linux-kernel - Re: Save and Restore Generic Interrupt Controller for System Sleep on ARM

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Message-ID: <CAGAzgspYoDwbmj+cXWQJcUmmGZshQ95-a-8gBNOtxT8L2Qm-VQ@mail.gmail.com>
Date:   Thu, 30 Nov 2017 17:21:20 -0800
From:   "dbasehore ." <dbasehore@...omium.org>
To:     Marc Zyngier <marc.zyngier@....com>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>, sudeep.holla@....com,
        Linux-pm mailing list <linux-pm@...r.kernel.org>
Subject: Re: Save and Restore Generic Interrupt Controller for System Sleep on ARM

On Thu, Nov 30, 2017 at 1:44 AM, Marc Zyngier <marc.zyngier@....com> wrote:
> On Wed, Nov 29 2017 at  2:49:18 pm GMT, "dbasehore ." <dbasehore@...omium.org> wrote:
>> There was some work in ARM Trusted Firmware to support saving and
>> restoring the Generic Interrupt Controller (GICv3) before and after
>> sleep, but it seems that the plan is to have this all in the kernel
>> now. The point of doing this is to save power during sleep. On an
>> RK3399 system, we save about 15mW by disabling the power rail that the
>> GIC is on.
>>
>> I was looking for whether anyone had anything in progress already or
>> for preferences on how to do this. Marc suggested using a device tree
>> entry to indicate the need to save and restore the GIC. There is
>> another requirement to resend MAPC commands on certain implementations
>> of the GICv3 which could be indicated by another device tree entry.
>
> Let's be precise: This is a GIC-500 requirement, and not something that
> the GICv3 architecture defines (PM is *not* part of the GICv3
> architecture).
>

Just to double check, do the register restores apply to all GICv3
designs? If so, I can put that code in the gic-v3 code instead of
breaking it out.

>> If someone does have patches, I'll be able to test and verify them on
>> my system since we've gotten things working with the ARM Trusted
>> Firmware patches.
>
> I'm not aware of any such patch that has been posted for mainline, so
> just post whatever you have and we'll take it from there.
>
> IT is hard to comment further on what you're trying to do without seeing
> the code and a description of the new API between ATF and the kernel.
>
> Thanks,
>
>         M.
> --
> Jazz is not dead, it just smell funny.