linux-kernel - Re: [PATCH 5/5] ARM: tegra: cpuidle: use firmware call for power down

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Message-ID: <52F2F348.3000502@nvidia.com>
Date:	Thu, 6 Feb 2014 11:28:24 +0900
From:	Alexandre Courbot <acourbot@...dia.com>
To:	Stephen Warren <swarren@...dotorg.org>,
	Alexandre Courbot <gnurou@...il.com>
CC:	Thierry Reding <thierry.reding@...il.com>,
	Russell King <linux@....linux.org.uk>,
	Olof Johansson <olof@...om.net>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5/5] ARM: tegra: cpuidle: use firmware call for power
 down

On 02/06/2014 01:28 AM, Stephen Warren wrote:
> On 01/23/2014 12:39 AM, Alexandre Courbot wrote:
>> On Thu, Jan 23, 2014 at 5:45 AM, Stephen Warren <swarren@...dotorg.org> wrote:
>>> On 01/21/2014 03:10 AM, Alexandre Courbot wrote:
>>>> Invoke the do_idle() firmware call before suspending a CPU so that the
>>>> underlying firmware (if any) can take necessary action.
>>>
>>>> diff --git a/arch/arm/mach-tegra/cpuidle-tegra114.c b/arch/arm/mach-tegra/cpuidle-tegra114.c
>>>
>>>> @@ -45,6 +46,8 @@ static int tegra114_idle_power_down(struct cpuidle_device *dev,
>>>>
>>>>        clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_ENTER, &dev->cpu);
>>>>
>>>> +     call_firmware_op(do_idle);
>>>> +
>>>>        cpu_suspend(0, tegra30_sleep_cpu_secondary_finish);
>>>>
>>>>        clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_EXIT, &dev->cpu);
>>>
>>> Don't you need to have the kernel also *not* do something when entering
>>> idle; doesn't the FW op replace some of the register writes that the
>>> kernel would otherwise be doing?
>>
>> It seems like the operation is actually to inform the firmware that we
>> are going to suspend the CPU. Downstream kernel also uses it that way.
>> But you are right in that we should expect do_idle() to actually
>> perform the suspend operation. Maybe a prepare_idle() operation should
>> be added to the firmware interface for this purpose?
>
> That sounds like a reasonable change. Is it easy to plumb in?

I think so. Will post a v2 of this soon.

Thanks,
Alex.


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