On Wed, Jul 18, 2018 at 10:19:42AM -0700, Dhinakaran Pandiyan wrote:
> 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.ciob...@linux.intel.com>
> Cc: Rodrigo Vivi <rodrigo.v...@intel.com>
> Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandi...@intel.com>
Tested-by: Nathan Ciobanu <nathan.d.ciob...@linux.intel.com>
> ---
> drivers/gpu/drm/i915/intel_dp.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index b45b08420c1f..2d61ff01cf51 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -4213,12 +4213,14 @@ intel_dp_check_mst_status(struct intel_dp *intel_dp)
> int ret = 0;
> int retry;
> bool handled;
> +
> + WARN_ON_ONCE(intel_dp->active_mst_links < 0);
> bret = intel_dp_get_sink_irq_esi(intel_dp, esi);
> go_again:
> if (bret == true) {
>
> /* check link status - esi[10] = 0x200c */
> - if (intel_dp->active_mst_links &&
> + if (intel_dp->active_mst_links > 0 &&
> !drm_dp_channel_eq_ok(&esi[10],
> intel_dp->lane_count)) {
> DRM_DEBUG_KMS("channel EQ not ok,
> retraining\n");
> intel_dp_start_link_train(intel_dp);
> --
> 2.17.1
>
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