[Bug 86861] [rv6xx] When using a hardware KVM switch between computers EDID sometimes not detected/display goes fuzzy

[Bug 86861] [rv6xx] When using a hardware KVM switch between computers EDID sometimes not detected/display goes fuzzy

[bugzilla-daemon]

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https://bugs.freedesktop.org/show_bug.cgi?id=86861

            Bug ID: 86861
           Summary: [rv6xx] When using a hardware KVM switch between
                    computers EDID sometimes not detected/display goes
                    fuzzy
           Product: DRI
           Version: XOrg git
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/Radeon
          Assignee: dri-devel@lists.freedesktop.org
          Reporter: shawn.starr@rogers.com

kernel: 3.17.2-300.fc21.x86_6

I've noticed sometimes when using my KVM Switch when switching to the laptop. I
get fuzzy text in console w/ KMS on.

if I start X, the fuzzy display continues, a full reboot resets the display
properly.

Caught an error this time (maybe just as it was about to detect the EDID of
display)

[ 5877.852952] [drm:drm_edid_block_valid] *ERROR* EDID checksum is invalid,
remainder is 130
[ 5877.860547] Raw EDID:
[ 5877.862264]          00 ff ff ff ff ff ff 00 ff ff ff ff ff ff ff ff
[ 5877.865817]          ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
[ 5877.867201]          ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
[ 5877.870127]          ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
[ 5877.871706]          ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
[ 5877.874040]          ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
[ 5877.875309]          ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
[ 5877.876593]          ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
[ 5877.880376] [drm:radeon_vga_detect] *ERROR* VGA-1: probed a monitor but
no|invalid EDID

KVM switch model: ATEN CS-1734A (Firmware: V4.2.417 not upgraded since
purchase)

The actual EDID of the display (from Xorg log):

[   416.432] (II) RADEON(0): EDID (in hex):
[   416.432] (II) RADEON(0):    00ffffffffffff00320c00f200000000
[   416.432] (II) RADEON(0):    0011010380211578eaba709859528c28
[   416.432] (II) RADEON(0):    2550542108008180a940010101010101
[   416.432] (II) RADEON(0):    010101010101e33a805a70b032401e1e
[   416.432] (II) RADEON(0):    13004bcf100000190000000000000000
[   416.432] (II) RADEON(0):    00000000000000000000000000fe0058
[   416.432] (II) RADEON(0):    55333031043135345755310a000000fe
[   416.432] (II) RADEON(0):    00283e4c53739bbaff02010a202000aa

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[Bug 86861] [rv6xx] When using a hardware KVM switch between computers EDID sometimes not detected/display goes fuzzy

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https://bugs.freedesktop.org/show_bug.cgi?id=86861

--- Comment #1 from Christian König <deathsimple@vodafone.de> ---
Sounds like just another buggy KVM switch to me.

The basic problem is that the I²C used to read the EDID assumes that you only
have two endpoints on the wire - the display and the gfx hardware. So properly
designed KVM switches have an micro-controller which fetches the EDID from the
monitor on connect and forwards the EDID to each connected system if requested.
Otherwise you run into problems when by pure coincident two systems try to
fetch the EDID at the same time.

Without the EDID the gfx hardware has no idea what resolutions the display can
handle and most likely doesn't choose the optimal one. Easiest workaround is
manually set the necessary resolution for the display.

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[Bug 86861] [rv6xx] When using a hardware KVM switch between computers EDID sometimes not detected/display goes fuzzy

[bugzilla-daemon]

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https://bugs.freedesktop.org/show_bug.cgi?id=86861

--- Comment #2 from Shawn Starr <shawn.starr@rogers.com> ---
The newer firmware updates don't address VGA EDID detection, at least the
documentation doesn't list this.

One thought though, we don't cache the EDID information if it was previously
detected? If you switch the screen, does that effectively mean the cable is
disconnected on the other computer?

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[Bug 86861] [rv6xx] When using a hardware KVM switch between computers EDID sometimes not detected/display goes fuzzy

[bugzilla-daemon]

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https://bugs.freedesktop.org/show_bug.cgi?id=86861

Alex Deucher <alexdeucher@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |NOTOURBUG

--- Comment #3 from Alex Deucher <alexdeucher@gmail.com> ---
(In reply to Shawn Starr from comment #2)
> The newer firmware updates don't address VGA EDID detection, at least the
> documentation doesn't list this.
> 
> One thought though, we don't cache the EDID information if it was previously
> detected? If you switch the screen, does that effectively mean the cable is
> disconnected on the other computer?

For analog displays like VGA, the drm core polls every 10 seconds or so to see
if the monitor is still there since the older analog connctors like VGA do not
support hotplug like digital connectors like DVI or HDMI do.

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