The EDID firmware loading mechanism introduced a few built-in EDIDs that
could be forced on any connector, bypassing the EDIDs it exposes.
While convenient, this limited set of EDIDs doesn't take into account
the connector type, and we can end up with an EDID that is completely
invalid for a given connector.
For example, the edid/800x600.bin file matches the following EDID:
edid-decode (hex):
00 ff ff ff ff ff ff 00 31 d8 00 00 00 00 00 00
05 16 01 03 6d 1b 14 78 ea 5e c0 a4 59 4a 98 25
20 50 54 01 00 00 45 40 01 01 01 01 01 01 01 01
01 01 01 01 01 01 a0 0f 20 00 31 58 1c 20 28 80
14 00 15 d0 10 00 00 1e 00 00 00 ff 00 4c 69 6e
75 78 20 23 30 0a 20 20 20 20 00 00 00 fd 00 3b
3d 24 26 05 00 0a 20 20 20 20 20 20 00 00 00 fc
00 4c 69 6e 75 78 20 53 56 47 41 0a 20 20 00 c2
----------------
Block 0, Base EDID:
EDID Structure Version & Revision: 1.3
Vendor & Product Identification:
Manufacturer: LNX
Model: 0
Made in: week 5 of 2012
Basic Display Parameters & Features:
Analog display
Signal Level Standard: 0.700 : 0.000 : 0.700 V p-p
Blank level equals black level
Sync: Separate Composite Serration
Maximum image size: 27 cm x 20 cm
Gamma: 2.20
DPMS levels: Standby Suspend Off
RGB color display
First detailed timing is the preferred timing
Color Characteristics:
Red : 0.6416, 0.3486
Green: 0.2919, 0.5957
Blue : 0.1474, 0.1250
White: 0.3125, 0.3281
Established Timings I & II:
DMT 0x09: 800x600 60.316541 Hz 4:3 37.879 kHz 40.000000 MHz
Standard Timings:
DMT 0x09: 800x600 60.316541 Hz 4:3 37.879 kHz 40.000000 MHz
Detailed Timing Descriptors:
DTD 1: 800x600 60.316541 Hz 4:3 37.879 kHz 40.000000 MHz (277 mm x 208 mm)
Hfront 40 Hsync 128 Hback 88 Hpol P
Vfront 1 Vsync 4 Vback 23 Vpol P
Display Product Serial Number: 'Linux #0'
Display Range Limits:
Monitor ranges (GTF): 59-61 Hz V, 36-38 kHz H, max dotclock 50 MHz
Display Product Name: 'Linux SVGA'
Checksum: 0xc2
So, an analog monitor EDID. However, if the connector was an HDMI
monitor for example, it breaks the HDMI specification that requires,
among other things, a digital display, the VIC 1 mode and an HDMI Forum
Vendor Specific Data Block in an CTA-861 extension.
We thus end up with a completely invalid EDID, which thus might confuse
HDMI-related code that could parse it.
After some discussions on IRC, we identified mainly two ways to fix
this:
- We can either create more EDIDs for each connector type to provide
a built-in EDID that matches the resolution passed in the name, and
still be a sensible EDID for that connector type;
- Or we can just prevent the EDID to be exposed to userspace if it's
built-in.
Or possibly both.
However, the conclusion was that maybe we just don't need the built-in
EDIDs at all and we should just get rid of them. So here we are.
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Acked-by: Pekka Paalanen <pekka.paalanen@collabora.com>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Maxime Ripard <mripard@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240221092636.691701-1-mripard@kernel.org
When both the documentation and the data files lived in
Documentation/EDID, this wasn't necessary, but both have
been moved to other directories in the meantime.
Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
This document describes actions that an admin can do, rather than
interfaces available to driver developers, so admin-guide seems to
be a more appropriate place for it.
Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
