On Thu, Dec 08, 2016 at 11:46:02PM +0200, Jani Nikula wrote:
> On Tue, 06 Dec 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 and limits the max
> > link_rate and lane_count values to these fallback values.
> >
> > v6:
> > * Cap the max link rate and lane count to the max
> > values obtained during fallback link training (Daniel Vetter)
> > v5:
> > * Start the fallback at the lane count value passed not
> > the max lane count (Jani Nikula)
> > 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 | 2 ++
> > 2 files changed, 42 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> > index 434dc7d..b5c7526f 100644
> > --- a/drivers/gpu/drm/i915/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/intel_dp.c
> > @@ -278,6 +278,46 @@ 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;
>
> Probably somewhere in the history of the patch series there was a time
> when it was necessary to search for the rates in reverse order. What
> possible benefit could that offer at this point?
>
The advantage here is that the link rate is more likely to match quicker
if we search in reverse order.
> > + }
> > +
> > + 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] = {};
>
> No need to initialize because you initialize it a couple of lines later.
>
Agreed
> > + int common_len;
> > + int link_rate_index = -1;
>
> No need to initialize because you initialize it a couple of lines later.
>
> > +
> > + common_len = intel_dp_common_rates(intel_dp, common_rates);
> > + link_rate_index = intel_dp_link_rate_index(intel_dp,
> > + common_rates,
> > + link_rate);
>
> Please stop and think, and don't rush each new iteration of the patches.
>
> What's wrong with the above lines? Please think about it. Answer at the
> end of the mail (*).
>
> > + if (link_rate_index > 0) {
> > + intel_dp->max_sink_link_bw = drm_dp_link_rate_to_bw_code(common_rates[link_rate_index - 1]);
> > + intel_dp->max_sink_lane_count = lane_count;
> > + } else if (lane_count > 1) {
> > + intel_dp->max_sink_link_bw = intel_dp_max_link_bw(intel_dp);
> > + intel_dp->max_sink_lane_count = lane_count >> 1;
> > + } 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 b6526ad..47e3671 100644
> > --- a/drivers/gpu/drm/i915/intel_drv.h
> > +++ b/drivers/gpu/drm/i915/intel_drv.h
> > @@ -1400,6 +1400,8 @@ 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);
>
>
> (*) You do intel_dp_common_rates(intel_dp, common_rates) twice, for no
> reason at all.
>
Actually the first call was to obtain the common_len which was needed earlier but
we no longer need it because of the simplified fallback logic modifying the
max sink link rate directly.
So yes I will remove the first call to intel_dp_common_rate()
Good catch! Thanks Jani.
Regards
Manasi
> --
> Jani Nikula, Intel Open Source Technology Center
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