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

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Date:	Wed, 05 Feb 2014 09:28:18 -0700
From:	Stephen Warren <swarren@...dotorg.org>
To:	Alexandre Courbot <gnurou@...il.com>
CC:	Alexandre Courbot <acourbot@...dia.com>,
	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 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?

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