summaryrefslogtreecommitdiffstats
path: root/Documentation/EDID/howto.rst
diff options
context:
space:
mode:
Diffstat (limited to 'Documentation/EDID/howto.rst')
-rw-r--r--Documentation/EDID/howto.rst58
1 files changed, 58 insertions, 0 deletions
diff --git a/Documentation/EDID/howto.rst b/Documentation/EDID/howto.rst
new file mode 100644
index 000000000000..725fd49a88ca
--- /dev/null
+++ b/Documentation/EDID/howto.rst
@@ -0,0 +1,58 @@
+:orphan:
+
+====
+EDID
+====
+
+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.
+
+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 vsyncstart-vdisp
+ #define YPULSE vsyncend-vsyncstart