Re: [Xen-devel] [PATCH 0/4] ARM: add PSCI host support

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Mon, 2013-11-25 at 13:00 +0000, George Dunlap wrote:
> On Mon, Nov 25, 2013 at 12:02 PM, Andre Przywara
> <andre.przywara@xxxxxxxxxx> wrote:
> > Xen did not make use of the host provided ARM PSCI (Power State
> > Coordination Interface) functionality so far, but relied on platform
> > specific SMP bringup functions.
> > This series adds support for PSCI on the host by reading the required
> > information from the DTB and invoking the appropriate handler when
> > bringing up each single CPU.
> > Since PSCI is defined for both ARM32 and ARM64, I put the code in a
> > file shared by both.
> > The ARM32 code was tested on Midway, but the ARM64 code was compile
> > tested only.
> >
> > This approach seems to be the least intrusive, but one could also use
> > more of the current ARM64 code by copying the PSCI/spin-table
> > distinction code to a shared file and use that from both
> > architectures. However that seems more complicated.
> >
> > Please take a look and complain ;-)
> >
> > Signed-off-by: Andre Przywara <andre.przywara@xxxxxxxxxx>
> 
> Ian, do you agree that this is too late for 4.4?

I'm in two minds. On the one hand none of the existing platforms
currently require this functionality, so it has clearly not been
necessary up to now.

On the other hand it plays into the strategy of allowing people to
trivially support their platform, and since it is a standard way to do
power control on ARM (albeit quite new and so far uptake is not huge) I
think it is expected that many new platforms will use it.

Of our current platforms Midway can optionally use PSCI (we have
"native" code at the minute) and sunxi is going to need it whenever SMP
is enabled (patches to u-boot are circulating now).

I'm inclined towards punting on this for 4.4.0 but be open to the idea
of adding it in 4.4.1 if it turns out to be something that people are
needing in practice..

An alternative could be requiring for 4.4 that the platform code
explicitly call into/request PSCI for 4.4 and only move to automatically
using it in the absence of the platform code saying otherwise for 4.5.
This has the advantage of being zero risk, but the downside of not being
very well tested (we could enable it for Midway, with the attendant
increase in risk).

Ian.


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