[v3] drm/i915: Disable fast link training if DP config changes

Submitted by Kahola, Mika on Dec. 16, 2015, 12:26 p.m.

Details

Message ID 1450268818-6065-1-git-send-email-mika.kahola@intel.com
State New
Headers show
Series "drm/i915: Disable fast link training if DP config changes" ( rev: 2 ) in Intel GFX

Browsing this patch as part of:
"drm/i915: Disable fast link training if DP config changes" rev 2 in Intel GFX
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Commit Message

Kahola, Mika Dec. 16, 2015, 12:26 p.m.
Disable DP fast link training if DP link configuration
changes. If one of the DP link parameters i.e. link
bandwidth, lane count, rate selection, port clock or bpp
changes the link training does no longer apply the
previously computed voltage swing and pre-emphasis values.
Instead, the link training is started with zero values.

v3: Remove cached old link parameters. Instead, disable
    fast link training feature when link parameters are
    set (Ville)

v2: Readout DPCD register to check if no aux handshaking is
    required in link training (Ander)

Signed-off-by: Mika Kahola <mika.kahola@intel.com>
---
 drivers/gpu/drm/i915/intel_dp.c               |  3 ++-
 drivers/gpu/drm/i915/intel_dp_link_training.c | 16 ++++++++++++++++
 drivers/gpu/drm/i915/intel_drv.h              |  1 +
 3 files changed, 19 insertions(+), 1 deletion(-)

Patch hide | download patch | download mbox

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 31ba241..92adf21 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -1679,6 +1679,7 @@  void intel_dp_set_link_params(struct intel_dp *intel_dp,
 {
 	intel_dp->link_rate = pipe_config->port_clock;
 	intel_dp->lane_count = pipe_config->lane_count;
+	intel_dp->train_set_valid = false;
 }
 
 static void intel_dp_prepare(struct intel_encoder *encoder)
@@ -3849,7 +3850,7 @@  intel_dp_link_down(struct intel_dp *intel_dp)
 	intel_dp->DP = DP;
 }
 
-static bool
+bool
 intel_dp_get_dpcd(struct intel_dp *intel_dp)
 {
 	struct intel_digital_port *dig_port = dp_to_dig_port(intel_dp);
diff --git a/drivers/gpu/drm/i915/intel_dp_link_training.c b/drivers/gpu/drm/i915/intel_dp_link_training.c
index 8888793..0e95a98 100644
--- a/drivers/gpu/drm/i915/intel_dp_link_training.c
+++ b/drivers/gpu/drm/i915/intel_dp_link_training.c
@@ -85,6 +85,22 @@  static bool
 intel_dp_reset_link_train(struct intel_dp *intel_dp,
 			uint8_t dp_train_pat)
 {
+	bool has_dpcd;
+	bool flt_supported = false;
+
+	has_dpcd = intel_dp_get_dpcd(intel_dp);
+
+	if (has_dpcd) {
+		if (intel_dp->dpcd[DP_DPCD_REV] >= 0x11)
+			flt_supported = (intel_dp->dpcd[DP_MAX_DOWNSPREAD] &
+					 DP_NO_AUX_HANDSHAKE_LINK_TRAINING);
+	}
+
+	intel_dp->train_set_valid &= flt_supported;
+
+	DRM_DEBUG_KMS("fast link training enabled: %s\n",
+		      intel_dp->train_set_valid ? "true" : "false");
+
 	if (!intel_dp->train_set_valid)
 		memset(intel_dp->train_set, 0, sizeof(intel_dp->train_set));
 	intel_dp_set_signal_levels(intel_dp);
diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index 798463e..94041fd 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -1239,6 +1239,7 @@  int intel_dp_sink_crc(struct intel_dp *intel_dp, u8 *crc);
 bool intel_dp_compute_config(struct intel_encoder *encoder,
 			     struct intel_crtc_state *pipe_config);
 bool intel_dp_is_edp(struct drm_device *dev, enum port port);
+bool intel_dp_get_dpcd(struct intel_dp *intel_dp);
 enum irqreturn intel_dp_hpd_pulse(struct intel_digital_port *intel_dig_port,
 				  bool long_hpd);
 void intel_edp_backlight_on(struct intel_dp *intel_dp);

Comments

On Wed, Dec 16, 2015 at 02:26:58PM +0200, Mika Kahola wrote:
> Disable DP fast link training if DP link configuration
> changes. If one of the DP link parameters i.e. link
> bandwidth, lane count, rate selection, port clock or bpp
> changes the link training does no longer apply the
> previously computed voltage swing and pre-emphasis values.
> Instead, the link training is started with zero values.
> 
> v3: Remove cached old link parameters. Instead, disable
>     fast link training feature when link parameters are
>     set (Ville)
> 
> v2: Readout DPCD register to check if no aux handshaking is
>     required in link training (Ander)
> 
> Signed-off-by: Mika Kahola <mika.kahola@intel.com>
> ---
>  drivers/gpu/drm/i915/intel_dp.c               |  3 ++-
>  drivers/gpu/drm/i915/intel_dp_link_training.c | 16 ++++++++++++++++
>  drivers/gpu/drm/i915/intel_drv.h              |  1 +
>  3 files changed, 19 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index 31ba241..92adf21 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -1679,6 +1679,7 @@ void intel_dp_set_link_params(struct intel_dp *intel_dp,
>  {
>  	intel_dp->link_rate = pipe_config->port_clock;
>  	intel_dp->lane_count = pipe_config->lane_count;
> +	intel_dp->train_set_valid = false;

This would disable the optimization every time we fire up the link.
You would have to check the new vs. current params first, and clear
the flag only if there's a difference.

>  }
>  
>  static void intel_dp_prepare(struct intel_encoder *encoder)
> @@ -3849,7 +3850,7 @@ intel_dp_link_down(struct intel_dp *intel_dp)
>  	intel_dp->DP = DP;
>  }
>  
> -static bool
> +bool
>  intel_dp_get_dpcd(struct intel_dp *intel_dp)
>  {
>  	struct intel_digital_port *dig_port = dp_to_dig_port(intel_dp);
> diff --git a/drivers/gpu/drm/i915/intel_dp_link_training.c b/drivers/gpu/drm/i915/intel_dp_link_training.c
> index 8888793..0e95a98 100644
> --- a/drivers/gpu/drm/i915/intel_dp_link_training.c
> +++ b/drivers/gpu/drm/i915/intel_dp_link_training.c
> @@ -85,6 +85,22 @@ static bool
>  intel_dp_reset_link_train(struct intel_dp *intel_dp,
>  			uint8_t dp_train_pat)
>  {
> +	bool has_dpcd;
> +	bool flt_supported = false;
> +
> +	has_dpcd = intel_dp_get_dpcd(intel_dp);
> +
> +	if (has_dpcd) {
> +		if (intel_dp->dpcd[DP_DPCD_REV] >= 0x11)
> +			flt_supported = (intel_dp->dpcd[DP_MAX_DOWNSPREAD] &
> +					 DP_NO_AUX_HANDSHAKE_LINK_TRAINING);
> +	}
> +
> +	intel_dp->train_set_valid &= flt_supported;

AFAIK what we do isn't really fast link training. Fast link training is
where you skip the AUX communication entirely, ie. just send the training
patterns for a shot predefined time, and afterwards checks if the link
is in good condition or not.

> +
> +	DRM_DEBUG_KMS("fast link training enabled: %s\n",
> +		      intel_dp->train_set_valid ? "true" : "false");
> +
>  	if (!intel_dp->train_set_valid)
>  		memset(intel_dp->train_set, 0, sizeof(intel_dp->train_set));
>  	intel_dp_set_signal_levels(intel_dp);
> diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
> index 798463e..94041fd 100644
> --- a/drivers/gpu/drm/i915/intel_drv.h
> +++ b/drivers/gpu/drm/i915/intel_drv.h
> @@ -1239,6 +1239,7 @@ int intel_dp_sink_crc(struct intel_dp *intel_dp, u8 *crc);
>  bool intel_dp_compute_config(struct intel_encoder *encoder,
>  			     struct intel_crtc_state *pipe_config);
>  bool intel_dp_is_edp(struct drm_device *dev, enum port port);
> +bool intel_dp_get_dpcd(struct intel_dp *intel_dp);
>  enum irqreturn intel_dp_hpd_pulse(struct intel_digital_port *intel_dig_port,
>  				  bool long_hpd);
>  void intel_edp_backlight_on(struct intel_dp *intel_dp);
> -- 
> 1.9.1
> 
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx@lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/intel-gfx
On Wed, 2015-12-16 at 14:41 +0200, Ville Syrjälä wrote:
> On Wed, Dec 16, 2015 at 02:26:58PM +0200, Mika Kahola wrote:
> > Disable DP fast link training if DP link configuration
> > changes. If one of the DP link parameters i.e. link
> > bandwidth, lane count, rate selection, port clock or bpp
> > changes the link training does no longer apply the
> > previously computed voltage swing and pre-emphasis values.
> > Instead, the link training is started with zero values.
> > 
> > v3: Remove cached old link parameters. Instead, disable
> >     fast link training feature when link parameters are
> >     set (Ville)
> > 
> > v2: Readout DPCD register to check if no aux handshaking is
> >     required in link training (Ander)
> > 
> > Signed-off-by: Mika Kahola <mika.kahola@intel.com>
> > ---
> >  drivers/gpu/drm/i915/intel_dp.c               |  3 ++-
> >  drivers/gpu/drm/i915/intel_dp_link_training.c | 16 ++++++++++++++++
> >  drivers/gpu/drm/i915/intel_drv.h              |  1 +
> >  3 files changed, 19 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> > index 31ba241..92adf21 100644
> > --- a/drivers/gpu/drm/i915/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/intel_dp.c
> > @@ -1679,6 +1679,7 @@ void intel_dp_set_link_params(struct intel_dp *intel_dp,
> >  {
> >  	intel_dp->link_rate = pipe_config->port_clock;
> >  	intel_dp->lane_count = pipe_config->lane_count;
> > +	intel_dp->train_set_valid = false;
> 
> This would disable the optimization every time we fire up the link.
> You would have to check the new vs. current params first, and clear
> the flag only if there's a difference.
Yeah, you're right. A step too far..

> >  }
> >  
> >  static void intel_dp_prepare(struct intel_encoder *encoder)
> > @@ -3849,7 +3850,7 @@ intel_dp_link_down(struct intel_dp *intel_dp)
> >  	intel_dp->DP = DP;
> >  }
> >  
> > -static bool
> > +bool
> >  intel_dp_get_dpcd(struct intel_dp *intel_dp)
> >  {
> >  	struct intel_digital_port *dig_port = dp_to_dig_port(intel_dp);
> > diff --git a/drivers/gpu/drm/i915/intel_dp_link_training.c b/drivers/gpu/drm/i915/intel_dp_link_training.c
> > index 8888793..0e95a98 100644
> > --- a/drivers/gpu/drm/i915/intel_dp_link_training.c
> > +++ b/drivers/gpu/drm/i915/intel_dp_link_training.c
> > @@ -85,6 +85,22 @@ static bool
> >  intel_dp_reset_link_train(struct intel_dp *intel_dp,
> >  			uint8_t dp_train_pat)
> >  {
> > +	bool has_dpcd;
> > +	bool flt_supported = false;
> > +
> > +	has_dpcd = intel_dp_get_dpcd(intel_dp);
> > +
> > +	if (has_dpcd) {
> > +		if (intel_dp->dpcd[DP_DPCD_REV] >= 0x11)
> > +			flt_supported = (intel_dp->dpcd[DP_MAX_DOWNSPREAD] &
> > +					 DP_NO_AUX_HANDSHAKE_LINK_TRAINING);
> > +	}
> > +
> > +	intel_dp->train_set_valid &= flt_supported;
> 
> AFAIK what we do isn't really fast link training. Fast link training is
> where you skip the AUX communication entirely, ie. just send the training
> patterns for a shot predefined time, and afterwards checks if the link
> is in good condition or not.
> 
I know this is not exactly what the spec defines as a fast link
training. I should do a better job on naming this.

> > +
> > +	DRM_DEBUG_KMS("fast link training enabled: %s\n",
> > +		      intel_dp->train_set_valid ? "true" : "false");
> > +
> >  	if (!intel_dp->train_set_valid)
> >  		memset(intel_dp->train_set, 0, sizeof(intel_dp->train_set));
> >  	intel_dp_set_signal_levels(intel_dp);
> > diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
> > index 798463e..94041fd 100644
> > --- a/drivers/gpu/drm/i915/intel_drv.h
> > +++ b/drivers/gpu/drm/i915/intel_drv.h
> > @@ -1239,6 +1239,7 @@ int intel_dp_sink_crc(struct intel_dp *intel_dp, u8 *crc);
> >  bool intel_dp_compute_config(struct intel_encoder *encoder,
> >  			     struct intel_crtc_state *pipe_config);
> >  bool intel_dp_is_edp(struct drm_device *dev, enum port port);
> > +bool intel_dp_get_dpcd(struct intel_dp *intel_dp);
> >  enum irqreturn intel_dp_hpd_pulse(struct intel_digital_port *intel_dig_port,
> >  				  bool long_hpd);
> >  void intel_edp_backlight_on(struct intel_dp *intel_dp);
> > -- 
> > 1.9.1
> > 
> > _______________________________________________
> > Intel-gfx mailing list
> > Intel-gfx@lists.freedesktop.org
> > http://lists.freedesktop.org/mailman/listinfo/intel-gfx
>
On Wed, Dec 16, 2015 at 03:04:47PM +0200, Mika Kahola wrote:
> On Wed, 2015-12-16 at 14:41 +0200, Ville Syrjälä wrote:
> > On Wed, Dec 16, 2015 at 02:26:58PM +0200, Mika Kahola wrote:
> > > Disable DP fast link training if DP link configuration
> > > changes. If one of the DP link parameters i.e. link
> > > bandwidth, lane count, rate selection, port clock or bpp
> > > changes the link training does no longer apply the
> > > previously computed voltage swing and pre-emphasis values.
> > > Instead, the link training is started with zero values.
> > > 
> > > v3: Remove cached old link parameters. Instead, disable
> > >     fast link training feature when link parameters are
> > >     set (Ville)
> > > 
> > > v2: Readout DPCD register to check if no aux handshaking is
> > >     required in link training (Ander)
> > > 
> > > Signed-off-by: Mika Kahola <mika.kahola@intel.com>
> > > ---
> > >  drivers/gpu/drm/i915/intel_dp.c               |  3 ++-
> > >  drivers/gpu/drm/i915/intel_dp_link_training.c | 16 ++++++++++++++++
> > >  drivers/gpu/drm/i915/intel_drv.h              |  1 +
> > >  3 files changed, 19 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> > > index 31ba241..92adf21 100644
> > > --- a/drivers/gpu/drm/i915/intel_dp.c
> > > +++ b/drivers/gpu/drm/i915/intel_dp.c
> > > @@ -1679,6 +1679,7 @@ void intel_dp_set_link_params(struct intel_dp *intel_dp,
> > >  {
> > >  	intel_dp->link_rate = pipe_config->port_clock;
> > >  	intel_dp->lane_count = pipe_config->lane_count;
> > > +	intel_dp->train_set_valid = false;
> > 
> > This would disable the optimization every time we fire up the link.
> > You would have to check the new vs. current params first, and clear
> > the flag only if there's a difference.
> Yeah, you're right. A step too far..

Or should we clear in the detection code upon hotplug? Lane reversal, usb
type C and stuff like that need to probe the link in there too.
-Daniel
On Wed, Dec 16, 2015 at 02:49:51PM +0100, Daniel Vetter wrote:
> On Wed, Dec 16, 2015 at 03:04:47PM +0200, Mika Kahola wrote:
> > On Wed, 2015-12-16 at 14:41 +0200, Ville Syrjälä wrote:
> > > On Wed, Dec 16, 2015 at 02:26:58PM +0200, Mika Kahola wrote:
> > > > Disable DP fast link training if DP link configuration
> > > > changes. If one of the DP link parameters i.e. link
> > > > bandwidth, lane count, rate selection, port clock or bpp
> > > > changes the link training does no longer apply the
> > > > previously computed voltage swing and pre-emphasis values.
> > > > Instead, the link training is started with zero values.
> > > > 
> > > > v3: Remove cached old link parameters. Instead, disable
> > > >     fast link training feature when link parameters are
> > > >     set (Ville)
> > > > 
> > > > v2: Readout DPCD register to check if no aux handshaking is
> > > >     required in link training (Ander)
> > > > 
> > > > Signed-off-by: Mika Kahola <mika.kahola@intel.com>
> > > > ---
> > > >  drivers/gpu/drm/i915/intel_dp.c               |  3 ++-
> > > >  drivers/gpu/drm/i915/intel_dp_link_training.c | 16 ++++++++++++++++
> > > >  drivers/gpu/drm/i915/intel_drv.h              |  1 +
> > > >  3 files changed, 19 insertions(+), 1 deletion(-)
> > > > 
> > > > diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> > > > index 31ba241..92adf21 100644
> > > > --- a/drivers/gpu/drm/i915/intel_dp.c
> > > > +++ b/drivers/gpu/drm/i915/intel_dp.c
> > > > @@ -1679,6 +1679,7 @@ void intel_dp_set_link_params(struct intel_dp *intel_dp,
> > > >  {
> > > >  	intel_dp->link_rate = pipe_config->port_clock;
> > > >  	intel_dp->lane_count = pipe_config->lane_count;
> > > > +	intel_dp->train_set_valid = false;
> > > 
> > > This would disable the optimization every time we fire up the link.
> > > You would have to check the new vs. current params first, and clear
> > > the flag only if there's a difference.
> > Yeah, you're right. A step too far..
> 
> Or should we clear in the detection code upon hotplug? Lane reversal, usb
> type C and stuff like that need to probe the link in there too.

We already clear it on long hpd.