Re: [PSCI DISCUSS] How to implement standby and suspend-to-ram by PSCI

[Sudeep Holla <sudeep.holla@arm.com>]

Hi Hongbo,

On 06/05/16 11:11, Hongbo Zhang wrote:
> Hi Guys,
> We know in the legacy kernel suspend codes, a typical suspend_ops->enter
> callback is like this:
>

[...]

>
> That means we implement standby and suspend-to-ram in one callback, and
> these two state can be identified by an input parameter 'state'.
>
> While now PSCI is used for ARM to implement cores operations and power
> management, for the above suspend_ops->enter we choose SYSTEM_SUSPEND
> function, and this function is defined for suspend-to-ram, then here
> comes the problem:
>
> How can we implement the standby state following the PSCI framework?
>

Jisheng Zhang raised similar question few months back and we had a
discussion. Please have a look at the thread [1]

> I couldn't find other PSCI function which fits for standby well.
> In the spec there isn't such a 'state' parameter passed for
> SYSTEM_SUSPEND (only entry_point_address and context_id), can we change
> the spec a bit, e.g. using one more register to pass another 'state'
> parameter? is that acceptable? (similar like CPU_SUSPEND then)
>

Since the standby state is not well defined on ARM systems, it's hard to
define the conditions like system suspend and hence difficult to
generalize in the spec. I think suspend-to-idle should suffice in your
case. Anyways its better to get more information on the definition of
standby on your platform.

-- 
Regards,
Sudeep

[1] 
http://lists.infradead.org/pipermail/linux-arm-kernel/2015-July/356467.html