linux/Documentation/EDID/HOWTO.txt

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drm: allow loading an EDID as firmware to override broken monitor Broken monitors and/or broken graphic boards may send erroneous or no EDID data. This also applies to broken KVM devices that are unable to correctly forward the EDID data of the connected monitor but invent their own fantasy data. This patch allows to specify an EDID data set to be used instead of probing the monitor for it. It contains built-in data sets of frequently used screen resolutions. In addition, a particular EDID data set may be provided in the /lib/firmware directory and loaded via the firmware interface. The name is passed to the kernel as module parameter of the drm_kms_helper module either when loaded options drm_kms_helper edid_firmware=edid/1280x1024.bin or as kernel commandline parameter drm_kms_helper.edid_firmware=edid/1280x1024.bin It is also possible to restrict the usage of a specified EDID data set to a particular connector. This is done by prepending the name of the connector to the name of the EDID data set using the syntax edid_firmware=[<connector>:]<edid> such as, for example, edid_firmware=DVI-I-1:edid/1920x1080.bin in which case no other connector will be affected. The built-in data sets are Resolution Name -------------------------------- 1024x768 edid/1024x768.bin 1280x1024 edid/1280x1024.bin 1680x1050 edid/1680x1050.bin 1920x1080 edid/1920x1080.bin They are ignored, if a file with the same name is available in the /lib/firmware directory. The built-in EDID data sets are based on standard timings that may not apply to a particular monitor and even crash it. Ideally, EDID data of the connected monitor should be used. They may be obtained through the drm/cardX/cardX-<connector>/edid entry in the /sys/devices PCI directory of a correctly working graphics adapter. It is even possible to specify the name of an EDID data set on-the-fly via the /sys/module interface, e.g. echo edid/myedid.bin >/sys/module/drm_kms_helper/parameters/edid_firmware The new screen mode is considered when the related kernel function is called for the first time after the change. Such calls are made when the X server is started or when the display settings dialog is opened in an already running X server. Signed-off-by: Carsten Emde <C.Emde@osadl.org> Signed-off-by: Dave Airlie <airlied@redhat.com>
2012-03-18 21:37:33 +00:00
In the good old days when graphics parameters were configured explicitly
in a file called xorg.conf, even broken hardware could be managed.
Today, with the advent of Kernel Mode Setting, a graphics board is
either correctly working because all components follow the standards -
or the computer is unusable, because the screen remains dark after
booting or it displays the wrong area. Cases when this happens are:
- The graphics board does not recognize the monitor.
- The graphics board is unable to detect any EDID data.
- The graphics board incorrectly forwards EDID data to the driver.
- The monitor sends no or bogus EDID data.
- A KVM sends its own EDID data instead of querying the connected monitor.
Adding the kernel parameter "nomodeset" helps in most cases, but causes
restrictions later on.
As a remedy for such situations, the kernel configuration item
CONFIG_DRM_LOAD_EDID_FIRMWARE was introduced. It allows to provide an
individually prepared or corrected EDID data set in the /lib/firmware
directory from where it is loaded via the firmware interface. The code
(see drivers/gpu/drm/drm_edid_load.c) contains built-in data sets for
commonly used screen resolutions (800x600, 1024x768, 1280x1024, 1600x1200,
1680x1050, 1920x1080) as binary blobs, but the kernel source tree does
not contain code to create these data. In order to elucidate the origin
of the built-in binary EDID blobs and to facilitate the creation of
individual data for a specific misbehaving monitor, commented sources
and a Makefile environment are given here.
drm: allow loading an EDID as firmware to override broken monitor Broken monitors and/or broken graphic boards may send erroneous or no EDID data. This also applies to broken KVM devices that are unable to correctly forward the EDID data of the connected monitor but invent their own fantasy data. This patch allows to specify an EDID data set to be used instead of probing the monitor for it. It contains built-in data sets of frequently used screen resolutions. In addition, a particular EDID data set may be provided in the /lib/firmware directory and loaded via the firmware interface. The name is passed to the kernel as module parameter of the drm_kms_helper module either when loaded options drm_kms_helper edid_firmware=edid/1280x1024.bin or as kernel commandline parameter drm_kms_helper.edid_firmware=edid/1280x1024.bin It is also possible to restrict the usage of a specified EDID data set to a particular connector. This is done by prepending the name of the connector to the name of the EDID data set using the syntax edid_firmware=[<connector>:]<edid> such as, for example, edid_firmware=DVI-I-1:edid/1920x1080.bin in which case no other connector will be affected. The built-in data sets are Resolution Name -------------------------------- 1024x768 edid/1024x768.bin 1280x1024 edid/1280x1024.bin 1680x1050 edid/1680x1050.bin 1920x1080 edid/1920x1080.bin They are ignored, if a file with the same name is available in the /lib/firmware directory. The built-in EDID data sets are based on standard timings that may not apply to a particular monitor and even crash it. Ideally, EDID data of the connected monitor should be used. They may be obtained through the drm/cardX/cardX-<connector>/edid entry in the /sys/devices PCI directory of a correctly working graphics adapter. It is even possible to specify the name of an EDID data set on-the-fly via the /sys/module interface, e.g. echo edid/myedid.bin >/sys/module/drm_kms_helper/parameters/edid_firmware The new screen mode is considered when the related kernel function is called for the first time after the change. Such calls are made when the X server is started or when the display settings dialog is opened in an already running X server. Signed-off-by: Carsten Emde <C.Emde@osadl.org> Signed-off-by: Dave Airlie <airlied@redhat.com>
2012-03-18 21:37:33 +00:00
To create binary EDID and C source code files from the existing data
material, simply type "make".
If you want to create your own EDID file, copy the file 1024x768.S,
replace the settings with your own data and add a new target to the
Makefile. Please note that the EDID data structure expects the timing
values in a different way as compared to the standard X11 format.
X11:
HTimings: hdisp hsyncstart hsyncend htotal
VTimings: vdisp vsyncstart vsyncend vtotal
EDID:
#define XPIX hdisp
#define XBLANK htotal-hdisp
#define XOFFSET hsyncstart-hdisp
#define XPULSE hsyncend-hsyncstart
#define YPIX vdisp
#define YBLANK vtotal-vdisp
#define YOFFSET (63+(vsyncstart-vdisp))
#define YPULSE (63+(vsyncend-vsyncstart))
The CRC value in the last line
drm: allow loading an EDID as firmware to override broken monitor Broken monitors and/or broken graphic boards may send erroneous or no EDID data. This also applies to broken KVM devices that are unable to correctly forward the EDID data of the connected monitor but invent their own fantasy data. This patch allows to specify an EDID data set to be used instead of probing the monitor for it. It contains built-in data sets of frequently used screen resolutions. In addition, a particular EDID data set may be provided in the /lib/firmware directory and loaded via the firmware interface. The name is passed to the kernel as module parameter of the drm_kms_helper module either when loaded options drm_kms_helper edid_firmware=edid/1280x1024.bin or as kernel commandline parameter drm_kms_helper.edid_firmware=edid/1280x1024.bin It is also possible to restrict the usage of a specified EDID data set to a particular connector. This is done by prepending the name of the connector to the name of the EDID data set using the syntax edid_firmware=[<connector>:]<edid> such as, for example, edid_firmware=DVI-I-1:edid/1920x1080.bin in which case no other connector will be affected. The built-in data sets are Resolution Name -------------------------------- 1024x768 edid/1024x768.bin 1280x1024 edid/1280x1024.bin 1680x1050 edid/1680x1050.bin 1920x1080 edid/1920x1080.bin They are ignored, if a file with the same name is available in the /lib/firmware directory. The built-in EDID data sets are based on standard timings that may not apply to a particular monitor and even crash it. Ideally, EDID data of the connected monitor should be used. They may be obtained through the drm/cardX/cardX-<connector>/edid entry in the /sys/devices PCI directory of a correctly working graphics adapter. It is even possible to specify the name of an EDID data set on-the-fly via the /sys/module interface, e.g. echo edid/myedid.bin >/sys/module/drm_kms_helper/parameters/edid_firmware The new screen mode is considered when the related kernel function is called for the first time after the change. Such calls are made when the X server is started or when the display settings dialog is opened in an already running X server. Signed-off-by: Carsten Emde <C.Emde@osadl.org> Signed-off-by: Dave Airlie <airlied@redhat.com>
2012-03-18 21:37:33 +00:00
#define CRC 0x55
also is a bit tricky. After a first version of the binary data set is
created, it must be checked with the "edid-decode" utility which will
drm: allow loading an EDID as firmware to override broken monitor Broken monitors and/or broken graphic boards may send erroneous or no EDID data. This also applies to broken KVM devices that are unable to correctly forward the EDID data of the connected monitor but invent their own fantasy data. This patch allows to specify an EDID data set to be used instead of probing the monitor for it. It contains built-in data sets of frequently used screen resolutions. In addition, a particular EDID data set may be provided in the /lib/firmware directory and loaded via the firmware interface. The name is passed to the kernel as module parameter of the drm_kms_helper module either when loaded options drm_kms_helper edid_firmware=edid/1280x1024.bin or as kernel commandline parameter drm_kms_helper.edid_firmware=edid/1280x1024.bin It is also possible to restrict the usage of a specified EDID data set to a particular connector. This is done by prepending the name of the connector to the name of the EDID data set using the syntax edid_firmware=[<connector>:]<edid> such as, for example, edid_firmware=DVI-I-1:edid/1920x1080.bin in which case no other connector will be affected. The built-in data sets are Resolution Name -------------------------------- 1024x768 edid/1024x768.bin 1280x1024 edid/1280x1024.bin 1680x1050 edid/1680x1050.bin 1920x1080 edid/1920x1080.bin They are ignored, if a file with the same name is available in the /lib/firmware directory. The built-in EDID data sets are based on standard timings that may not apply to a particular monitor and even crash it. Ideally, EDID data of the connected monitor should be used. They may be obtained through the drm/cardX/cardX-<connector>/edid entry in the /sys/devices PCI directory of a correctly working graphics adapter. It is even possible to specify the name of an EDID data set on-the-fly via the /sys/module interface, e.g. echo edid/myedid.bin >/sys/module/drm_kms_helper/parameters/edid_firmware The new screen mode is considered when the related kernel function is called for the first time after the change. Such calls are made when the X server is started or when the display settings dialog is opened in an already running X server. Signed-off-by: Carsten Emde <C.Emde@osadl.org> Signed-off-by: Dave Airlie <airlied@redhat.com>
2012-03-18 21:37:33 +00:00
most probably complain about a wrong CRC. Fortunately, the utility also
displays the correct CRC which must then be inserted into the source
file. After the make procedure is repeated, the EDID data set is ready
to be used.