[Bug 105302] [DC] - Maximum pixel clock of dual-link DVI too low for some modes

[Bug 105302] [DC] - Maximum pixel clock of dual-link DVI too low for some modes

[bugzilla-daemon]

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https://bugs.freedesktop.org/show_bug.cgi?id=105302

            Bug ID: 105302
           Summary: [DC] - Maximum pixel clock of dual-link DVI too low
                    for some modes
           Product: DRI
           Version: DRI git
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/AMDgpu
          Assignee: dri-devel@lists.freedesktop.org
          Reporter: asheldon55@gmail.com

I have a monitor that supports 2560x1440 >60hz (up to around 110hz) through the
DVI-D interface but requires pixel clocks greater than the current dual-link
limit of 330khz, with amdgpu.dc=1. Setting TMDS_MAX_PIXEL_CLOCK to 250000 in
signal_types.h works around the problem. 

amdgpu.dc=0 doesn't appear to have this limit (or the value is higher) so the
problem does not exist there.

I'm using ~ag5df's drm-next-4.17-wip branch.

There appears to be a discussion about setting a higher pixel clock limit in
this bug: https://bugs.freedesktop.org/show_bug.cgi?id=93885 but focused on
HDMI and not DVI-D, and regarding the older radeon driver.

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[Bug 105302] [DC] - Maximum pixel clock of dual-link DVI too low for some modes

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https://bugs.freedesktop.org/show_bug.cgi?id=105302

Alex Deucher <alexdeucher@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |harry.wentland@amd.com

--- Comment #1 from Alex Deucher <alexdeucher@gmail.com> ---
The non-DC code should really have limited this too.  It's probably a bug
there.  As to what the actual limit is, hopefully Harry can comment on that.

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[Bug 105302] [DC] - Maximum pixel clock of dual-link DVI too low for some modes

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https://bugs.freedesktop.org/show_bug.cgi?id=105302

--- Comment #2 from Harry Wentland <harry.wentland@amd.com> ---
I don't have the spec right now but wikipedia has a nice run-down of the DVI
bounding box: https://en.wikipedia.org/wiki/Digital_Visual_Interface#Digital

Basically 2560x1600 @ 60Hz is the highest allowed for dual-link, which is just
a tad above your 2560x1440 @ 60Hz. 110Hz at full resolution would definitely
not be supported by DVI.

What monitor are you using? Is it intended to support 110Hz at full resolution
on DVI? Could it be that this full monitor capabilities are only supported
through DP?

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[Bug 105302] [DC] - Maximum pixel clock of dual-link DVI too low for some modes

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https://bugs.freedesktop.org/show_bug.cgi?id=105302

--- Comment #3 from Andrew Sheldon <asheldon55@gmail.com> ---
(In reply to Harry Wentland from comment #2)
> I don't have the spec right now but wikipedia has a nice run-down of the DVI
> bounding box: https://en.wikipedia.org/wiki/Digital_Visual_Interface#Digital
> 
> Basically 2560x1600 @ 60Hz is the highest allowed for dual-link, which is
> just a tad above your 2560x1440 @ 60Hz. 110Hz at full resolution would
> definitely not be supported by DVI.
> 
> What monitor are you using? Is it intended to support 110Hz at full
> resolution on DVI? Could it be that this full monitor capabilities are only
> supported through DP?

It's a cheap Korean monitor that only supports DVI-D (Qnix qx2710 single input
version), and unofficially supports greater than 60hz. You're right, it's above
DVI-D spec but it would be nice to have an option to use higher pixel clocks
nevertheless. The Nvidia binary drivers have the option for ignoring the pixel
clock check so there is at least one example of this being supported in the
wild.

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[Bug 105302] [DC] - Maximum pixel clock of dual-link DVI too low for some modes

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https://bugs.freedesktop.org/show_bug.cgi?id=105302

--- Comment #4 from Harry Wentland <harry.wentland@amd.com> ---
This sounds like a feature request, rather than a bug.

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[Bug 105302] [DC] - Maximum pixel clock of dual-link DVI too low for some modes

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https://bugs.freedesktop.org/show_bug.cgi?id=105302

Alex Deucher <alexdeucher@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |enhancement

--- Comment #5 from Alex Deucher <alexdeucher@gmail.com> ---
I'd rather not support running things out of spec in the driver.  The source is
open.  If you want to adjust the code allow something like that you can.

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[Bug 105302] [DC] - Maximum pixel clock of dual-link DVI too low for some modes

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https://bugs.freedesktop.org/show_bug.cgi?id=105302

--- Comment #6 from Andrew Sheldon <asheldon55@gmail.com> ---
(In reply to Alex Deucher from comment #5)
> I'd rather not support running things out of spec in the driver.  The source
> is open.  If you want to adjust the code allow something like that you can.

Fair enough, it's simple enough to patch the source for a higher limit.

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[Bug 105302] [DC] - Maximum pixel clock of dual-link DVI too low for some modes

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https://bugs.freedesktop.org/show_bug.cgi?id=105302

Martin Peres <martin.peres@free.fr> changed:

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

--- Comment #7 from Martin Peres <martin.peres@free.fr> ---
-- GitLab Migration Automatic Message --

This bug has been migrated to freedesktop.org's GitLab instance and has been
closed from further activity.

You can subscribe and participate further through the new bug through this link
to our GitLab instance: https://gitlab.freedesktop.org/drm/amd/issues/319.

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