Clocks used by another OS/CPU (was: Re: [RFC PATCH] clk: renesas: cpg-mssr: Add interface for critical core clocks)

On Tue, Jul 04, 2017 at 09:49:25AM +0100, Sudeep Holla wrote:

On 04/07/17 08:31, Peter De Schrijver wrote:

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On Mon, Jul 03, 2017 at 10:17:22AM +0100, Sudeep Holla wrote:

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On 01/07/17 19:14, Uwe Kleine-K?nig wrote:

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Hello,

On Sat, Jul 01, 2017 at 07:02:48AM +0200, Dirk Behme wrote:

[...]

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The other problem is security related. If, at all, you have to do it the
other way around, then:

Make Linux a consumer of the other CPU's (trusted/trustzone/whatever
secured) OS clock driver.

Yes, that's better and is getting common on newer platforms. They have
separate M-class(or even low A-class e.g. A5/A7) processors to handle
all the system management.

The new ARM SCMI specification[0][1] is designed to standardize the
interface. It covers the clocks in clock protocol.

Yes, however this doesn't exist on older SoCs which still have multiple CPU's

Agreed. But if someone is fixing/adding support in Linux as well as in
the other OS running on those cores, why not consider this interface
instead of trying to generalize something which will invariably SoC
specific.

Because the firmware of the other CPUs might not be able to support this
or is frozen and cannot be changed.

Peter.