fit more than just
> the original target.
>

No argument on that, the specification is not reviewed as much as PSCI but we do
have version, so can be fixed/enhanced in future. It's no different
w.r.t PSCI in that
respect IMO.

Yes currently only on Juno, but future ARM Ltd. platforms have plans to reuse
the same.

> Anyway, the git server you provided the link to in the original email
> (linux-arm.org) seems to be offline so I couldn't fetch a fresh copy of
> the branch to look at.
>

Extremely sorry for that(not much under my control :(), I will get it
fixed ASAP.
I am current away attending LPC.

> It's pretty clear this is not 4.3 material at this point, so I'll take
> a look at it later.
>

Fair enough, I understand that its too late for v4.3

Regards,
Sudeep

[GIT PULL] ARM64: juno: SCPI and dependent drivers for v4.3

[Heiko Stuebner]

Hi,

Am Freitag, 21. August 2015, 09:17:32 schrieb Olof Johansson:
> > >PSCI only covers CPU boot/cpuidle and platform suspend. It does not have
> > >any provisions for DVFS and I'm not sure this could be easily
> > >standardised (or whether we could find enough supporters to get it
> > >adopted).
> > 
> > Though we are not campaigning it as aggressively as PSCI.
> 
> Which, given the resistance to pick up PSCI, this is unlikely to be used by
> anyone...

Rockchip seems to use SCPI to offload ddr frequency to a mcu scaling on the 
rk3368 ;-)


Heiko

[GIT PULL] ARM64: juno: SCPI and dependent drivers for v4.3

[Sudeep Holla]

On 25/08/15 22:47, Heiko Stuebner wrote:
> Hi,
>
> Am Freitag, 21. August 2015, 09:17:32 schrieb Olof Johansson:
>>>> PSCI only covers CPU boot/cpuidle and platform suspend. It does not have
>>>> any provisions for DVFS and I'm not sure this could be easily
>>>> standardised (or whether we could find enough supporters to get it
>>>> adopted).
>>>
>>> Though we are not campaigning it as aggressively as PSCI.
>>
>> Which, given the resistance to pick up PSCI, this is unlikely to be used by
>> anyone...
>
> Rockchip seems to use SCPI to offload ddr frequency to a mcu scaling on the
> rk3368 ;-)
>

Good to hear that, thanks Heiko for letting us know. IMHO I must admit I
am still sceptical about large SCPI adoption.

Regards,
Sudeep