Re: i915 backlight

[Aaron Lu <aaron.lu@intel.com>]

On 08/01/2013 05:07 PM, Aaron Lu wrote:
> On 08/01/2013 04:12 PM, Borislav Petkov wrote:
>> On Thu, Aug 01, 2013 at 09:13:35AM +0800, Aaron Lu wrote:
>>> Can you please run acpi_listen and then press the Fn-Fx key, see if the
>>> events are correctly sent out?
>>
>> Like this?
>>
>> # acpi_listen
>> video/brightnessdown BRTDN 00000087 00000000
>> video/brightnessup BRTUP 00000086 00000000
>> video/brightnessdown BRTDN 00000087 00000000
>> video/brightnessup BRTUP 00000086 00000000
>> video/brightnessdown BRTDN 00000087 00000000
>> video/brightnessup BRTUP 00000086 00000000
>> video/brightnessdown BRTDN 00000087 00000000
>> video/brightnessup BRTUP 00000086 00000000
>> video/brightnessdown BRTDN 00000087 00000000
>> ^C
> 
> Yes, so the event is correctly sent out.
> 
>>
>>> From the bug page:
>>> https://bugzilla.kernel.org/show_bug.cgi?id=51231#c80
>>> I got the impression that both the acpi_video interface and the vendor
>>> interface thinkpad_screen are broken. So adding this cmdline here works
>>> suggests that either thinkpad_screen works or thinkpad vendor driver
>>> doesn't get loaded or doesn't create that interface for some reason.
>>>
>>> Alternatively, if the intel_backlight interface works(highly possible),
>>> you can use xorg.conf to specify the that backlight interface for X.
>>>
>>> Section "Device"
>>>         Option     "Backlight"	"intel_backlight"
>>> 	Identifier  "Card0"
>>> 	Driver      "intel"
>>> 	BusID       "PCI:0:2:0"
>>> EndSection
>>
>> Yeah, that didn't work *but* manually writing to both:
>>
>> /sys/class/backlight/acpi_video0/brightness
>>
>> and
>>
>> /sys/class/backlight/intel_backlight/brightness
>>
>> works.
> 
> Err...we have the event sent out on hotkey press and the interface also
> works, but still, using hotkey to adjust brightness level is broken...
> 
> I just found an old acer laptop that has similar issue(or even worse: on
> X starts, an almost black screen is shown and hotkey adjust doesn't
> work), I'll look into this.

Hi Jani & Daniel,

It turned out there is an integer overflow problem, and the below patch
fixed this problem on Acer Aspire 4732Z and thinkpad R61i.

From: Aaron Lu <aaron.lu@intel.com>
Subject: [PATCH] drm/i915: avoid brightness overflow when doing scale

Some card's max brightness level is pretty large, e.g. on Acer Aspire
4732Z, the max level is 989910. If user space set a large enough level
then the current scale done in intel_panel_set_backlight will cause an
integer overflow and the scaled level will be mistakenly small, leaving
user with an almost black screen. This patch fixes this problem.

Signed-off-by: Aaron Lu <aaron.lu@intel.com>
---
Since the only external user of intel_panel_set_backlight is operation
region code where the max will be a constant of 255, this patch fixes
the problem by comparing freq and max and then do things accordingly
instead of converting to 64 bits.

 drivers/gpu/drm/i915/intel_panel.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_panel.c b/drivers/gpu/drm/i915/intel_panel.c
index 67e2c1f..7c674f0 100644
--- a/drivers/gpu/drm/i915/intel_panel.c
+++ b/drivers/gpu/drm/i915/intel_panel.c
@@ -498,7 +498,10 @@ void intel_panel_set_backlight(struct drm_device *dev, u32 level, u32 max)
 	}
 
 	/* scale to hardware */
-	level = level * freq / max;
+	if (freq < max)
+		level = level * freq / max;
+	else
+		level = freq / max * level;
 
 	dev_priv->backlight.level = level;
 	if (dev_priv->backlight.device)
-- 
1.8.3.1


Hi Boris,

Since the sysfs interface works on your system, I think your problem
should be different. Can you please file a bug for this? I can provide
you with a debug patch and then see what happened. Please attach
acpidump when filing the bug.

https://bugzilla.kernel.org, ACPI/Power-Video.

Thanks,
Aaron

> 
>>
>> The ranges are different, though:
>>
>> intel_backlight/actual_brightness:1000
>> intel_backlight/bl_power:0
>> intel_backlight/brightness:1000
>> intel_backlight/max_brightness:4437
>> intel_backlight/type:raw
>>
>> acpi_video0/actual_brightness:41
>> acpi_video0/bl_power:0
>> acpi_video0/brightness:41
>> acpi_video0/max_brightness:100
>> acpi_video0/type:firmware
> 
> Yes, different interface has different brightness ranges and a value in
> one range may turn out to be the same actual brightness level of another
> value in another range.
> 
>>
>> I guess I need to write me a dirty script for now ... :-)
> 
> :-)
> 
>>
>> Thanks guys.
>>
> Thanks,
> Aaron
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