Messages in this thread | | | From | Yusuf Khan <> | Date | Sat, 26 Mar 2022 21:40:12 -0700 | Subject | Re: [PATCH v9] drivers: ddcci: upstream DDCCI driver |
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Sorry for the incorrect titles, ill send another patch series shortly with everything sorted.
On Sat, Mar 26, 2022 at 9:25 PM Yusuf Khan <yusisamerican@gmail.com> wrote: > > This patch adds Documentation for the DDCCI driver. > > Signed-off-by: Yusuf Khan <yusisamerican@gmail.com> > Signed-off-by: Christoph Grenz <christophg+lkml@grenz-bonn.de> > --- > Documentation/ABI/testing/sysfs-driver-ddcci | 57 +++++++++ > Documentation/driver-api/ddcci.rst | 122 +++++++++++++++++++ > 2 files changed, 179 insertions(+) > create mode 100644 Documentation/ABI/testing/sysfs-driver-ddcci > create mode 100644 Documentation/driver-api/ddcci.rst > > diff --git a/Documentation/ABI/testing/sysfs-driver-ddcci b/Documentation/ABI/testing/sysfs-driver-ddcci > new file mode 100644 > index 000000000000..19f77ccf3ed0 > --- /dev/null > +++ b/Documentation/ABI/testing/sysfs-driver-ddcci > @@ -0,0 +1,57 @@ > +What: /sys/bus/ddcci/ddcci<I²C bus number>i<hex address> > +Date: March 2022 > +KernelVersion: 5.18 > +Contact: Christoph Grenz <christophg+lkml@grenz-bonn.de> > +Description: This file is a user interface for an internal > + dependent device on the I2C bus, it exports the same > + information as the master device(/sys/bus/ddcci/ > + ddcci<I²C bus number>) that is referenced in this > + document. > + > +What: /sys/bus/ddcci/ddcci<I²C bus number>e<hex address> > +Date: March 2022 > +KernelVersion: 5.18 > +Contact: Christoph Grenz <christophg+lkml@grenz-bonn.de> > +Description: This file is a user interface for an external > + dependent device on the I2C bus, it exports the same > + information as the master device(/sys/bus/ddcci/ > + ddcci<I²C bus number>) that is referenced in this > + document. > + > +What: /sys/bus/ddcci/ddcci<I²C bus number> > +Date: March 2022 > +KernelVersion: 5.18 > +Contact: Christoph Grenz <christophg+lkml@grenz-bonn.de> > +Description: This file provides the user interface for the > + master device on the I2C bus. It exports the following > + peices of information: > + - idProt > + ACCESS.bus protocol supported by the device. Usually > + "monitor". > + > + - idType > + ACCESS.bus device subtype. Usually "LCD" or "CRT". > + > + - idModel > + ACCESS.bus device model identifier. Usually a > + shortened form of the device model name. > + > + - idVendor > + ACCESS.bus device vendor identifier. Empty if the > + Identification command is not supported. > + > + - idModule > + ACCESS.bus device module identifier. Empty if the > + Identification command is not supported. > + > + - idSerial > + 32 bit device number. A fixed serial number if it's > + positive, a temporary serial number if negative and zero > + if the Identification command is not supported. > + > + - modalias > + A combined identifier for driver selection. It has the form: > + ddcci:<idProt>-<idType>-<idModel>-<idVendor>-<idModule>. > + All non-alphanumeric characters (including whitespace) > + in the model, vendor or module parts are replaced by > + underscores to prevent issues with software like systemd-udevd. > diff --git a/Documentation/driver-api/ddcci.rst b/Documentation/driver-api/ddcci.rst > new file mode 100644 > index 000000000000..2b7de1ac2656 > --- /dev/null > +++ b/Documentation/driver-api/ddcci.rst > @@ -0,0 +1,122 @@ > +.. SPDX-License-Identifier: GPL-2.0-or-later > + > +============== > +DDC/CI > +============== > + > +1. Introduction > +=============== > +DDC/CI is a control protocol for monitor settings supported by most > +monitors since about 2005. It is based on ACCESS.bus (an early USB predecessor). > +This could be used to create drivers that communicate with the DDCCI component, > +see ddcci-backlight for an example. > + > +2. sysfs interface > +================== > +Each detected DDC/CI device gets a directory in /sys/bus/ddcci/devices. > +The main device on a bus is named ddcci[I²C bus number]. > +Internal dependent devices are named ddcci[I²C bus number]i[hex address] > +External dependent devices are named ddcci[I²C bus number]e[hex address] > +There the following files export information about the device: > + > +capabilities > +The full ACCESS.bus capabilities string. It contains the protocol, > +type and model of the device, a list of all supported command > +codes, etc. See the ACCESS.bus spec for more information. > + > +- idProt > +ACCESS.bus protocol supported by the device. Usually "monitor". > + > +- idType > +ACCESS.bus device subtype. Usually "LCD" or "CRT". > + > +- idModel > +ACCESS.bus device model identifier. Usually a shortened form of the > +device model name. > + > +- idVendor > +ACCESS.bus device vendor identifier. Empty if the Identification command > +is not supported. > + > +- idModule > +ACCESS.bus device module identifier. Empty if the Identification command > +is not supported. > + > +- idSerial > +32 bit device number. A fixed serial number if it's positive, a temporary > +serial number if negative and zero if the > +Identification command is not supported. > + > +- modalias > +A combined identifier for driver selection. It has the form: > +ddcci:<idProt>-<idType>-<idModel>-<idVendor>-<idModule>. > +All non-alphanumeric characters (including whitespace) in the model, > +vendor or module parts are replaced by underscores to prevent issues > +with software like systemd-udevd. > + > +3. Character device interface > +============================= > +For each DDC/CI device a character device in > +/dev/bus/ddcci/[I²C bus number]/ is created, > +127 devices are assigned in total. > + > +The main device on the bus is named display. > + > +Internal dependent devices are named i[hex address] > + > +External dependent devices are named e[hex address] > + > +These character devices can be used to issue commands to a DDC/CI device > +more easily than over i2c-dev devices. They should be opened unbuffered. > +To send a command just write the command byte and the arguments with a > +single write() operation. The length byte and checksum are automatically > +calculated. > + > +To read a response use read() with a buffer big enough for the expected answer. > + > +NOTE: The maximum length of a DDC/CI message is 32 bytes. > + > +4. ddcci-backlight (monitor backlight driver) > +============================================= > +[This is not specific to the DDC/CI backlight driver, if you already dealt with > +backlight drivers, skip over this.] > + > +For each monitor that supports accessing the Backlight Level White > +or the Luminance property, a backlight device of type "raw" named like the > +corresponding ddcci device is created. You can find them in /sys/class/backlight/. > +For convenience a symlink "ddcci_backlight" on the device associated with the > +display connector in /sys/class/drm/ to the backlight device is created, as > +long as the graphics driver allows to make this association. > + > +5. Limitations > +============== > + > +-Dependent devices (sub devices using DDC/CI directly wired to the monitor, > +like Calibration devices, IR remotes, etc.) aren't automatically detected. > +You can force detection of external dependent devices by writing > +"ddcci-dependent [address]" into /sys/bus/i2c/i2c-?/new_device. > + > +There is no direct synchronization if you manually change the luminance > +with the buttons on your monitor, as this can only be realized through polling > +and some monitors close their OSD every time a DDC/CI command is received. > + > +Monitor hotplugging is not detected. You need to detach/reattach the I²C driver > +or reload the module. > + > +6. Debugging > +============ > +Both drivers use the dynamic debugging feature of the Linux kernel. > +To get detailed debugging messages, set the dyndbg module parameter. > +If you want to enable debugging permanently across reboots, create a file > +/etc/modprobe.d/ddcci.conf containing lines like the following before loading the modules: > + > +options ddcci dyndbg > +options ddcci-backlight dyndbg > + > +7. Origin > +============ > +This driver originally came from Christoph Grenz in DKMS form here: > +https://gitlab.com/ddcci-driver-linux/ddcci-driver-linux > +with multiple backups available on the wayback machine. It also > +inlcudes a example program for the usage of this driver in > +userland. > -- > 2.25.1 >
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