[PATCH 1/4] drm/i915: Disable preemption and sleeping while using the punit sideband

[Chris Wilson]

While we talk to the punit over its sideband, we need to prevent the cpu
from sleeping in order to prevent a potential machine hang.

Note that by itself, it appears that pm_qos_update_request (via
intel_idle) doesn't provide a sufficient barrier to ensure that all core
are indeed awake (out of Cstate) and that the package is awake. To do so,
we need to supplement the pm_qos with a manual ping on_each_cpu.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=109051
References: https://bugs.freedesktop.org/show_bug.cgi?id=102657
References: https://bugzilla.kernel.org/show_bug.cgi?id=195255
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala at linux.intel.com>
Cc: Hans de Goede <hdegoede at redhat.com>
---
 drivers/gpu/drm/i915/i915_drv.c       |  6 ++++
 drivers/gpu/drm/i915/i915_drv.h       |  1 +
 drivers/gpu/drm/i915/intel_sideband.c | 61 ++++++++++++++++++++++++-----------
 3 files changed, 50 insertions(+), 18 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
index 6c8da9d20c33..d4b90cc0130b 100644
--- a/drivers/gpu/drm/i915/i915_drv.c
+++ b/drivers/gpu/drm/i915/i915_drv.c
@@ -902,6 +902,9 @@ static int i915_driver_init_early(struct drm_i915_private *dev_priv,
 	spin_lock_init(&dev_priv->uncore.lock);
 
 	mutex_init(&dev_priv->sb_lock);
+	pm_qos_add_request(&dev_priv->sb_qos,
+			   PM_QOS_CPU_DMA_LATENCY, PM_QOS_DEFAULT_VALUE);
+
 	mutex_init(&dev_priv->modeset_restore_lock);
 	mutex_init(&dev_priv->av_mutex);
 	mutex_init(&dev_priv->wm.wm_mutex);
@@ -953,6 +956,9 @@ static void i915_driver_cleanup_early(struct drm_i915_private *dev_priv)
 	intel_irq_fini(dev_priv);
 	i915_workqueues_cleanup(dev_priv);
 	i915_engines_cleanup(dev_priv);
+
+	pm_qos_remove_request(&dev_priv->sb_qos);
+	mutex_destroy(&dev_priv->sb_lock);
 }
 
 static int i915_mmio_setup(struct drm_i915_private *dev_priv)
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index a689396d0ff6..ff3f9effc0bb 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -1887,6 +1887,7 @@ struct drm_i915_private {
 
 	/* Sideband mailbox protection */
 	struct mutex sb_lock;
+	struct pm_qos_request sb_qos;
 
 	/** Cached value of IMR to avoid reads in updating the bitfield */
 	union {
diff --git a/drivers/gpu/drm/i915/intel_sideband.c b/drivers/gpu/drm/i915/intel_sideband.c
index 75c872bb8cc9..02bdd2e2cef6 100644
--- a/drivers/gpu/drm/i915/intel_sideband.c
+++ b/drivers/gpu/drm/i915/intel_sideband.c
@@ -22,6 +22,8 @@
  *
  */
 
+#include <asm/iosf_mbi.h>
+
 #include "i915_drv.h"
 #include "intel_drv.h"
 
@@ -39,18 +41,20 @@
 /* Private register write, double-word addressing, non-posted */
 #define SB_CRWRDA_NP	0x07
 
-static int vlv_sideband_rw(struct drm_i915_private *dev_priv, u32 devfn,
-			   u32 port, u32 opcode, u32 addr, u32 *val)
+static void ping(void *info)
 {
-	u32 cmd, be = 0xf, bar = 0;
-	bool is_read = (opcode == SB_MRD_NP || opcode == SB_CRRDDA_NP);
+}
 
-	cmd = (devfn << IOSF_DEVFN_SHIFT) | (opcode << IOSF_OPCODE_SHIFT) |
-		(port << IOSF_PORT_SHIFT) | (be << IOSF_BYTE_ENABLES_SHIFT) |
-		(bar << IOSF_BAR_SHIFT);
+static int vlv_sideband_rw(struct drm_i915_private *dev_priv,
+			   u32 devfn, u32 port, u32 opcode,
+			   u32 addr, u32 *val)
+{
+	const bool is_read = (opcode == SB_MRD_NP || opcode == SB_CRRDDA_NP);
+	int err;
 
-	WARN_ON(!mutex_is_locked(&dev_priv->sb_lock));
+	lockdep_assert_held(&dev_priv->sb_lock);
 
+	/* Flush the previous comms, just in case it failed last time. */
 	if (intel_wait_for_register(dev_priv,
 				    VLV_IOSF_DOORBELL_REQ, IOSF_SB_BUSY, 0,
 				    5)) {
@@ -59,22 +63,43 @@ static int vlv_sideband_rw(struct drm_i915_private *dev_priv, u32 devfn,
 		return -EAGAIN;
 	}
 
-	I915_WRITE(VLV_IOSF_ADDR, addr);
-	I915_WRITE(VLV_IOSF_DATA, is_read ? 0 : *val);
-	I915_WRITE(VLV_IOSF_DOORBELL_REQ, cmd);
+	iosf_mbi_punit_acquire();
 
-	if (intel_wait_for_register(dev_priv,
-				    VLV_IOSF_DOORBELL_REQ, IOSF_SB_BUSY, 0,
-				    5)) {
+	/*
+	 * Prevent the cpu from sleeping while we use this sideband, otherwise
+	 * the punit may cause a machine hang.
+	 */
+	pm_qos_update_request(&dev_priv->sb_qos, 0);
+	on_each_cpu(ping, NULL, 1);
+	preempt_disable();
+
+	I915_WRITE_FW(VLV_IOSF_ADDR, addr);
+	I915_WRITE_FW(VLV_IOSF_DATA, is_read ? 0 : *val);
+	I915_WRITE_FW(VLV_IOSF_DOORBELL_REQ,
+		      (devfn << IOSF_DEVFN_SHIFT) |
+		      (opcode << IOSF_OPCODE_SHIFT) |
+		      (port << IOSF_PORT_SHIFT) |
+		      (0xf << IOSF_BYTE_ENABLES_SHIFT) |
+		      (0 << IOSF_BAR_SHIFT) |
+		      IOSF_SB_BUSY);
+
+	if (__intel_wait_for_register_fw(dev_priv,
+					 VLV_IOSF_DOORBELL_REQ, IOSF_SB_BUSY, 0,
+					 10000, 0, NULL) == 0) {
+		if (is_read)
+			*val = I915_READ_FW(VLV_IOSF_DATA);
+		err = 0;
+	} else {
 		DRM_DEBUG_DRIVER("IOSF sideband finish wait (%s) timed out\n",
 				 is_read ? "read" : "write");
-		return -ETIMEDOUT;
+		err = -ETIMEDOUT;
 	}
 
-	if (is_read)
-		*val = I915_READ(VLV_IOSF_DATA);
+	preempt_enable();
+	pm_qos_update_request(&dev_priv->sb_qos, PM_QOS_DEFAULT_VALUE);
+	iosf_mbi_punit_release();
 
-	return 0;
+	return err;
 }
 
 u32 vlv_punit_read(struct drm_i915_private *dev_priv, u32 addr)
-- 
2.15.1