linux-kernel - Re: [PATCH] ACPI / PM: Traverse video_device

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Date:	Tue, 3 Aug 2010 12:11:57 +0200
From:	Matthias Hopf <mhopf@...e.de>
To:	Zhang Rui <rui.zhang@...el.com>, Len Brown <lenb@...nel.org>,
	Matthew Garrett <mjg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Julia Lawall <julia@...u.dk>, Oliver Neukum <oneukum@...e.de>
Cc:	linux-acpi@...r.kernel.org, linux-pm@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ACPI / PM: Traverse video_device_list for backlight
	restoration

A bit of background about this patch:

acpi_video_bus_get_devices() explicitly calls acpi_video_device_enumerate()
before acpi_video_bus_get_one_device(), which does acpi_video_device_bind().

In _enumerate(), active_list[] is created, with .bind_info explicitly set to
NULL, while the related .bind_info entry in video_device_list is set to the
acpi_video_device ptr in _bind().

The .bind_info is later used in acpi_video_resume() to re-set the backlight
- but it's only evaluated on the active_list[], on which all .bind_info are
NULL by construction.  This results in backlight not being restored, if the
BIOS doesn't do this by itself already.

The patch resolves this by replacing the active_list[] traversal by a
video_device_list traversal, but due to the nature of the issue I'm unsure
whether the original issue isn't of more principal quality.  I don't understand
why the list is (partially) transformed into an array in the first place,
especially as both the array *and* the list are used in the code...

Thanks

Matthias

-- 
Matthias Hopf <mhopf@...e.de>      __        __   __
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