[Bug 107281] Some DP MST hubs cause the driver to get stuck in link training clock recovery loop on hot-plugging

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=107281

Dhinakaran Pandiyan <dhinakaran.pandiyan at intel.com> changed:

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

--- Comment #2 from Dhinakaran Pandiyan <dhinakaran.pandiyan at intel.com> ---
commit 65172699a8bd9956705f71fb8b66b1068a1bb5cd
Author: Dhinakaran Pandiyan <dhinakaran.pandiyan at intel.com>
Date:   Wed Jul 18 10:19:43 2018 -0700

    drm/i915/mst: Continue state updates even if AUX writes fail.

    We are too late in the enabling sequence to back out cleanly, not updating
    state tracking variables, like intel_dp->active_mst_links in this
    instance, results in incorrect behaviour further along.

    v2: Fixed int v/s bool comparison

    Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
    Cc: Rodrigo Vivi <rodrigo.vivi at intel.com>
    Cc: Nathan Ciobanu <nathan.d.ciobanu at linux.intel.com>
    Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=107281
    Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan at intel.com>
    Reviewed-by: Nathan Ciobanu <nathan.d.ciobanu at linux.intel.com>
    Tested-by: Nathan Ciobanu <nathan.d.ciobanu at linux.intel.com>
    Reviewed-by: Rodrigo Vivi <rodrigo.vivi at intel.com>
    Link:
https://patchwork.freedesktop.org/patch/msgid/20180718171943.3246-2-dhinakaran.pandiyan@intel.com

commit 45ef40aab72e21eb81147a6e8a2bca863f0234fd
Author: Dhinakaran Pandiyan <dhinakaran.pandiyan at intel.com>
Date:   Wed Jul 18 10:19:42 2018 -0700

    drm/i915/mst: Do not retrain new links

    The short pulse handler checks if channel equalization is okay and
    goes onto retrain a link if there are active MST links. This retraining
    path is not meant for new MST connections, but due to a bug elsewhere, if
    active_mst_links is < 0 the boolean check for active_mst_links passes and
    we proceed to retrain a new link. This results in a sequence of failed link
    training attempts, most likely due to the hardware not setup for link
    training at that point i.e., missing the DDI pre_enable sequence.

    [   80.301272] [drm:intel_dp_check_mst_status] channel EQ not ok,
retraining
    [   80.301312] [drm:intel_ddi_prepare_link_retrain] *ERROR* Timeout waiting
for DDI BUF C idle bit

    The above error gives us a hint something went wrong before link
    training started.

    Check for a positive value of active_mst_links and throw in a warning for
    invalid active_mst_links as debug aid.

    Cc: Nathan Ciobanu <nathan.d.ciobanu at linux.intel.com>
    Cc: Rodrigo Vivi <rodrigo.vivi at intel.com>
    Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan at intel.com>
    Tested-by: Nathan Ciobanu <nathan.d.ciobanu at linux.intel.com>
    Reviewed-by: Rodrigo Vivi <rodrigo.vivi at intel.com>
    Link:
https://patchwork.freedesktop.org/patch/msgid/20180718171943.3246-1-dhinakaran.pandiyan@intel.com

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