Re: [PATCH v2 04/21] drm/i915/dp: Sanitize intel_dp_get_link_train_fallback_values()

Imre Deak
2024-05-22T18:45:45Z

On Wed, May 22, 2024 at 09:23:20PM +0300, Ville Syrjälä wrote:
> On Mon, May 20, 2024 at 09:58:02PM +0300, Imre Deak wrote:
> > Reduce the indentation in intel_dp_get_link_train_fallback_values() by
> > adding separate helpers to reduce the link rate and lane count. Also
> > simplify things by passing crtc_state to the function.
> >
> > This also prepares for later patches in the patchset adding a limitation
> > on how the link params are reduced.
> >
> > Signed-off-by: Imre Deak <imre.deak@intel.com>
> > ---
> > .../drm/i915/display/intel_dp_link_training.c | 82 ++++++++++++-------
> > 1 file changed, 51 insertions(+), 31 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/display/intel_dp_link_training.c b/drivers/gpu/drm/i915/display/intel_dp_link_training.c
> > index 4db293f256896..edc970036866a 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dp_link_training.c
> > +++ b/drivers/gpu/drm/i915/display/intel_dp_link_training.c
> > @@ -1109,11 +1109,37 @@ static bool intel_dp_can_link_train_fallback_for_edp(struct intel_dp *intel_dp,
> > return true;
> > }
> >
> > +static int reduce_link_rate(struct intel_dp *intel_dp, int current_rate)
> > +{
> > + int rate_index;
> > + int new_rate;
> > +
> > + rate_index = intel_dp_rate_index(intel_dp->common_rates,
> > + intel_dp->num_common_rates,
> > + current_rate);
> > +
> > + if (rate_index <= 0)
> > + return -1;
> > +
> > + new_rate = intel_dp_common_rate(intel_dp, rate_index - 1);
> > +
> > + return new_rate;
>
> This is structured as
>
> if (bad)
> fail;
> success;
>
> > +}
> > +
> > +static int reduce_lane_count(struct intel_dp *intel_dp, int current_lane_count)
> > +{
> > + if (current_lane_count > 1)
> > + return current_lane_count >> 1;
> > +
> > + return -1;
>
> whereas this is
>
> if (ok)
> success;
> fail;
>
> I'd rearrange one of them so the logic is the same way around in both.

Ok, will change that.

> Otherwise lgtm
> Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
>
> > +}
> > +
> > static int intel_dp_get_link_train_fallback_values(struct intel_dp *intel_dp,
> > - int link_rate, u8 lane_count)
> > + const struct intel_crtc_state *crtc_state)
> > {
> > struct drm_i915_private *i915 = dp_to_i915(intel_dp);
> > - int index;
> > + int new_link_rate;
> > + int new_lane_count;
> >
> > /*
> > * TODO: Enable fallback on MST links once MST link compute can handle
> > @@ -1131,36 +1157,32 @@ static int intel_dp_get_link_train_fallback_values(struct intel_dp *intel_dp,
> > return 0;
> > }
> >
> > - index = intel_dp_rate_index(intel_dp->common_rates,
> > - intel_dp->num_common_rates,
> > - link_rate);
> > - if (index > 0) {
> > - if (intel_dp_is_edp(intel_dp) &&
> > - !intel_dp_can_link_train_fallback_for_edp(intel_dp,
> > - intel_dp_common_rate(intel_dp, index - 1),
> > - lane_count)) {
> > - drm_dbg_kms(&i915->drm,
> > - "Retrying Link training for eDP with same parameters\n");
> > - return 0;
> > - }
> > - intel_dp->link.max_rate = intel_dp_common_rate(intel_dp, index - 1);
> > - intel_dp->link.max_lane_count = lane_count;
> > - } else if (lane_count > 1) {
> > - if (intel_dp_is_edp(intel_dp) &&
> > - !intel_dp_can_link_train_fallback_for_edp(intel_dp,
> > - intel_dp_max_common_rate(intel_dp),
> > - lane_count >> 1)) {
> > - drm_dbg_kms(&i915->drm,
> > - "Retrying Link training for eDP with same parameters\n");
> > - return 0;
> > - }
> > - intel_dp->link.max_rate = intel_dp_max_common_rate(intel_dp);
> > - intel_dp->link.max_lane_count = lane_count >> 1;
> > - } else {
> > + new_lane_count = crtc_state->lane_count;
> > + new_link_rate = reduce_link_rate(intel_dp, crtc_state->port_clock);
> > + if (new_link_rate < 0) {
> > + new_lane_count = reduce_lane_count(intel_dp, crtc_state->lane_count);
> > + new_link_rate = intel_dp_max_common_rate(intel_dp);
> > + }
> > +
> > + if (new_lane_count < 0) {
> > drm_err(&i915->drm, "Link Training Unsuccessful\n");
> > return -1;
> > }
> >
> > + if (intel_dp_is_edp(intel_dp) &&
> > + !intel_dp_can_link_train_fallback_for_edp(intel_dp, new_link_rate, new_lane_count)) {
> > + drm_dbg_kms(&i915->drm,
> > + "Retrying Link training for eDP with same parameters\n");
> > + return 0;
> > + }
> > +
> > + drm_dbg_kms(&i915->drm, "Reducing link parameters from %dx%d to %dx%d\n",
> > + crtc_state->lane_count, crtc_state->port_clock,
> > + new_lane_count, new_link_rate);
> > +
> > + intel_dp->link.max_rate = new_link_rate;
> > + intel_dp->link.max_lane_count = new_lane_count;
> > +
> > return 0;
> > }
> >
> > @@ -1178,9 +1200,7 @@ static void intel_dp_schedule_fallback_link_training(struct intel_dp *intel_dp,
> > lt_dbg(intel_dp, DP_PHY_DPRX,
> > "Link Training failed with HOBL active, not enabling it from now on\n");
> > intel_dp->hobl_failed = true;
> > - } else if (intel_dp_get_link_train_fallback_values(intel_dp,
> > - crtc_state->port_clock,
> > - crtc_state->lane_count)) {
> > + } else if (intel_dp_get_link_train_fallback_values(intel_dp, crtc_state)) {
> > return;
> > }
> >
> > --
> > 2.43.3
>
> --
> Ville Syrjälä
> Intel