On Fri, 2016-08-12 at 10:56 -0700, Manasi Navare wrote:
> On Thu, Aug 11, 2016 at 08:18:54PM -0700, Pandiyan, Dhinakaran wrote:
> > On Thu, 2016-08-11 at 15:23 -0700, Manasi Navare wrote:
> > > Intel_dp_link_is_valid() function reads the Link status registers
> > > and returns a boolean to indicate link is valid or not.
> > > If the link has lost lock and is not valid any more, link
> > > training is performed outside the function else previously trained link
> > > is retained.
> > > This gives us flexibility of checking whether link is valid and training
> > > it independently.
> > >
> > > v2:
> > > * Changed the function name from intel_dp_check_link_status()
> > > to intel_dp_link_is_valid() (Lukas Wunner)
> > > * Checks for CRTC and active CRTC are moved outside the
> > > intel_dp_link_is_valid() function (Rodrigo Vivi)
> > >
> > > Signed-off-by: Manasi Navare <manasi.d.nav...@intel.com>
> > > ---
> > > drivers/gpu/drm/i915/intel_dp.c | 56
> > > +++++++++++++++++++++++++++--------------
> > > 1 file changed, 37 insertions(+), 19 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/i915/intel_dp.c
> > > b/drivers/gpu/drm/i915/intel_dp.c
> > > index 364db90..891147d 100644
> > > --- a/drivers/gpu/drm/i915/intel_dp.c
> > > +++ b/drivers/gpu/drm/i915/intel_dp.c
> > > @@ -3881,36 +3881,33 @@ go_again:
> > > return -EINVAL;
> > > }
> > >
> > > -static void
> > > -intel_dp_check_link_status(struct intel_dp *intel_dp)
> > > +static bool
> > > +intel_dp_link_is_valid(struct intel_dp *intel_dp)
> > > {
> > > - struct intel_encoder *intel_encoder = &dp_to_dig_port(intel_dp)->base;
> > > struct drm_device *dev = intel_dp_to_dev(intel_dp);
> > > u8 link_status[DP_LINK_STATUS_SIZE];
> > >
> > > WARN_ON(!drm_modeset_is_locked(&dev->mode_config.connection_mutex));
> > >
> > > if (!intel_dp_get_link_status(intel_dp, link_status)) {
> > > - DRM_ERROR("Failed to get link status\n");
> > > - return;
> > > + DRM_DEBUG_KMS("Failed to get link status\n");
> > > + return false;
> > > }
> > >
> > > - if (!intel_encoder->base.crtc)
> > > - return;
> > > + /* Check if the link is valid by reading the bits of Link status
> > > + * registers
> > > + */
> > > + if (!drm_dp_channel_eq_ok(link_status, intel_dp->lane_count)) {
> > > + DRM_DEBUG_KMS("Channel EQ or CR not ok, need to retrain\n");
> > drm_dp_channel_eq_ok() does not check for CR. Should we just say
> > "Channel EQ not ok" to preempt ambiguity while debugging ?
>
> Actually this macro checks for DP_CHANNEL_EQ_BITS which is defined as:
> #define DP_CHANNEL_EQ_BITS (DP_LANE_CR_DONE | \
> DP_LANE_CHANNEL_EQ_DONE | \
> DP_LANE_SYMBOL_LOCKED)
> So it includes checking for Channel EQ and Clock Recovery CR bits
>
>
Thank you, I should have looked hard. I will leave this to you.
> >
> > > + return false;
> > > + }
> > >
> > > - if (!to_intel_crtc(intel_encoder->base.crtc)->active)
> > > - return;
> > > + DRM_DEBUG_KMS("Link is good, no need to retrain\n");
> > The caller does not expect us to link train anymore, I don't think we
> > have to explicitly state "no need to retrain". Also, do we need debug
> > messages if the link is good?
>
> I agree , maybe this is not needed. I will remove this
>
> >
> > > + return true;
> > >
> > > - /* if link training is requested we should perform it always */
> > > - if ((intel_dp->compliance_test_type == DP_TEST_LINK_TRAINING) ||
> > > - (!drm_dp_channel_eq_ok(link_status, intel_dp->lane_count))) {
> > > - DRM_DEBUG_KMS("%s: channel EQ not ok, retraining\n",
> > > - intel_encoder->base.name);
> > > - intel_dp_start_link_train(intel_dp);
> > > - intel_dp_stop_link_train(intel_dp);
> > > - }
> > > }
> > >
> > > +
> > > /*
> > > * According to DP spec
> > > * 5.1.2:
> > > @@ -3928,6 +3925,8 @@ static bool
> > > intel_dp_short_pulse(struct intel_dp *intel_dp)
> > > {
> > > struct drm_device *dev = intel_dp_to_dev(intel_dp);
> > > + struct intel_digital_port *intel_dig_port = dp_to_dig_port(intel_dp);
> > > + struct intel_encoder *intel_encoder = &intel_dig_port->base;
> > > u8 sink_irq_vector = 0;
> > > u8 old_sink_count = intel_dp->sink_count;
> > > bool ret;
> > > @@ -3968,8 +3967,18 @@ intel_dp_short_pulse(struct intel_dp *intel_dp)
> > > DRM_DEBUG_DRIVER("CP or sink specific irq unhandled\n");
> > > }
> > >
> > > + /* Do not train the link if there is no crtc */
> > > + if (!intel_encoder->base.crtc)
> > > + return true;
> > > + if (!to_intel_crtc(intel_encoder->base.crtc)->active)
> > > + return true;
> > > +
> > I might be completely off base here. Shouldn't we keep the link valid
> > irrespective of whether there is an active crtc? I thought that is what
> > the refactoring is supposed to enable. Does intel_dp_short_pulse() get
> > called when there is a link loss during upfront link training? And in
> > that case, shouldn't we retrain even without a crtc?
>
> We cannot ever retrain without a CRTC. This check is more for making sure
> that the clocks
> are set up befofe we try to retrain else we will see AUX channel failures.
> If I track this back in the kernel tree, this check was added to avoid the
> lock up issues on some
> platforms.
So, crtc will be active by the time we get short pulse for upfront link
training failures ?
> >
> > Besides that, how about using just one return?
> >
> > struct drm_crtc *crtc = intel_encoder->base.crtc;
> >
> > if (crtc == NULL || !to_intel_crtc(crtc)->active)
> > return true;
> >
> >
>
> The only problem with doing both these checks together is that if crtc is NULL
> then we are trying to dereference a NULL pointer in the second check.
> So it should be seuqential, check if crtc is active only if there is crtc
> available.
>
> Manasi
>
afaik the second check won't be evaluated if the first is True.
> > > drm_modeset_lock(&dev->mode_config.connection_mutex, NULL);
> > > - intel_dp_check_link_status(intel_dp);
> > > + if (!intel_dp_link_is_valid(intel_dp) ||
> > > + intel_dp->compliance_test_type == DP_TEST_LINK_TRAINING) {
> > > + intel_dp_start_link_train(intel_dp);
> > > + intel_dp_stop_link_train(intel_dp);
> > > + }
> > > drm_modeset_unlock(&dev->mode_config.connection_mutex);
> > >
> > > return true;
> > > @@ -4298,8 +4307,17 @@ intel_dp_long_pulse(struct intel_connector
> > > *intel_connector)
> > > * check links status, there has been known issues of
> > > * link loss triggerring long pulse!!!!
> > > */
> > > + /* Do not train the link if there is no crtc */
> > > + if (!intel_encoder->base.crtc)
> > > + goto out;
> > > + if (!to_intel_crtc(intel_encoder->base.crtc)->active)
> > > + goto out;
> > > +
> > > drm_modeset_lock(&dev->mode_config.connection_mutex, NULL);
> > > - intel_dp_check_link_status(intel_dp);
> > > + if (!intel_dp_link_is_valid(intel_dp)) {
> > > + intel_dp_start_link_train(intel_dp);
> > > + intel_dp_stop_link_train(intel_dp);
> > > + }
> > > drm_modeset_unlock(&dev->mode_config.connection_mutex);
> > > goto out;
> > > }
> >
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