On Mon, Oct 22, 2018 at 11:04:28AM -0700, Srivatsa, Anusha wrote:
>
>
> >-----Original Message-----
> >From: Ville Syrjälä [mailto:ville.syrj...@linux.intel.com]
> >Sent: Friday, October 19, 2018 4:12 PM
> >To: Navare, Manasi D <manasi.d.nav...@intel.com>
> >Cc: Srivatsa, Anusha <anusha.sriva...@intel.com>; intel-
> >g...@lists.freedesktop.org; Singh, Gaurav K <gaurav.k.si...@intel.com>; Jani
> >Nikula <jani.nik...@linux.intel.com>
> >Subject: Re: [v2 5/6] i915/dp/fec: Configure the Forward Error Correction
> >bits.
> >
> >On Fri, Oct 19, 2018 at 01:29:05PM -0700, Manasi Navare wrote:
> >> On Fri, Oct 19, 2018 at 10:58:29PM +0300, Ville Syrjälä wrote:
> >> > On Fri, Oct 19, 2018 at 12:24:43PM -0700, Manasi Navare wrote:
> >> > > On Fri, Oct 19, 2018 at 09:39:11PM +0300, Ville Syrjälä wrote:
> >> > > > On Mon, Oct 15, 2018 at 02:50:36PM -0700, Anusha Srivatsa wrote:
> >> > > > > If FEC is supported, the corresponding DP_TP_CTL register bits
> >> > > > > have to be configured.
> >> > > > >
> >> > > > > The driver has to program the FEC_ENABLE in DP_TP_CTL[30]
> >> > > > > register and wait till FEC_STATUS in DP_TP_CTL[28] is 1.
> >> > > > > Also add the warn message to make sure that the control
> >> > > > > register is already active while enabling FEC.
> >> > > > >
> >> > > > > v2:
> >> > > > > - Change commit message. Configure fec state after
> >> > > > > link training (Manasi, Gaurav)
> >> > > > > - Remove redundent checks (Manasi)
> >> > > > > - Remove the registers that get added automagically (Anusha)
> >> > > > >
> >> > > > > v3: s/intel_dp_set_fec_state()/intel_dp_enable_fec_state()
> >> > > > > (Gaurav)
> >> > > > >
> >> > > > > v4: rebased.
> >> > > > >
> >> > > > > Cc: Gaurav K Singh <gaurav.k.si...@intel.com>
> >> > > > > Cc: Jani Nikula <jani.nik...@linux.intel.com>
> >> > > > > Cc: Ville Syrjala <ville.syrj...@linux.intel.com>
> >> > > > > Cc: Manasi Navare <manasi.d.nav...@intel.com>
> >> > > > > Signed-off-by: Anusha Srivatsa <anusha.sriva...@intel.com>
> >> > > > > ---
> >> > > > > drivers/gpu/drm/i915/i915_reg.h | 2 ++
> >> > > > > drivers/gpu/drm/i915/intel_ddi.c | 2 ++
> >> > > > > drivers/gpu/drm/i915/intel_dp.c | 27
> >> > > > > +++++++++++++++++++++++++++ drivers/gpu/drm/i915/intel_drv.h
> >> > > > > | 3 ++-
> >> > > > > 4 files changed, 33 insertions(+), 1 deletion(-)
> >> > > > >
> >> > > > > diff --git a/drivers/gpu/drm/i915/i915_reg.h
> >> > > > > b/drivers/gpu/drm/i915/i915_reg.h index
> >> > > > > bcde78bc0027..c8d7fdcd7823 100644
> >> > > > > --- a/drivers/gpu/drm/i915/i915_reg.h
> >> > > > > +++ b/drivers/gpu/drm/i915/i915_reg.h
> >> > > > > @@ -9093,6 +9093,7 @@ enum skl_power_gate {
> >> > > > > #define _DP_TP_CTL_B 0x64140
> >> > > > > #define DP_TP_CTL(port) _MMIO_PORT(port, _DP_TP_CTL_A,
> >_DP_TP_CTL_B)
> >> > > > > #define DP_TP_CTL_ENABLE (1 << 31)
> >> > > > > +#define DP_TP_CTL_FEC_ENABLE (1 << 30)
> >> > > > > #define DP_TP_CTL_MODE_SST (0 << 27)
> >> > > > > #define DP_TP_CTL_MODE_MST (1 << 27)
> >> > > > > #define DP_TP_CTL_FORCE_ACT (1 << 25)
> >> > > > > @@ -9111,6 +9112,7 @@ enum skl_power_gate {
> >> > > > > #define _DP_TP_STATUS_A 0x64044
> >> > > > > #define _DP_TP_STATUS_B 0x64144
> >> > > > > #define DP_TP_STATUS(port) _MMIO_PORT(port, _DP_TP_STATUS_A,
> >> > > > > _DP_TP_STATUS_B)
> >> > > > > +#define DP_TP_STATUS_FEC_ENABLE_LIVE (1 << 28)
> >> > > > > #define DP_TP_STATUS_IDLE_DONE (1 << 25)
> >> > > > > #define DP_TP_STATUS_ACT_SENT (1 << 24)
> >> > > > > #define DP_TP_STATUS_MODE_STATUS_MST (1 << 23)
> >> > > > > diff --git a/drivers/gpu/drm/i915/intel_ddi.c
> >> > > > > b/drivers/gpu/drm/i915/intel_ddi.c
> >> > > > > index f531900165bf..67c013ea4d39 100644
> >> > > > > --- a/drivers/gpu/drm/i915/intel_ddi.c
> >> > > > > +++ b/drivers/gpu/drm/i915/intel_ddi.c
> >> > > > > @@ -2911,6 +2911,8 @@ static void intel_ddi_pre_enable_dp(struct
> >intel_encoder *encoder,
> >> > > > > DP_DECOMPRESSION_EN);
> >> > > > > intel_dp_sink_set_fec_ready(intel_dp, crtc_state,
> >DP_FEC_READY);
> >> > > > > intel_dp_start_link_train(intel_dp);
> >> > > > > + intel_dp_enable_fec_state(intel_dp, crtc_state);
> >> > > >
> >> > > > This doesn't look like the correct spot. According to the spec
> >> > > > it should be after stop_link_train() (where we set DP_TP_CTL to
> >> > > > to normal).
> >> > > >
> >> > >
> >> > > Yes I see in the display port enabling sequence page of the spec,
> >> > > that it says enable FEC after DP_TP_CTL is set to Normal. Also the
> >> > > FEC page says that this should be enabled only after ensuring that
> >> > > link training completed. So according to that this call should happen
> >> > > after
> >intel_dp_stop_link_train().
> >> > > So yes move this to after intel_dp_stop_link_training().
> >> > >
> >> > > > > +
> >> > > > > if (port != PORT_A || INTEL_GEN(dev_priv) >= 9)
> >> > > > > intel_dp_stop_link_train(intel_dp);
> >> > > > >
> >> > > > > diff --git a/drivers/gpu/drm/i915/intel_dp.c
> >> > > > > b/drivers/gpu/drm/i915/intel_dp.c index
> >> > > > > b4e8af3142a2..b9f85502d9ff 100644
> >> > > > > --- a/drivers/gpu/drm/i915/intel_dp.c
> >> > > > > +++ b/drivers/gpu/drm/i915/intel_dp.c
> >> > > > > @@ -3017,6 +3017,33 @@ void intel_dp_sink_set_fec_ready(struct
> >intel_dp *intel_dp,
> >> > > > > DRM_DEBUG_KMS("Failed to get FEC enabled in
> >sink\n"); }
> >> > > > >
> >> > > > > +void intel_dp_enable_fec_state(struct intel_dp *intel_dp,
> >> > > > > + const struct intel_crtc_state
> >> > > > > *crtc_state) {
> >> > > > > + struct drm_i915_private *dev_priv = dp_to_i915(intel_dp);
> >> > > > > + struct intel_digital_port *intel_dig_port =
> >dp_to_dig_port(intel_dp);
> >> > > > > + enum port port = intel_dig_port->base.port;
> >> > > > > + u32 val;
> >> > > > > +
> >> > > > > + /* FEC support exists for DP 1.4 only */
> >> > > > > + if (intel_dp_is_edp(intel_dp))
> >> > > > > + return;
> >> > > > > +
> >> > > > > + /* If Display Compression is not enabled, FEC need not be
> >configured */
> >> > > > > + if (!crtc_state->dsc_params.compression_enable)
> >> > > > > + return;
> >> > > > > +
> >> > > > > + val = I915_READ(DP_TP_CTL(port));
> >> > > > > + val |= DP_TP_CTL_FEC_ENABLE;
> >> > > > > + I915_WRITE(DP_TP_CTL(port), val);
> >> > > > > +
> >> > > > > + if (intel_wait_for_register(dev_priv, DP_TP_STATUS(port),
> >> > > > > + DP_TP_STATUS_FEC_ENABLE_LIVE,
> >> > > > > + DP_TP_STATUS_FEC_ENABLE_LIVE,
> >> > > > > + 1))
> >> > > > > + DRM_ERROR("Timed out waiting for FEC Enable
> >Status\n"); }
> >> > > >
> >> > > > There is no reason to stick these into intel_dp.c when the only
> >> > > > caller is in intel_ddi.c.
> >> > > >
> >> > >
> >> > > So may be move the set_dsc_state function also from intel_dp.c to
> >> > > intel_ddi.c Or does it make sense to move all these DSC related
> >> > > functions
> >including fec to intel_dsc.c?
> >> > >
> >> > > > We also seem to be missing platform checks. FEC doesn't appear
> >> > > > to be a thing prior to ICL. I guess the edp+compression_enable
> >> > > > takes care of this, but I think I'd rather stick a new
> >> > > > fec_enable bool into the crtc state. That way we get can add it to
> >> > > > the
> >state checker as well.
> >> > > >
> >> > >
> >> > > fec_enable can be added to crtc_state->dsc_params may be?
> >> >
> >> > Isn't FEC something that can be used w/o DSC too?
> >> >
> >>
> >> Nope, FEC always goes hand in hand with DSC on external DP and that
> >> DSC on external DP cannot be enabled without FEC.
> >
> >Sure, DSC needs FEC. But FEC doesn't need DSC. At least if I'm reading the
> >spec
> >correctly.
> >
> >FEC is enabled for the entire main link, so everything getting transported
> >over it
> >get FECced. DSC on the other hand operates on on a stream level. So assuming
> >a
> >MST branch device that can do FEC but can't do DSC you should be able
> >transport
> >both compressed and uncompressed streams through it simultaneously. Kinda
> >makes me think that we want to enable FEC for MST whenever the downstream
> >device supports it.
>
> FEC for MST modes is not supported for ICL platform. We could extend this for
> future platforms for branch devices that support FEC.
>
> >And I suppose we could also consider using FEC opportunistically for
> >uncompressed SST when we have the extra link bandwidth to handle the extra
> >overhead.
But I still dont understand the use of enabling FEC on uncompressed streams.
What errors are we trying to correct when the stream
is sent as is? Will it be used to correct the channel errors in that case?
Manasi
>
> Yes. The requirement though is for compressed streams. I am not sure if we
> will have to pay any power penalty for SST. Also my understanding is that if
> a few symbols in a non-compressed stream are in error, then only those
> symbols will be in error. These errors do not cause other pixels to get
> corrupted. In compressed streams, if a few symbols are in error, it can cause
> the entire slice to get corrupted. Will we be getting any much return on
> non-compressed streams?
>
> Anusha
> >>
> >> Manasi
> >>
> >> > >
> >> > > Manasi
> >> > >
> >> > > > > +
> >> > > > > /* If the sink supports it, try to set the power state
> >> > > > > appropriately */ void intel_dp_sink_dpms(struct intel_dp
> >> > > > > *intel_dp, int mode) { diff --git
> >> > > > > a/drivers/gpu/drm/i915/intel_drv.h
> >> > > > > b/drivers/gpu/drm/i915/intel_drv.h
> >> > > > > index fbc9fa06e8be..e51d612a9f42 100644
> >> > > > > --- a/drivers/gpu/drm/i915/intel_drv.h
> >> > > > > +++ b/drivers/gpu/drm/i915/intel_drv.h
> >> > > > > @@ -1532,7 +1532,6 @@ intel_encoder_current_mode(struct
> >> > > > > intel_encoder *encoder); bool intel_port_is_tc(struct
> >> > > > > drm_i915_private *dev_priv, enum port port); enum tc_port
> >intel_port_to_tc(struct drm_i915_private *dev_priv,
> >> > > > > enum port port);
> >> > > > > -
> >> > > > > enum pipe intel_get_pipe_from_connector(struct
> >> > > > > intel_connector *connector); int
> >intel_get_pipe_from_crtc_id_ioctl(struct drm_device *dev, void *data,
> >> > > > > struct drm_file *file_priv); @@ -
> >1712,6 +1711,8 @@
> >> > > > > void intel_dp_sink_set_decompression_state(struct intel_dp
> >> > > > > *intel_dp, void intel_dp_sink_set_fec_ready(struct intel_dp
> >> > > > > *intel_dp,
> >> > > > > const struct intel_crtc_state
> >*crtc_state,
> >> > > > > int state);
> >> > > > > +void intel_dp_enable_fec_state(struct intel_dp *intel_dp,
> >> > > > > + const struct intel_crtc_state
> >> > > > > *crtc_state);
> >> > > > > void intel_dp_encoder_reset(struct drm_encoder *encoder);
> >> > > > > void intel_dp_encoder_suspend(struct intel_encoder
> >> > > > > *intel_encoder); void intel_dp_encoder_destroy(struct
> >> > > > > drm_encoder *encoder);
> >> > > > > --
> >> > > > > 2.17.1
> >> > > >
> >> > > > --
> >> > > > Ville Syrjälä
> >> > > > Intel
> >> >
> >> > --
> >> > Ville Syrjälä
> >> > Intel
> >
> >--
> >Ville Syrjälä
> >Intel
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