> -----Original Message----- > From: Alex Hung [mailto:alex.hung@xxxxxxxxxxxxx] > Sent: Monday, October 01, 2012 11:27 PM > To: Zhang, Rui > Cc: joeyli; linux-acpi@xxxxxxxxxxxxxxx > Subject: Re: [PATCH] acpi: fix brightness level is initialized to zero > when BIOS does not restore the brightness value to _BQC. > Importance: High > > Hi Rui, > > Yes the module parameter is used temporarily. However, we want to > eliminate the need of using any parameter since non-technical users > won't know them without any help. > > The question of whether lowest lowest brightness equals black screen is > debatable and I heard good / bad stories from both sides and they all > makes sense. This, however, does not necessarily play a role here. The > patch is to fix a problem - brightness is set to lowest value (not > user-friendly) when it was not intended. > > I also agree that there is nothing wrong with platform setting the > brightness to lowest level during boot and that's a side-effect of this > patch indeed.. In fact, it took me a few weeks to decide it may be an > improvement for the below reasons. > > 1. In most of cases, lowest level is less desirable or less commonly > used. If a BIOS returns uninitialized valube such as a zero in this > case, Linux causes confusion and problems to users with such platforms. > Comparing to the side-effect, this (may) benefits more users. > > 2. I also checked ACPI sepc and it says: > > B.5.4 _BQC (Brightness Query Current level) This method returns the > current brightness level of a built-in display output device. > > The definition makes it hard to argue that it is a BIOS bug not to > restore previous brightness to _BQC. I think it is ambiguous and this > small fix eliminates very dim screen (whether complete black or not) at > boot time. > > PS. This may not be relevant, but Windows restores the previous > brightness without BIOS's _BQC, Where does windows get the previous brightness? > and therefore it does not suffer from > very dim / black screen. > > Cheers, > Alex Hung > > > On 10/01/2012 09:36 PM, Zhang, Rui wrote: > > I think this is probably what you're looking for, > > > > /* > > * Some BIOSes claim they use minimum backlight at boot, > > * and this may bring dimming screen after boot > > */ > > static bool use_bios_initial_backlight = 1; > > module_param(use_bios_initial_backlight, bool, 0644); > > > > > > Lowest brightness level does not equal black screen. > > It is not a bug if a platform wants to set its brightness to lowest > brightness level during boot. > > If it IS in your case, you can use this module parameter to ignore > the initial _BQC value and use max_level instead. > > > > Thanks, > > rui > > > >> -----Original Message----- > >> From: joeyli [mailto:jlee@xxxxxxxx] > >> Sent: Monday, October 01, 2012 5:19 PM > >> To: Alex Hung > >> Cc: Zhang, Rui; linux-acpi@xxxxxxxxxxxxxxx > >> Subject: Re: [PATCH] acpi: fix brightness level is initialized to > >> zero when BIOS does not restore the brightness value to _BQC. > >> Importance: High > >> > >> 於 一，2012-10-01 於 17:11 +0800，Alex Hung 提到： > >>> On 10/01/2012 04:34 PM, joeyli wrote: > >>>> 於 一，2012-10-01 於 15:17 +0800，joeyli 提到： > >>>>> 於 一，2012-10-01 於 15:03 +0800，Alex Hung 提到： > >>>>>> On 10/01/2012 02:47 PM, joeyli wrote: > >>>>>>> Hi Alex, > >>>>>>> > >>>>>>> 於 一，2012-10-01 於 13:39 +0800，Alex Hung 提到： > >>>>>>>> Signed-off-by: Alex Hung <alex.hung@xxxxxxxxxxxxx> > >>>>>>>> --- > >>>>>>>> drivers/acpi/video.c | 4 ++++ > >>>>>>>> 1 files changed, 4 insertions(+), 0 deletions(-) > >>>>>>>> > >>>>>>>> diff --git a/drivers/acpi/video.c b/drivers/acpi/video.c index > >>>>>>>> 42b226e..eaa9573 100644 > >>>>>>>> --- a/drivers/acpi/video.c > >>>>>>>> +++ b/drivers/acpi/video.c > >>>>>>>> @@ -724,6 +724,10 @@ acpi_video_init_brightness(struct > >> acpi_video_device *device) > >>>>>>>> if (level_old == br->levels[i]) > >>>>>>>> level = level_old; > >>>>>>>> } > >>>>>>>> + > >>>>>>>> + if (level == 0) > >>>>>>>> + level = br->levels[(br->count) / 2 + 1]; > >>>>>>> > >>>>>>> Looks here used the 50% brightness level. > >>>>>>> > >>>>>>> Per comment in video.c, we want set the backlight to max_level > >>>>>>> when level_old is invalid: > >>>>>>> > >>>>>>> if (!br->flags._BQC_use_index) { > >>>>>>> /* > >>>>>>> * Set the backlight to the initial state. > >>>>>>> * On some buggy laptops, _BQC returns an > >> uninitialized value > >>>>>>> * when invoked for the first time, i.e. > >> level_old is invalid. > >>>>>>> * set the backlight to max_level in this > case > >>>>>>> */ > >>>>>>> > >>>>>>> I think here used max_level to fulfill it, e.g. > >>>>>>> > >>>>>>> + if (level == 0) > >>>>>>> + level = max_level; > >>>>>>> > >>>>>>> How do you think? > >>>>>> Hi Joey, > >>>>>> > >>>>>> I was debating with myself which level to be set, ex. 50%, ~75% > >> or > >>>>>> 100%, and I think 50% *might* be closer to normal use-case (just > >> a > >>>>>> personal guess). > >>>>>> > >>>>>> However, "max_level" seems to fit best if we treat the initial > >>>>>> zero brightness in invalid. I can modify it according it that's > >> preferred. > >>>>>> > >>>>>> Thanks for the feedback. > >>>>>> > >>>>>> Cheers, > >>>>>> Alex Hung > >>>>>> > >>>>> > >>>>> hm.... I have a question for what's the BIOS's problem that > causes > >>>>> 'level == 0'? > >>>>> That implied the issue machine's max_level is 0? > >>>>> > >>>>> /* > >>>>> * Set the level to maximum and check if _BQC uses > indexed > >> value > >>>>> */ > >>>>> result = acpi_video_device_lcd_set_level(device, > max_level); > >> /* write max_level purposely, then read level back, compare > them */ > >>>>> ... > >>>>> result = > acpi_video_device_lcd_get_level_current(device, > >> &level, 0); > >>>>> ... > >>>>> br->flags._BQC_use_index = (level == max_level ? 0 : > 1); > >>>>> if (!br->flags._BQC_use_index) { > /* > >> _BQC_use_index is 0 will run into if, means level == max_level */ > >>>>> > >>>>> So, looks the 'level == max_level == 0' when level_old is invalid. > >>>>> > >>>>> Just wonder what's defect of BIOS (in _BCL?) causes problem. > >>>>> > >>>>> > >>>> > >>>> Sorry for my misunderstood! > >>>> > >>>> I think that's possible the level_old is 0 and there have a 0 > value > >>>> in the return package from _BCL. > >>>> > >>> > >>> Yes, there is nothing wrong with _BCL and _BQC except that _BQC > >>> returns a zero initially. > >>> > >>>> Could you please share the _BCL in DSDT from issue machine? Does > >>>> there have 0 value in _BCL? > >>> > >>> _BCL returns below data and there is a zero in the list. > >>> > >>> [ 744.572289] Brightness[0] = 100 > >>> [ 744.572293] Brightness[1] = 50 > >>> [ 744.572295] Brightness[2] = 0 > >>> [ 744.572297] Brightness[3] = 10 > >>> [ 744.572299] Brightness[4] = 20 > >>> [ 744.572301] Brightness[5] = 30 > >>> [ 744.572303] Brightness[6] = 40 > >>> [ 744.572305] Brightness[7] = 50 > >>> [ 744.572306] Brightness[8] = 60 > >>> [ 744.572308] Brightness[9] = 70 > >>> [ 744.572310] Brightness[10] = 80 > >>> [ 744.572312] Brightness[11] = 90 > >>> [ 744.572314] Brightness[12] = 100 > >>> > >>> The below is the complete _BCL for references > >>> > >>> Method (_BCL, 0, Serialized) > >>> { > >>> Name (_T_0, Zero) > >>> If (_OSI ("NOT_WINP_KEY")) > >>> { > >>> While (One) > >>> { > >>> Store (LCDD, _T_0) > >>> If (LEqual (_T_0, 0x303CAF06)) > >>> { > >>> Return (AUOL) > >>> } > >>> Else > >>> { > >>> If (LEqual (_T_0, 0x1475AE0D)) > >>> { > >>> Return (CMIL) > >>> } > >>> Else > >>> { > >>> If (LEqual (_T_0, 0x033FE430)) > >>> { > >>> Return (LGDL) > >>> } > >>> Else > >>> { > >>> If (LEqual (_T_0, > >> 0x3942A34C)) > >>> { > >>> Return (SAML) > >>> } > >>> Else > >>> { > >>> Return (DEFL) > >>> } > >>> } > >>> } > >>> } > >>> > >>> Break > >>> } > >>> } > >>> Else > >>> { > >>> Return (Package (0x0D) > >>> { > >>> 0x64, > >>> 0x32, > >>> Zero, > >> > >> Yes, have Zero value in _BCL return package. > >> > >>> 0x0A, > >>> 0x14, > >>> 0x1E, > >>> 0x28, > >>> 0x32, > >>> 0x3C, > >>> 0x46, > >>> 0x50, > >>> 0x5A, > >>> 0x64 > >>> }) > >>> } > >>> } > >>> > >>> > >> > >> According to the above information, it make sense now! > >> > >> > >> Thank a lot! > >> Joey Lee > > ��.n��������+%������w��{.n�����{�����ܨ}���Ơz�j:+v�����w����ޙ��&�)ߡ�a����z�ޗ���ݢj��w�f
