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SubjectRe: [PATCH 0/3] drm/dp_mst: Fix bandwidth checking regressions from DSC patches
Hi Lyude,

On 3/4/20 11:36 PM, Lyude Paul wrote:
> AMD's patch series for adding DSC support to the MST helpers
> unfortunately introduced a few regressions into the kernel that I didn't
> get around to fixing until just now. I would have reverted the changes
> earlier, but seeing as that would have reverted all of amd's DSC support
> + everything that was done on top of that I realllllly wanted to avoid
> doing that.
> Anyway, this should fix everything as far as I can tell. Note that I
> don't have any DSC displays locally yet, so if someone from AMD could
> sanity check this I would appreciate it ♥.

Thank you for trying to fix this, unfortunately for me this is not fixed,
with this series. My setup:

5.6-rc4 + your 3 patches (+ some unrelated patches outside of drm)

-Lenovo x1 7th gen +
Lenovo TB3 dock gen 2 +
2 external 1920x1080@60 monitors connected to the 2 HDMI interfaces on the dock
-System booted with the LID closed, so that the firmware/BIOS has already
initialized both monitors when the kernel boots

This should be fairly easy to reproduce on a similar setup, other
users are seeing similar problems when connecting more then 1 monitor
to DP-MST docks, see e.g. :

Let me know if you want me to collect some drm.debug logs, I guess
if you do, you want me to use drm.debug=0x114 ?



> Cc: Mikita Lipski <>
> Cc: Alex Deucher <>
> Cc: Sean Paul <>
> Cc: Hans de Goede <>
> Lyude Paul (3):
> drm/dp_mst: Rename drm_dp_mst_is_dp_mst_end_device() to be less
> redundant
> drm/dp_mst: Don't show connectors as connected before probing
> available PBN
> drm/dp_mst: Rewrite and fix bandwidth limit checks
> drivers/gpu/drm/drm_dp_mst_topology.c | 124 ++++++++++++++++++++------
> 1 file changed, 96 insertions(+), 28 deletions(-)

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