[Bug 91789] MST (multi stream) with Asus PQ321 drm_dp_calc_pbn_mode() fails

[Bug 91789] MST (multi stream) with Asus PQ321 drm_dp_calc_pbn_mode() fails

[bugzilla-daemon]

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https://bugs.freedesktop.org/show_bug.cgi?id=91789

            Bug ID: 91789
           Summary: MST (multi stream) with Asus PQ321
                    drm_dp_calc_pbn_mode() fails
           Product: DRI
           Version: unspecified
          Hardware: x86 (IA32)
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: General
          Assignee: dri-devel@lists.freedesktop.org
          Reporter: Peter.Blum@lxco.com

If a Asus monitor PQ321 is used in MST mode it gets no signal.
This is because the function drm_dp_calc_pbn_mode() in drm_dp_mst_topology.c
returns a bad pixel bandwith number for the mode

Modeline 131:"1920x2160" 60 297000 1920 2008 2052 2200 2160 2168 2178 2250 0x48
0x5

The function return 8 and not the correct value of 1063.

Using simple u32 arithmetic in drm_dp_calc_pbn_mode() the monitor works fine.

I'm not sure if unsigned 32 bit would overflow in some cases.

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[Bug 91789] MST (multi stream) with Asus PQ321 drm_dp_calc_pbn_mode() fails

[bugzilla-daemon]

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https://bugs.freedesktop.org/show_bug.cgi?id=91789

Jani Nikula <jani.nikula@intel.com> changed:

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

--- Comment #1 from Jani Nikula <jani.nikula@intel.com> ---
Presumed fixed by

commit a9ebb3e46c7ef6112c0da466ef0954673ad36832
Author: Harry Wentland <harry.wentland@amd.com>
Date:   Fri Jan 22 17:07:26 2016 -0500

    drm/dp/mst: Calculate MST PBN with 31.32 fixed point

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