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

[George Dunlap <george.dunlap@eu.citrix.com>]

On 11/25/2013 02:03 PM, Ian Campbell wrote:
> 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@linaro.org> 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@linaro.org>
>> 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..

At some point every cost/benefits analysis comes down to a judgement 
call; in cases where the release coordinator doesn't have the experience 
to make the call themselves, their job should be to help set the 
criteria, ask questions, and clarify the thinking.

Both arguments -- "We should risk including this because it will enable 
other platforms, in particular sunxi", and "We should wait until 4.4.1", 
sound reasonable to me.  So I think I'll have to leave it up to you to 
judge which is a better bet at this point.  :-)

  -George