I'm looking at cleaning up the ACPI video driver, and found what looks
like a regression in 2.6.31. This is all from code inspection; I don't
have the hardware. I think it will not hurt users, but it should still
be looked at.
The new "ignore buggy _BQC" workaround appears to override the
_BQC_use_index workaround. This means that on some systems the sysfs
"actual_brightness" attribute will return a cached value, where
previously it would query the hardware for an up-to-date value.
> @@ -618,8 +619,15 @@ acpi_video_device_lcd_get_level_current(struct acpi_video_device *device,
>
> }
> *level += bqc_offset_aml_bug_workaround;
> - device->brightness->curr = *level;
> - return 0;
> + for (i = 2; i < device->brightness->count; i++)
> + if (device->brightness->levels[i] == *level) {
> + device->brightness->curr = *level;
> + return 0;
> + }
> + /* BQC returned an invalid level. Stop using it. */
> + ACPI_WARNING((AE_INFO, "%s returned an invalid level",
> + buf));
> + device->cap._BQC = device->cap._BCQ = 0;
I believe this change will break the detection of _BQC_use_index in
acpi_video_init_brightness():
/*
* Set the level to maximum and check if _BQC uses indexed value
*/
result = acpi_video_device_lcd_set_level(device, max_level);
if (result)
goto out_free_levels;
result = acpi_video_device_lcd_get_level_current(device, &level);
if (result)
goto out_free_levels;
br->flags._BQC_use_index = (level == max_level ? 0 : 1);
If _BQC returns an index, then the value it returns won't be present in
_BCL. The initial call to get_level_current() will consider the _BQC
value invalid and disable _BQC - because we haven't had a chance to set
_BQC_use_index yet.
I think the _BQC_use_index detection needs a "raw" version of
get_level_current(), which omits the validity check. Would you like a
patch?
Regards
Alan
--
To unsubscribe from this list: send the line "unsubscribe linux-acpi" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
