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

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Date:	Wed, 04 Aug 2010 09:27:29 +0800
From:	Zhang Rui <rui.zhang@...el.com>
To:	Matthias Hopf <mhopf@...e.de>
Cc:	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>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"linux-pm@...ts.linux-foundation.org" 
	<linux-pm@...ts.linux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ACPI / PM: Traverse video_device_list for backlight
 restoration

On Tue, 2010-08-03 at 18:11 +0800, Matthias Hopf wrote:
> 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.

why? .bind_info in active_list is initialized in acpi_video_device_bind.

>   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...
> 
no, the active_list is an array in fact, which equals
acpi_video_bus->attached_array. Maybe we need to change it to a more
proper name.

I'm still wondering why the patch works for you.
could you please attach the acpidump output of this laptop?

please rebuild your kernel with CONFIG_ACPI_DEBUG=y, and reboot with
kernel parameter "acpi.debug_layer=0x10 acpi.debug_level=0x400".
and attach the dmesg output after resume, both w/ and w/o the patch you
attached.

thanks,
rui


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