Re: [PATCH] ACPI / PM: Traverse video_device_list for backlightrestoration

From: Matthias Hopf
Date: Tue Aug 03 2010 - 06:12:04 EST

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...



Matthias Hopf <mhopf@xxxxxxx> __ __ __
Maxfeldstr. 5 / 90409 Nuernberg (_ | | (_ |__ mat@xxxxxxxxx
Phone +49-911-74053-715 __) |_| __) |__ R & D
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