On Fri, 18 Nov 2016, Manasi Navare <manasi.d.navare@xxxxxxxxx> wrote:
> If link training fails, then we need to fallback to lower
> link rate first and if link training fails at RBR, then
> fallback to lower lane count.
> This function finds the next lower link rate/lane count
> value after link training failure.
>
> v4:
> * Remove the redundant variable link_train_failed
> v3:
> * Remove fallback_link_rate_index variable, just obtain
> that using the helper intel_dp_link_rate_index (Jani Nikula)
> v2:
> Squash the patch that returns the link rate index (Jani Nikula)
>
> Acked-by: Tony Cheng <tony.cheng@xxxxxxx>
> Acked-by: Harry Wentland <harry.wentland@xxxxxxx>
> Cc: Ville Syrjala <ville.syrjala@xxxxxxxxxxxxxxx>
> Cc: Jani Nikula <jani.nikula@xxxxxxxxxxxxxxx>
> Cc: Daniel Vetter <daniel.vetter@xxxxxxxxx>
> Signed-off-by: Manasi Navare <manasi.d.navare@xxxxxxxxx>
> ---
> drivers/gpu/drm/i915/intel_dp.c | 40 ++++++++++++++++++++++++++++++++++++++++
> drivers/gpu/drm/i915/intel_drv.h | 4 ++++
> 2 files changed, 44 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index 90283ed..4fb89e1 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -288,6 +288,46 @@ static int intel_dp_common_rates(struct intel_dp *intel_dp,
> common_rates);
> }
>
> +static int intel_dp_link_rate_index(struct intel_dp *intel_dp,
> + int *common_rates, int link_rate)
> +{
> + int common_len;
> + int index;
> +
> + common_len = intel_dp_common_rates(intel_dp, common_rates);
> + for (index = 0; index < common_len; index++) {
> + if (link_rate == common_rates[common_len - index - 1])
> + return common_len - index - 1;
> + }
> +
> + return -1;
> +}
> +
> +int intel_dp_get_link_train_fallback_values(struct intel_dp *intel_dp,
> + int link_rate, uint8_t lane_count)
> +{
> + int common_rates[DP_MAX_SUPPORTED_RATES] = {};
> + int common_len;
> + int link_rate_index = -1;
> +
> + common_len = intel_dp_common_rates(intel_dp, common_rates);
> + link_rate_index = intel_dp_link_rate_index(intel_dp,
> + common_rates,
> + link_rate);
> + if (link_rate_index > 0) {
> + intel_dp->fallback_link_rate = common_rates[link_rate_index - 1];
> + intel_dp->fallback_lane_count = intel_dp_max_lane_count(intel_dp);
So you first try lower and lower link rates, until you're at the
lowest...
> + } else if (lane_count > 1) {
> + intel_dp->fallback_link_rate = common_rates[common_len - 1];
> + intel_dp->fallback_lane_count = lane_count >> 1;
...and then go to highest rate, double lane count, and go back back to
reducing link rate. Rinse and repeat.
Problem is, lane_count will always be > 1, and you'll keep doubling lane
count without bounds if link training persistently fails, and I don't
think you'll reach the below else branch.
I regret that I haven't caught all of these issues all at once; it is in
part testament to the fact that the state machine here is not easy to
follow.
BR,
Jani.
> + } else {
> + DRM_ERROR("Link Training Unsuccessful\n");
> + return -1;
> + }
> +
> + return 0;
> +}
> +
> static enum drm_mode_status
> intel_dp_mode_valid(struct drm_connector *connector,
> struct drm_display_mode *mode)
> diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
> index cd132c2..e1c43a9 100644
> --- a/drivers/gpu/drm/i915/intel_drv.h
> +++ b/drivers/gpu/drm/i915/intel_drv.h
> @@ -887,6 +887,8 @@ struct intel_dp {
> uint32_t DP;
> int link_rate;
> uint8_t lane_count;
> + int fallback_link_rate;
> + uint8_t fallback_lane_count;
> uint8_t sink_count;
> bool link_mst;
> bool has_audio;
> @@ -1383,6 +1385,8 @@ bool intel_dp_init_connector(struct intel_digital_port *intel_dig_port,
> void intel_dp_set_link_params(struct intel_dp *intel_dp,
> int link_rate, uint8_t lane_count,
> bool link_mst);
> +int intel_dp_get_link_train_fallback_values(struct intel_dp *intel_dp,
> + int link_rate, uint8_t lane_count);
> void intel_dp_start_link_train(struct intel_dp *intel_dp);
> void intel_dp_stop_link_train(struct intel_dp *intel_dp);
> void intel_dp_sink_dpms(struct intel_dp *intel_dp, int mode);
--
Jani Nikula, Intel Open Source Technology Center
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