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: Dhinakaran Pandiyan <dhinakaran.pandi...@intel.com>
Cc: Rodrigo Vivi <rodrigo.v...@intel.com>
Cc: Jani Nikula <jani.nik...@linux.intel.com>
Cc: Ville Syrjälä <ville.syrj...@linux.intel.com>
Signed-off-by: José Roberto de Souza <jose.so...@intel.com>
---

Changelog:
v2
- removed the PSR dependency, now getting lock all the times when available
- renamed functions to avoid nested calls
- moved register bits right after the DP_AUX_CH_MUTEX()
- removed 'drm/i915: keep AUX powered while PSR is enabled' Dhinakaran Pandiyan 
will sent a better and final version
v3
- rebased on top of Ville's AUX series
- moved port registers to above DP_AUX_CH_MUTEX()
- using intel_wait_for_register() instead of the internal version
v4
- removed virtual function to get mutex register address
- enabling the mutex back only on aux channel init
- added the aux channel name to the timeout debug message
v5
- renamed DP_AUX_CH_MUTEX() parameter to aux_ch
- renamed goto label when intel_dp_aux_ch_trylock() fails
v6
- enabling mutex in the first trylock to cover all power management cases
- saving and restoring reserved bits in the mutex register

 drivers/gpu/drm/i915/i915_reg.h |  9 +++++++
 drivers/gpu/drm/i915/intel_dp.c | 58 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 67 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index 258e86eb37d5..da1dcef24ebf 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -5388,6 +5388,15 @@ 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(aux_ch)        _MMIO_PORT(aux_ch, _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 c722a6750e90..b8ff5fa41b71 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -1065,6 +1065,57 @@ static uint32_t skl_get_aux_send_ctl(struct intel_dp 
*intel_dp,
               DP_AUX_CH_CTL_SYNC_PULSE_SKL(32);
 }
 
+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);
+       u32 val;
+
+       if (INTEL_GEN(dev_priv) < 9)
+               return true;
+
+       /* A read to mutex register will request the lock if mutex is enabled */
+       val = I915_READ(DP_AUX_CH_MUTEX(intel_dp->aux_ch));
+       if ((val & DP_AUX_CH_MUTEX_ENABLE) == 0) {
+               /* Mutex is disabled, enables it */
+               I915_WRITE(DP_AUX_CH_MUTEX(intel_dp->aux_ch),
+                          val | DP_AUX_CH_MUTEX_ENABLE);
+               /* Now that the mutex is enabled, request the lock */
+               val = I915_READ(DP_AUX_CH_MUTEX(intel_dp->aux_ch));
+       }
+
+       /* Lock is acquired when status bit is unset */
+       if ((val & DP_AUX_CH_MUTEX_STATUS) == 0)
+               return true;
+
+       /* Try to get the lock 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);
+       u32 val;
+
+       if (INTEL_GEN(dev_priv) < 9)
+               return;
+
+       /* Set the status bit releases the mutex */
+       val = I915_READ(DP_AUX_CH_MUTEX(intel_dp->aux_ch));
+       val |= DP_AUX_CH_MUTEX_STATUS;
+       I915_WRITE(DP_AUX_CH_MUTEX(intel_dp->aux_ch), val);
+}
+
 static int
 intel_dp_aux_xfer(struct intel_dp *intel_dp,
                  const uint8_t *send, int send_bytes,
@@ -1104,6 +1155,11 @@ intel_dp_aux_xfer(struct intel_dp *intel_dp,
 
        intel_dp_check_edp(intel_dp);
 
+       if (!intel_dp_aux_ch_trylock(intel_dp)) {
+               ret = -EBUSY;
+               goto out_aux_ch_unlocked;
+       }
+
        /* Try to wait for any previous AUX channel activity */
        for (try = 0; try < 3; try++) {
                status = I915_READ_NOTRACE(ch_ctl);
@@ -1226,6 +1282,8 @@ intel_dp_aux_xfer(struct intel_dp *intel_dp,
 
        ret = recv_bytes;
 out:
+       intel_dp_aux_ch_unlock(intel_dp);
+out_aux_ch_unlocked:
        pm_qos_update_request(&dev_priv->pm_qos, PM_QOS_DEFAULT_VALUE);
 
        if (vdd)
-- 
2.16.2

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