[PATCH] ACPI / PM: Traverse video_device_list for backlight restoration

[PATCH] ACPI / PM: Traverse video_device_list for backlight restoration

[Matthias Hopf]

[-- Attachment #1: 0001-ACPI-PM-Traverse-video_device_list-for-backlight.patch --]
[-- Type: text/x-patch, Size: 1306 bytes --]

.bind_info in active_list[] is NULL by construction - and used to determine
the acpi_video_device pointer during backlight restoration during resume.

Using the list instead fixes backlight restoration for systems where the BIOS
doesn't do this by itself already.

Signed-off-by: Matthias Hopf <mhopf@suse.de>
---
 drivers/acpi/video.c |    6 +++---
 1 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/acpi/video.c b/drivers/acpi/video.c
index 9865d46..887ac2b 100644
--- a/drivers/acpi/video.c
+++ b/drivers/acpi/video.c
@@ -2346,7 +2346,6 @@ static int acpi_video_resume(struct notifier_block *nb,
 {
 	struct acpi_video_bus *video;
 	struct acpi_video_device *video_device;
-	int i;
 
 	switch (val) {
 	case PM_HIBERNATION_PREPARE:
@@ -2359,11 +2358,12 @@ static int acpi_video_resume(struct notifier_block *nb,
 
 	dev_info(&video->device->dev, "Restoring backlight state\n");
 
-	for (i = 0; i < video->attached_count; i++) {
-		video_device = video->attached_array[i].bind_info;
+	mutex_lock(&video->device_list_lock);
+	list_for_each_entry(video_device, &video->video_device_list, entry) {
 		if (video_device && video_device->backlight)
 			acpi_video_set_brightness(video_device->backlight);
 	}
+	mutex_unlock(&video->device_list_lock);
 
 	return NOTIFY_OK;
 }
-- 
1.6.0.2

Re: [PATCH] ACPI / PM: Traverse video_device_list for backlight restoration

[Matthias Hopf]

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@suse.de>      __        __   __
Maxfeldstr. 5 / 90409 Nuernberg   (_   | |  (_   |__          mat@mshopf.de
Phone +49-911-74053-715           __)  |_|  __)  |__  R & D   www.mshopf.de

Re: [PATCH] ACPI / PM: Traverse video_device_list for backlight restoration

[Zhang Rui]

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

Re: [PATCH] ACPI / PM: Traverse video_device_list for backlight restoration

[Matthias Hopf]

On Aug 04, 10 09:27:29 +0800, Zhang Rui wrote:
> On Tue, 2010-08-03 at 18:11 +0800, Matthias Hopf wrote:
> > 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.

Hm. Right. acpi_video_bus_get_one_device() is called after _enumerate().
Dunno why I didn't read this correctly.

> > 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.

Same to me.

> could you please attach the acpidump output of this laptop?

Will do.

> 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.

The most intriguing thing here is that the system starts writing to
/var/log/messages continuously, thus dmesg output is sort-of worthless.
This might be a reasonable side effect, it might be an indication of the
original issue.
I'll try to compile something for you.

Thanks

Matthias

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