linux-kernel - Re: [ath5k-devel] [PATCH v3] ath5k: disable ASPM

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Date:	Mon, 26 Jul 2010 15:20:23 -0700
From:	"Luis R. Rodriguez" <lrodriguez@...eros.com>
To:	Matthew Garrett <mjg59@...f.ucam.org>
Cc:	Maxim Levitsky <maximlevitsky@...il.com>,
	Luis Rodriguez <Luis.Rodriguez@...eros.com>,
	Bob Copeland <me@...copeland.com>,
	"Luis R. Rodriguez" <mcgrof@...badil.infradead.org>,
	Jussi Kivilinna <jussi.kivilinna@...et.fi>,
	"ath5k-devel@...ts.ath5k.org" <ath5k-devel@...ts.ath5k.org>,
	"linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	"kernel-team@...ts.ubuntu.com" <kernel-team@...ts.ubuntu.com>,
	"tim.gardner@...onical.com" <tim.gardner@...onical.com>,
	David Quan <David.Quan@...eros.com>
Subject: Re: [ath5k-devel] [PATCH v3] ath5k: disable ASPM

On Mon, Jul 26, 2010 at 2:14 PM, Matthew Garrett <mjg59@...f.ucam.org> wrote:
> On Mon, Jul 26, 2010 at 02:06:51PM -0700, Luis R. Rodriguez wrote:
>
>> No, ASPM must be enabled by the Systems Integrator through the BIOS, there are
>> other settings that have to be taken care of like modifying some PCI entrance and
>> exit latency timers, the number of FTS packets we send to exit L0s, amongst
>> other things. If a user selectively enables L1 but the BIOS had it disabled on
>> the device it may not work correctly.
>
> That's really the job of the driver.

The problem is that sometimes tweaks need to be done on the PCI
controller/root complex, not the PCIE device/endpoint. Today these
sort of changes *are* handled by the respective  systems
integrator/BIOS team and varies depending on the root complex used.
Atheros does not handle these at all in the driver.

> If the ASPM policy is set to
> powersave, the fadt doesn't indicate that ASPM should be disabled and
> the bus's _OSC method grants full control then the kernel will enable
> whatever combination of L states meet the latency constraints. If the
> hardware has additional constraints then the hardware-specific driver
> needs to handle them.

This makes sense but Is there an API for this?

> We don't rely on the BIOS to set up ASPM states. Nor does Windows.

Understood, but today some tweaks seem to be done on the BIOS
depending on the endpoint / root complex.

  Luis
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