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Linux/Documentation/firmware-guide/acpi/video_extension.rst

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Diff markup

Differences between /Documentation/firmware-guide/acpi/video_extension.rst (Architecture sparc64) and /Documentation/firmware-guide/acpi/video_extension.rst (Architecture m68k)


  1 .. SPDX-License-Identifier: GPL-2.0                 1 .. SPDX-License-Identifier: GPL-2.0
  2                                                     2 
  3 =====================                               3 =====================
  4 ACPI video extensions                               4 ACPI video extensions
  5 =====================                               5 =====================
  6                                                     6 
  7 This driver implement the ACPI Extensions For       7 This driver implement the ACPI Extensions For Display Adapters for
  8 integrated graphics devices on motherboard, as      8 integrated graphics devices on motherboard, as specified in ACPI 2.0
  9 Specification, Appendix B, allowing to perform      9 Specification, Appendix B, allowing to perform some basic control like
 10 defining the video POST device, retrieving EDI     10 defining the video POST device, retrieving EDID information or to
 11 setup a video output, etc.  Note that this is      11 setup a video output, etc.  Note that this is an ref. implementation
 12 only.  It may or may not work for your integra     12 only.  It may or may not work for your integrated video device.
 13                                                    13 
 14 The ACPI video driver does 3 things regarding      14 The ACPI video driver does 3 things regarding backlight control.
 15                                                    15 
 16 Export a sysfs interface for user space to con     16 Export a sysfs interface for user space to control backlight level
 17 ==============================================     17 ==================================================================
 18                                                    18 
 19 If the ACPI table has a video device, and acpi     19 If the ACPI table has a video device, and acpi_backlight=vendor kernel
 20 command line is not present, the driver will r     20 command line is not present, the driver will register a backlight device
 21 and set the required backlight operation struc     21 and set the required backlight operation structure for it for the sysfs
 22 interface control. For every registered class      22 interface control. For every registered class device, there will be a
 23 directory named acpi_videoX under /sys/class/b     23 directory named acpi_videoX under /sys/class/backlight.
 24                                                    24 
 25 The backlight sysfs interface has a standard d     25 The backlight sysfs interface has a standard definition here:
 26 Documentation/ABI/stable/sysfs-class-backlight     26 Documentation/ABI/stable/sysfs-class-backlight.
 27                                                    27 
 28 And what ACPI video driver does is:                28 And what ACPI video driver does is:
 29                                                    29 
 30 actual_brightness:                                 30 actual_brightness:
 31   on read, control method _BQC will be evaluat     31   on read, control method _BQC will be evaluated to
 32   get the brightness level the firmware thinks     32   get the brightness level the firmware thinks it is at;
 33 bl_power:                                          33 bl_power:
 34   not implemented, will set the current bright     34   not implemented, will set the current brightness instead;
 35 brightness:                                        35 brightness:
 36   on write, control method _BCM will run to se     36   on write, control method _BCM will run to set the requested brightness level;
 37 max_brightness:                                    37 max_brightness:
 38   Derived from the _BCL package(see below);        38   Derived from the _BCL package(see below);
 39 type:                                              39 type:
 40   firmware                                         40   firmware
 41                                                    41 
 42 Note that ACPI video backlight driver will alw     42 Note that ACPI video backlight driver will always use index for
 43 brightness, actual_brightness and max_brightne     43 brightness, actual_brightness and max_brightness. So if we have
 44 the following _BCL package::                       44 the following _BCL package::
 45                                                    45 
 46         Method (_BCL, 0, NotSerialized)            46         Method (_BCL, 0, NotSerialized)
 47         {                                          47         {
 48                 Return (Package (0x0C)             48                 Return (Package (0x0C)
 49                 {                                  49                 {
 50                         0x64,                      50                         0x64,
 51                         0x32,                      51                         0x32,
 52                         0x0A,                      52                         0x0A,
 53                         0x14,                      53                         0x14,
 54                         0x1E,                      54                         0x1E,
 55                         0x28,                      55                         0x28,
 56                         0x32,                      56                         0x32,
 57                         0x3C,                      57                         0x3C,
 58                         0x46,                      58                         0x46,
 59                         0x50,                      59                         0x50,
 60                         0x5A,                      60                         0x5A,
 61                         0x64                       61                         0x64
 62                 })                                 62                 })
 63         }                                          63         }
 64                                                    64 
 65 The first two levels are for when laptop are o     65 The first two levels are for when laptop are on AC or on battery and are
 66 not used by Linux currently. The remaining 10      66 not used by Linux currently. The remaining 10 levels are supported levels
 67 that we can choose from. The applicable index      67 that we can choose from. The applicable index values are from 0 (that
 68 corresponds to the 0x0A brightness value) to 9     68 corresponds to the 0x0A brightness value) to 9 (that corresponds to the
 69 0x64 brightness value) inclusive. Each of thos     69 0x64 brightness value) inclusive. Each of those index values is regarded
 70 as a "brightness level" indicator. Thus from t     70 as a "brightness level" indicator. Thus from the user space perspective
 71 the range of available brightness levels is fr     71 the range of available brightness levels is from 0 to 9 (max_brightness)
 72 inclusive.                                         72 inclusive.
 73                                                    73 
 74 Notify user space about hotkey event               74 Notify user space about hotkey event
 75 ====================================               75 ====================================
 76                                                    76 
 77 There are generally two cases for hotkey event     77 There are generally two cases for hotkey event reporting:
 78                                                    78 
 79 i) For some laptops, when user presses the hot     79 i) For some laptops, when user presses the hotkey, a scancode will be
 80    generated and sent to user space through th     80    generated and sent to user space through the input device created by
 81    the keyboard driver as a key type input eve     81    the keyboard driver as a key type input event, with proper remap, the
 82    following key code will appear to user spac     82    following key code will appear to user space::
 83                                                    83 
 84         EV_KEY, KEY_BRIGHTNESSUP                   84         EV_KEY, KEY_BRIGHTNESSUP
 85         EV_KEY, KEY_BRIGHTNESSDOWN                 85         EV_KEY, KEY_BRIGHTNESSDOWN
 86         etc.                                       86         etc.
 87                                                    87 
 88 For this case, ACPI video driver does not need     88 For this case, ACPI video driver does not need to do anything(actually,
 89 it doesn't even know this happened).               89 it doesn't even know this happened).
 90                                                    90 
 91 ii) For some laptops, the press of the hotkey      91 ii) For some laptops, the press of the hotkey will not generate the
 92     scancode, instead, firmware will notify th     92     scancode, instead, firmware will notify the video device ACPI node
 93     about the event. The event value is define     93     about the event. The event value is defined in the ACPI spec. ACPI
 94     video driver will generate an key type inp     94     video driver will generate an key type input event according to the
 95     notify value it received and send the even     95     notify value it received and send the event to user space through the
 96     input device it created:                       96     input device it created:
 97                                                    97 
 98         =====           ==================         98         =====           ==================
 99         event           keycode                    99         event           keycode
100         =====           ==================        100         =====           ==================
101         0x86            KEY_BRIGHTNESSUP          101         0x86            KEY_BRIGHTNESSUP
102         0x87            KEY_BRIGHTNESSDOWN        102         0x87            KEY_BRIGHTNESSDOWN
103         etc.                                      103         etc.
104         =====           ==================        104         =====           ==================
105                                                   105 
106 so this would lead to the same effect as case     106 so this would lead to the same effect as case i) now.
107                                                   107 
108 Once user space tool receives this event, it c    108 Once user space tool receives this event, it can modify the backlight
109 level through the sysfs interface.                109 level through the sysfs interface.
110                                                   110 
111 Change backlight level in the kernel              111 Change backlight level in the kernel
112 ====================================              112 ====================================
113                                                   113 
114 This works for machines covered by case ii) in    114 This works for machines covered by case ii) in Section 2. Once the driver
115 received a notification, it will set the backl    115 received a notification, it will set the backlight level accordingly. This does
116 not affect the sending of event to user space,    116 not affect the sending of event to user space, they are always sent to user
117 space regardless of whether or not the video m    117 space regardless of whether or not the video module controls the backlight level
118 directly. This behaviour can be controlled thr    118 directly. This behaviour can be controlled through the brightness_switch_enabled
119 module parameter as documented in admin-guide/    119 module parameter as documented in admin-guide/kernel-parameters.rst. It is
120 recommended to disable this behaviour once a G    120 recommended to disable this behaviour once a GUI environment starts up and
121 wants to have full control of the backlight le    121 wants to have full control of the backlight level.
                                                      

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