linux-kernel - Re: [RFC][PATCH -mm 3/3] PM: Disable _request

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Date:	Mon, 28 May 2007 19:43:24 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	pm list <linux-pm@...ts.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Nigel Cunningham <nigel@...el.suspend2.net>,
	Pavel Machek <pavel@....cz>, Oliver Neukum <oliver@...kum.org>
Subject: Re: [RFC][PATCH -mm 3/3] PM: Disable _request_firmware before hibernation/suspend

On Monday, 28 May 2007 17:55, Alan Stern wrote:
> On Sun, 27 May 2007, Rafael J. Wysocki wrote:
> 
> > From: Rafael J. Wysocki <rjw@...k.pl>
> > 
> > Use a hibernation and suspend notifier to disable the firmware requesting
> > mechanism before a hibernation/suspend and enable it after the operation.
> 
> You're using the PM_PRE_FREEZE and PM_POST_THAW notifiers for both this 
> and the userspace helper change.  Is it your intention that drivers 
> should continue to request these services but encounter an error if the 
> request occurs at the wrong time?  Or do you expect drivers to use the 
> notifier chains to know when they shouldn't make any requests?

In fact, I'd like drivers to use notifiers to actually load the firmware into
memory before hibernation/suspend.  Namely, if there's PM_PRE_FREEZE, the
driver calls request_firmware() from within the notifier and saves the firmware
in memory for future use, if need be.  Later, when PM_POST_THAW comes, the
memory holding the firmware is released.

Unfortunately there are drivers that call request_firmware() directly from
.resume() which blocks until timeout expires and fails anyway.  I just wanted
this to fail immediately, without waiting.

> In the second case you may have a problem, because there's no 
> specification about the order in which the notifiers are sent.  The 
> service may get disabled before the driver learns it isn't available, 
> or the driver may think the service is once again available before it 
> gets enabled.

Yes.

Greetings,
Rafael
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