[Intel-gfx] [PATCH v5] drm/i915: handle uncore spinlock when not available

[Luca Coelho]

The uncore code may not always be available (e.g. when we build the
display code with Xe), so we can't always rely on having the uncore's
spinlock.

To handle this, split the spin_lock/unlock_irqsave/restore() into
spin_lock/unlock() followed by a call to local_irq_save/restore() and
create wrapper functions for locking and unlocking the uncore's
spinlock.  In these functions, we have a condition check and only
actually try to lock/unlock the spinlock when I915 is defined, and
thus uncore is available.

This keeps the ifdefs contained in these new functions and all such
logic inside the display code.

Cc: Tvrtko Ursulin <tvrto.ursulin at intel.com>
Cc: Jani Nikula <jani.nikula at intel.com>
Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi at intel.com>
Signed-off-by: Luca Coelho <luciano.coelho at intel.com>
---

In v2:

   * Renamed uncore_spin_*() to intel_spin_*()
   * Corrected the order: save, lock, unlock, restore

In v3:

   * Undid the change to pass drm_i915_private instead of the lock
     itself, since we would have to include i915_drv.h and that pulls
     in a truckload of other includes.

In v4:

   * After a brief attempt to replace this with a different patch,
     we're back to this one;
   * Pass drm_i195_private again, and move the functions to
     intel_vblank.c, so we don't need to include i915_drv.h in a
     header file and it's already included in intel_vblank.c;

In v5:

   * Remove stray include in intel_display.h;
   * Remove unnecessary inline modifiers in the new functions.

drivers/gpu/drm/i915/display/intel_vblank.c | 49 ++++++++++++++++-----
 1 file changed, 39 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_vblank.c b/drivers/gpu/drm/i915/display/intel_vblank.c
index 2cec2abf9746..221fcd6bf77b 100644
--- a/drivers/gpu/drm/i915/display/intel_vblank.c
+++ b/drivers/gpu/drm/i915/display/intel_vblank.c
@@ -265,6 +265,30 @@ int intel_crtc_scanline_to_hw(struct intel_crtc *crtc, int scanline)
 	return (scanline + vtotal - crtc->scanline_offset) % vtotal;
 }
 
+/*
+ * The uncore version of the spin lock functions is used to decide
+ * whether we need to lock the uncore lock or not.  This is only
+ * needed in i915, not in Xe.
+ *
+ * This lock in i915 is needed because some old platforms (at least
+ * IVB and possibly HSW as well), which are not supported in Xe, need
+ * all register accesses to the same cacheline to be serialized,
+ * otherwise they may hang.
+ */
+static void intel_vblank_section_enter(struct drm_i915_private *i915)
+{
+#ifdef I915
+	spin_lock(&i915->uncore.lock);
+#endif
+}
+
+static void intel_vblank_section_exit(struct drm_i915_private *i915)
+{
+#ifdef I915
+	spin_unlock(&i915->uncore.lock);
+#endif
+}
+
 static bool i915_get_crtc_scanoutpos(struct drm_crtc *_crtc,
 				     bool in_vblank_irq,
 				     int *vpos, int *hpos,
@@ -302,11 +326,12 @@ static bool i915_get_crtc_scanoutpos(struct drm_crtc *_crtc,
 	}
 
 	/*
-	 * Lock uncore.lock, as we will do multiple timing critical raw
-	 * register reads, potentially with preemption disabled, so the
-	 * following code must not block on uncore.lock.
+	 * Enter vblank critical section, as we will do multiple
+	 * timing critical raw register reads, potentially with
+	 * preemption disabled, so the following code must not block.
 	 */
-	spin_lock_irqsave(&dev_priv->uncore.lock, irqflags);
+	local_irq_save(irqflags);
+	intel_vblank_section_enter(dev_priv);
 
 	/* preempt_disable_rt() should go right here in PREEMPT_RT patchset. */
 
@@ -374,7 +399,8 @@ static bool i915_get_crtc_scanoutpos(struct drm_crtc *_crtc,
 
 	/* preempt_enable_rt() should go right here in PREEMPT_RT patchset. */
 
-	spin_unlock_irqrestore(&dev_priv->uncore.lock, irqflags);
+	intel_vblank_section_exit(dev_priv);
+	local_irq_restore(irqflags);
 
 	/*
 	 * While in vblank, position will be negative
@@ -412,9 +438,13 @@ int intel_get_crtc_scanline(struct intel_crtc *crtc)
 	unsigned long irqflags;
 	int position;
 
-	spin_lock_irqsave(&dev_priv->uncore.lock, irqflags);
+	local_irq_save(irqflags);
+	intel_vblank_section_enter(dev_priv);
+
 	position = __intel_get_crtc_scanline(crtc);
-	spin_unlock_irqrestore(&dev_priv->uncore.lock, irqflags);
+
+	intel_vblank_section_exit(dev_priv);
+	local_irq_restore(irqflags);
 
 	return position;
 }
@@ -537,7 +567,7 @@ void intel_crtc_update_active_timings(const struct intel_crtc_state *crtc_state,
 	 * Need to audit everything to make sure it's safe.
 	 */
 	spin_lock_irqsave(&i915->drm.vblank_time_lock, irqflags);
-	spin_lock(&i915->uncore.lock);
+	intel_vblank_section_enter(i915);
 
 	drm_calc_timestamping_constants(&crtc->base, &adjusted_mode);
 
@@ -546,7 +576,6 @@ void intel_crtc_update_active_timings(const struct intel_crtc_state *crtc_state,
 	crtc->mode_flags = mode_flags;
 
 	crtc->scanline_offset = intel_crtc_scanline_offset(crtc_state);
-
-	spin_unlock(&i915->uncore.lock);
+	intel_vblank_section_exit(i915);
 	spin_unlock_irqrestore(&i915->drm.vblank_time_lock, irqflags);
 }
-- 
2.39.2