[Intel-gfx] [PATCH v4 1/1] drm/i915/skl+: Add and enable DP AUX CH mutex

[José Roberto de Souza]

When PSR/PSR2/GTC is enabled hardware can do AUX transactions by it
self, so lets use the mutex register that is available in gen9+ to
avoid concurrent access by hardware and driver.
Older gen handling will be done separated.

Reference: https://01.org/sites/default/files/documentation/intel-gfx-prm-osrc-skl-vol12-display.pdf
Page 198 - AUX programming sequence

Cc: Rodrigo Vivi <rodrigo.vivi at intel.com>
Cc: Jani Nikula <jani.nikula at linux.intel.com>
Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan at intel.com>
Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
Signed-off-by: José Roberto de Souza <jose.souza at intel.com>
---
 drivers/gpu/drm/i915/i915_reg.h |  9 ++++++++
 drivers/gpu/drm/i915/intel_dp.c | 47 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 56 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index eea5b2c537d4..f36e839b4b4f 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -5385,6 +5385,15 @@ enum {
 #define   DP_AUX_CH_CTL_FW_SYNC_PULSE_SKL(c) (((c) - 1) << 5)
 #define   DP_AUX_CH_CTL_SYNC_PULSE_SKL(c)   ((c) - 1)
 
+#define _DPA_AUX_CH_MUTEX	(dev_priv->info.display_mmio_offset + 0x6402C)
+#define _DPB_AUX_CH_MUTEX	(dev_priv->info.display_mmio_offset + 0x6412C)
+#define _DPC_AUX_CH_MUTEX	(dev_priv->info.display_mmio_offset + 0x6422C)
+#define _DPD_AUX_CH_MUTEX	(dev_priv->info.display_mmio_offset + 0x6432C)
+#define _DPF_AUX_CH_MUTEX	(dev_priv->info.display_mmio_offset + 0x6452C)
+#define DP_AUX_CH_MUTEX(port)	_MMIO_PORT(port, _DPA_AUX_CH_MUTEX, _DPB_AUX_CH_MUTEX)
+#define   DP_AUX_CH_MUTEX_ENABLE		(1 << 31)
+#define   DP_AUX_CH_MUTEX_STATUS		(1 << 30)
+
 /*
  * Computing GMCH M and N values for the Display Port link
  *
diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 2c3eb90b9499..7004239e4c9e 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -1081,6 +1081,42 @@ static uint32_t intel_dp_get_aux_send_ctl(struct intel_dp *intel_dp,
 						aux_clock_divider);
 }
 
+static bool intel_dp_aux_ch_trylock(struct intel_dp *intel_dp)
+{
+	struct intel_digital_port *intel_dig_port = dp_to_dig_port(intel_dp);
+	struct drm_i915_private *dev_priv =
+			to_i915(intel_dig_port->base.base.dev);
+
+	if (INTEL_GEN(dev_priv) < 9)
+		return true;
+
+	/* Spec says that mutex is acquired when status bit is read as unset,
+	 * here waiting for 2msec(+-4 aux transactions) before give up.
+	 */
+	if (intel_wait_for_register(dev_priv, DP_AUX_CH_MUTEX(intel_dp->aux_ch),
+				    DP_AUX_CH_MUTEX_STATUS, 0, 2)) {
+		DRM_DEBUG_KMS("aux channel %c locked for 2msec, timing out\n",
+			      aux_ch_name(intel_dp->aux_ch));
+		return false;
+	}
+
+	return true;
+}
+
+static void intel_dp_aux_ch_unlock(struct intel_dp *intel_dp)
+{
+	struct intel_digital_port *intel_dig_port = dp_to_dig_port(intel_dp);
+	struct drm_i915_private *dev_priv =
+			to_i915(intel_dig_port->base.base.dev);
+
+	if (INTEL_GEN(dev_priv) < 9)
+		return;
+
+	/* set the status bit releases the mutex + keeping mutex enabled */
+	I915_WRITE(DP_AUX_CH_MUTEX(intel_dp->aux_ch),
+		   DP_AUX_CH_MUTEX_ENABLE | DP_AUX_CH_MUTEX_STATUS);
+}
+
 static int
 intel_dp_aux_ch(struct intel_dp *intel_dp,
 		const uint8_t *send, int send_bytes,
@@ -1119,6 +1155,11 @@ intel_dp_aux_ch(struct intel_dp *intel_dp,
 
 	intel_dp_check_edp(intel_dp);
 
+	if (!intel_dp_aux_ch_trylock(intel_dp)) {
+		ret = -EBUSY;
+		goto out_locked;
+	}
+
 	/* Try to wait for any previous AUX channel activity */
 	for (try = 0; try < 3; try++) {
 		status = I915_READ_NOTRACE(ch_ctl);
@@ -1248,6 +1289,8 @@ intel_dp_aux_ch(struct intel_dp *intel_dp,
 
 	ret = recv_bytes;
 out:
+	intel_dp_aux_ch_unlock(intel_dp);
+out_locked:
 	pm_qos_update_request(&dev_priv->pm_qos, PM_QOS_DEFAULT_VALUE);
 
 	if (vdd)
@@ -1544,6 +1587,10 @@ intel_dp_aux_init(struct intel_dp *intel_dp)
 	else
 		intel_dp->get_aux_send_ctl = g4x_get_aux_send_ctl;
 
+	if (INTEL_GEN(dev_priv) >= 9)
+		I915_WRITE(DP_AUX_CH_MUTEX(intel_dp->aux_ch),
+			   DP_AUX_CH_MUTEX_ENABLE);
+
 	drm_dp_aux_init(&intel_dp->aux);
 
 	/* Failure to allocate our preferred name is not critical */
-- 
2.16.2