Re: [Intel-gfx] [PATCH 3/3] drm/i915: Support DDI lane reversal for DP

From: Sivakumar Thulasimani
Date: Thu Jul 30 2015 - 00:13:47 EST



On 7/29/2015 8:52 PM, Benjamin Tissoires wrote:
On Jul 29 2015 or thereabouts, Sivakumar Thulasimani wrote:
why not detect reverse in intel_dp_detect/intel_hpd_pulse ? that way you can
identify both lane count and reversal state without touching anything in the
link training code. i am yet to upstream my changes for CHT that i can share
if required that does the same in intel_dp_detect without touching any line
in link training path.
With my current limited knowledge of the dp hotplug (and i915 driver) I
am not sure we could detect the reversed state without trying to train 1
lane only. I'd be glad to look at your changes and test them on my
system if you think that could help having a cleaner solution.

Cheers,
Benjamin
No, what i recommended was to do link training but in intel_dp_detect. Since USB Type C cable
also has its own lane count restriction (it can have different lane count than the one supported
by panel) you might have to figure that out as well. so both reversal and lane count detection
can be done outside the modeset path and keep the code free of type C changes outside
detection path.

Please find below the code to do the same. Do not waste time trying to apply this directly on
nightly since this is based on a local tree and because this is pre- atomic changes code, so you
might have to modify chv_upfront_link_train to work on top of the latest nightly code. we
are supposed to upstream this and is in my todo list.

---------------------------------------------------------------------------------------------------------------------------

Author: Durgadoss R <durgadoss.r@xxxxxxxxx>
Date: Fri May 22 14:30:07 2015 +0530

drm/i915: Enable Upfront link training for type-C DP support

To support USB type C alternate DP mode, the display driver needs to know the
number of lanes required by DP panel as well as number of lanes that can be
supported by the type-C cable. Sometimes, the type-C cable may limit the
bandwidth even if Panel can support more lanes. To address these scenarios,
the display driver will start link training with max lanes, and if the link
training fails, the driver then falls back to x2 lanes.

* Since link training is done before modeset, planes are not enabled. Only
encoder and the its associated PLLs are enabled.
* Once link training is done, the encoder and its PLLs are disabled; so that
the subsequent modeset is not aware of these changes.
* As of now, this is tested only on CHV.

Signed-off-by: Durgadoss R <durgadoss.r@xxxxxxxxx>

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 0c8ae2a..c72dcaa 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -14793,3 +14793,121 @@ intel_display_print_error_state(struct drm_i915_error_state_buf *m,
err_printf(m, " VSYNC: %08x\n", error->transcoder[i].vsync);
}
}
+
+bool chv_upfront_link_train(struct drm_device *dev,
+ struct intel_dp *intel_dp, struct intel_crtc *crtc)
+{
+ struct drm_i915_private *dev_priv = dev->dev_private;
+ struct intel_connector *connector = intel_dp->attached_connector;
+ struct intel_encoder *encoder = connector->encoder;
+ bool found = false;
+ bool valid_crtc = false;
+
+ if (!connector || !encoder) {
+ DRM_DEBUG_KMS("dp connector/encoder is NULL\n");
+ return false;
+ }
+
+ /* If we already have a crtc, start link training directly */
+ if (crtc) {
+ valid_crtc = true;
+ goto start_link_train;
+ }
+
+ /* Find an unused crtc and use it for link training */
+ for_each_intel_crtc(dev, crtc) {
+ if (intel_crtc_active(&crtc->base))
+ continue;
+
+ connector->new_encoder = encoder;
+ encoder->new_crtc = crtc;
+ encoder->base.crtc = &crtc->base;
+
+ /* Make sure the new crtc will work with the encoder */
+ if (drm_encoder_crtc_ok(&encoder->base,
+ &crtc->base)) {
+ found = true;
+ break;
+ }
+ }
+
+ if (!found) {
+ DRM_ERROR("Could not find crtc for upfront link training\n");
+ return false;
+ }
+
+start_link_train:
+
+ DRM_DEBUG_KMS("upfront link training on pipe:%c\n",
+ pipe_name(crtc->pipe));
+ found = false;
+
+ /* Initialize with Max Link rate & lane count supported by panel */
+ intel_dp->link_bw = intel_dp->dpcd[DP_MAX_LINK_RATE];
+ intel_dp->lane_count = intel_dp->dpcd[DP_MAX_LANE_COUNT] &
+ DP_MAX_LANE_COUNT_MASK;
+
+ do {
+ /* Find port clock from link_bw */
+ crtc->config.port_clock =
+ drm_dp_bw_code_to_link_rate(intel_dp->link_bw);
+
+ /* Enable PLL followed by port */
+ intel_dp_set_clock(encoder, &crtc->config, intel_dp->link_bw);
+ chv_update_pll(crtc);
+ encoder->pre_pll_enable(encoder);
+ chv_enable_pll(crtc);
+ encoder->pre_enable(encoder);
+
+ /* Check if link training passed; if so update lane count */
+ if (intel_dp->train_set_valid) {
+ intel_dp->dpcd[DP_MAX_LANE_COUNT] &=
+ ~DP_MAX_LANE_COUNT_MASK;
+ intel_dp->dpcd[DP_MAX_LANE_COUNT] |=
+ intel_dp->lane_count & DP_MAX_LANE_COUNT_MASK;
+
+ found = true;
+ }
+
+ /* Reset encoder for next retry or for clean up */
+ encoder->disable(encoder);
+ encoder->post_disable(encoder);
+ chv_disable_pll(dev_priv, crtc->pipe);
+
+ if (found)
+ goto exit;
+
+ DRM_DEBUG_KMS("upfront link training failed. lanes:%d bw:%d\n",
+ intel_dp->lane_count, intel_dp->link_bw);
+
+ /* Go down to the next level and retry link training */
+ if (intel_dp->lane_count == 4) {
+ intel_dp->lane_count = 2;
+ } else if (intel_dp->lane_count == 2) {
+ intel_dp->lane_count = 1;
+ } else if (intel_dp->link_bw == DP_LINK_BW_5_4) {
+ intel_dp->link_bw = DP_LINK_BW_2_7;
+ intel_dp->lane_count = 4;
+ } else if (intel_dp->link_bw == DP_LINK_BW_2_7) {
+ intel_dp->link_bw = DP_LINK_BW_1_62;
+ intel_dp->lane_count = 4;
+ } else {
+ /* Tried all combinations, so exit */
+ break;
+ }
+
+ } while (1);
+
+exit:
+ /* Clear local associations made */
+ if (!valid_crtc) {
+ connector->new_encoder = NULL;
+ encoder->new_crtc = NULL;
+ encoder->base.crtc = NULL;
+ }
+
+ if (found)
+ DRM_DEBUG_KMS("upfront link training passed. lanes:%d bw:%d\n",
+ intel_dp->lane_count, intel_dp->link_bw);
+ return found;
+}
diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 97f03bf..394a7a5 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -878,7 +878,7 @@ intel_dp_connector_unregister(struct intel_connector *intel_connector)
intel_connector_unregister(intel_connector);
}

-static void
+void
intel_dp_set_clock(struct intel_encoder *encoder,
struct intel_crtc_config *pipe_config, int link_bw)
{
@@ -1010,7 +1010,6 @@ intel_dp_compute_config(struct intel_encoder *encoder,
link_clock = drm_dp_bw_code_to_link_rate(bws[clock]);
link_avail = intel_dp_max_data_rate(link_clock,
lane_count);
-
if (mode_rate <= link_avail) {
goto found;
}
@@ -4522,6 +4521,11 @@ g4x_dp_detect(struct intel_dp *intel_dp)
if ((I915_READ(PORT_HOTPLUG_STAT) & bit) == 0)
return connector_status_disconnected;

+ /* Avoid DPCD opertations if status is same */
+ if (intel_dp->attached_connector->base.status ==
+ connector_status_connected)
+ return connector_status_connected;
+
return intel_dp_detect_dpcd(intel_dp);
}

@@ -4566,11 +4570,13 @@ intel_dp_detect(struct drm_connector *connector, bool force)
struct intel_dp *intel_dp = intel_attached_dp(connector);
struct intel_digital_port *intel_dig_port = dp_to_dig_port(intel_dp);
struct intel_encoder *intel_encoder = &intel_dig_port->base;
+ struct drm_crtc *crtc = intel_dig_port->base.base.crtc;
struct drm_device *dev = connector->dev;
struct drm_i915_private *dev_priv = dev->dev_private;
enum drm_connector_status status;
enum intel_display_power_domain power_domain;
struct edid *edid = NULL;
+ struct intel_crtc *intel_crtc = NULL;

intel_runtime_pm_get(dev_priv);

@@ -4590,6 +4596,11 @@ intel_dp_detect(struct drm_connector *connector, bool force)
if (status != connector_status_connected)
goto out;

+ if (connector->status == connector_status_connected) {
+ DRM_DEBUG_KMS("Connector status is already connected\n");
+ goto out;
+ }
+
intel_dp_probe_oui(intel_dp);

if (intel_dp->force_audio != HDMI_AUDIO_AUTO) {
@@ -4604,6 +4615,22 @@ intel_dp_detect(struct drm_connector *connector, bool force)

if (intel_encoder->type != INTEL_OUTPUT_EDP)
intel_encoder->type = INTEL_OUTPUT_DISPLAYPORT;
+
+ if (IS_CHERRYVIEW(dev) &&
+ intel_encoder->type == INTEL_OUTPUT_DISPLAYPORT) {
+ /* Handle connected boot scenario where panel is enabled
+ * by GOP/VBIOS.
+ */
+ if (intel_encoder->connectors_active &&
+ crtc && crtc->enabled) {
+ intel_crtc = to_intel_crtc(crtc);
+ DRM_DEBUG_KMS("Disabling crtc %c for upfront link training\n",
+ pipe_name(intel_crtc->pipe));
+ intel_crtc_control(crtc, false);
+ }
+ chv_upfront_link_train(dev, intel_dp, intel_crtc);
+ }
+
status = connector_status_connected;

out:
diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index fc266da..15eef94d 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -991,6 +991,10 @@ void intel_dp_start_link_train(struct intel_dp *intel_dp);
void intel_dp_complete_link_train(struct intel_dp *intel_dp);
void intel_dp_stop_link_train(struct intel_dp *intel_dp);
bool intel_dp_fast_link_train(struct intel_dp *intel_dp);
+bool chv_upfront_link_train(struct drm_device *dev,
+ struct intel_dp *intel_dp, struct intel_crtc *crtc);
+void intel_dp_set_clock(struct intel_encoder *encoder,
+ struct intel_crtc_config *pipe_config, int link_bw);
void intel_dp_sink_dpms(struct intel_dp *intel_dp, int mode);
void intel_dp_set_m2_n2(struct intel_crtc *crtc, struct intel_link_m_n *m_n);
void intel_dp_encoder_destroy(struct drm_encoder *encoder);

--
regards,
Sivakumar

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