linux-kernel - Re: Getting rid of i7300

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Message-ID: <CALCETrUb6yhLAZ5P3J86h7DVR-vq0aVD9EHTc3YRPU2E735ETg@mail.gmail.com>
Date:	Thu, 4 Jun 2015 17:31:27 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Andy Lutomirski <luto@...nel.org>
Cc:	Andy Henroid <andrew.d.henroid@...el.com>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>, X86 ML <x86@...nel.org>,
	Matthew Garrett <mjg59@...f.ucam.org>
Subject: Re: Getting rid of i7300_idle's idle notifier?

On Thu, Jun 4, 2015 at 4:32 PM, Andy Lutomirski <luto@...nel.org> wrote:
> AFAICT the sole purpose for the hideous x86_64 idle_notifier mess is
> to support i7300_idle.  IMO this junk does not belong in IRQ handling,
> etc.  Can we redo this to work in some kind of generic way?
>
> I have no idea why it makes sense to twiddle I/O AT registers in the
> beginning of whatever IRQ wakes up the CPU.
>
> Note that, if absolutely necessary, the ECX bit 0 MWAIT extension can
> be used to reliably execute code before handling interrupts that wake
> us from idle.  That is, there could be a real cpuidle driver for that
> chip that does:
>
> cli;
> poke ioat;
> mwait(ecx = 1);
> poke ioat;
> sti;
>
> Or we could delete the driver entirely.

It's even easier than that.  Just shove the hooks into
acpi_idle_do_entry or similar and remove them from every other
exit_idle call site in the kernel.

--Andy
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