DRM: clean up and document parsing of video= parameter

The video= parameter of the DRM drivers supports some additional flags that
the normal fb drivers do not have. They also allow to limit these flags to
specific outputs. Both things were previously undocumented.

Also the parsing of the line had some oddities:
-A lot of misplaced options were silently ignored or partly rejected instead
 of stopping the parsing immediately
-The 'R' option is documented to follow the 'M' option if specified. It is not
 documented that 'M' is needed to specify 'R' (also this is the case for normal
 fb drivers). In fact the code is correct for normal fb drivers but wrong for
 DRM ones.
 The old code allowed 'R' only _before_ 'M' (since it parses backwards) and only
 if 'M' is given at all which is not needed for the DRM drivers.
-the margins option ('m') was parsed but later ignored even if the later
 functions support it.
-specifying multiple enable options at the same time did not lead to an error.
-specifying something bogus for horizontal resolution (i.e. other things as
 digits) did not lead to an error but an invalid resolution was used.

If any errors are encountered the position of the faulting string is now
printed to the user and the complete mode is ignored. This gives much
more consistent error behaviour.

I also removed some useless assignments and changed the local flag variables
to be bool.

Signed-off-by: Rolf Eike Beer <eike-kernel@sf-tec.de>
Signed-off-by: Dave Airlie <airlied@redhat.com>

1 files changed, 18 insertions, 3 deletions

diff --git a/Documentation/fb/modedb.txt b/Documentation/fb/modedb.txt
index ec4dee75a354..16aa08453911 100644
--- a/Documentation/fb/modedb.txt
+++ b/Documentation/fb/modedb.txt
@@ -20,7 +20,7 @@ in a video= option, fbmem considers that to be a global video mode option.
 
 Valid mode specifiers (mode_option argument):
 
-    <xres>x<yres>[M][R][-<bpp>][@<refresh>][i][m]
+    <xres>x<yres>[M][R][-<bpp>][@<refresh>][i][m][eDd]
     <name>[-<bpp>][@<refresh>]
 
 with <xres>, <yres>, <bpp> and <refresh> decimal numbers and <name> a string.
@@ -36,6 +36,21 @@ pixels and 1.8% of yres).
 
        Sample usage: 1024x768M@60m - CVT timing with margins
 
+DRM drivers also add options to enable or disable outputs:
+
+'e' will force the display to be enabled, i.e. it will override the detection
+if a display is connected. 'D' will force the display to be enabled and use
+digital output. This is useful for outputs that have both analog and digital
+signals (e.g. HDMI and DVI-I). For other outputs it behaves like 'e'. If 'd'
+is specified the output is disabled.
+
+You can additionally specify which output the options matches to.
+To force the VGA output to be enabled and drive a specific mode say:
+    video=VGA-1:1280x1024@60me
+
+Specifying the option multiple times for different ports is possible, e.g.:
+    video=LVDS-1:d video=HDMI-1:D
+
 ***** oOo ***** oOo ***** oOo ***** oOo ***** oOo ***** oOo ***** oOo *****
 
 What is the VESA(TM) Coordinated Video Timings (CVT)?
@@ -132,5 +147,5 @@ There may be more modes.
     tridentfb   - Trident (Cyber)blade chipset frame buffer
     vt8623fb    - VIA 8623 frame buffer
 
-BTW, only a few drivers use this at the moment. Others are to follow
-(feel free to send patches).
+BTW, only a few fb drivers use this at the moment. Others are to follow
+(feel free to send patches). The DRM drivers also support this.