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    Subject[PATCH 4.19 190/205] drm/i915/dp: Fix link retraining comment in intel_dp_long_pulse()
    Date
    4.19-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>

    commit 49af5d95b9b3c21a84ad115a9db9acbc036d849a upstream.

    Comment claims link needs to be retrained because the connected sink raised
    a long pulse to indicate link loss. If the sink did so,
    intel_dp_hotplug() would have handled link retraining. Looking at the
    logs in Bugzilla referenced in commit '3cf71bc9904d ("drm/i915: Re-apply
    Perform link quality check, unconditionally during long pulse"")', the
    issue is that the sink does not trigger an interrupt. What we want is
    ->detect() from user space to check link status and retrain. Ville's
    review for the original patch also indicates the same root cause. So,
    rewrite the comment.

    v2: Patch split and rewrote comment.

    Cc: Lyude Paul <lyude@redhat.com>
    Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
    Cc: Jani Nikula <jani.nikula@linux.intel.com>
    Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
    Cc: Jan-Marek Glogowski <glogow@fbihome.de>
    References: 3cf71bc9904d ("drm/i915: Re-apply "Perform link quality check, unconditionally during long pulse"")
    Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
    Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
    Link: https://patchwork.freedesktop.org/patch/msgid/20180927205735.16651-1-dhinakaran.pandiyan@intel.com
    (cherry picked from commit 9ebd8202393dde9d3678c9ec162c1aa63ba17eac)
    Fixes: 399334708b4f ("drm/i915: Re-apply "Perform link quality check, unconditionally during long pulse"")
    Cc: stable@vger.kernel.org
    Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/gpu/drm/i915/intel_dp.c | 13 +++----------
    1 file changed, 3 insertions(+), 10 deletions(-)

    --- a/drivers/gpu/drm/i915/intel_dp.c
    +++ b/drivers/gpu/drm/i915/intel_dp.c
    @@ -4741,16 +4741,9 @@ intel_dp_long_pulse(struct intel_connect
    goto out;
    } else {
    /*
    - * If display is now connected check links status,
    - * there has been known issues of link loss triggering
    - * long pulse.
    - *
    - * Some sinks (eg. ASUS PB287Q) seem to perform some
    - * weird HPD ping pong during modesets. So we can apparently
    - * end up with HPD going low during a modeset, and then
    - * going back up soon after. And once that happens we must
    - * retrain the link to get a picture. That's in case no
    - * userspace component reacted to intermittent HPD dip.
    + * Some external monitors do not signal loss of link
    + * synchronization with an IRQ_HPD, so force a link status
    + * check.
    */
    struct intel_encoder *encoder = &dp_to_dig_port(intel_dp)->base;


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