[Intel-gfx] [PATCH] drm/i915/uncore: Warn on previous unclaimed accesses

[Lucas De Marchi]

Since gen6 we use FPGA_DBG register to detect unclaimed MMIO registers.
This register is in the display engine IP and can only ever detect
unclaimed accesses to registers in this area. However sometimes there
are reports of this triggering for registers in other areas, which
should not be possible.

Right now we always warn after the read/write of registers going through
unclaimed_reg_debug(). However places using __raw_uncore_* may be
triggering the unclaimed access and those being later accounted to a
different register. Let's warn both before and after the read/write
with a slightly different message, so it's clear if the register
reported in the warning is actually the culprit.

Signed-off-by: Lucas De Marchi <lucas.demarchi at intel.com>
---
 drivers/gpu/drm/i915/intel_uncore.c | 29 +++++++++++++++++++++--------
 1 file changed, 21 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
index 8b9caaaacc21..df59ec88459e 100644
--- a/drivers/gpu/drm/i915/intel_uncore.c
+++ b/drivers/gpu/drm/i915/intel_uncore.c
@@ -1502,11 +1502,10 @@ ilk_dummy_write(struct intel_uncore *uncore)
 static void
 __unclaimed_reg_debug(struct intel_uncore *uncore,
 		      const i915_reg_t reg,
-		      const bool read,
-		      const bool before)
+		      const bool read)
 {
 	if (drm_WARN(&uncore->i915->drm,
-		     check_for_unclaimed_mmio(uncore) && !before,
+		     check_for_unclaimed_mmio(uncore),
 		     "Unclaimed %s register 0x%x\n",
 		     read ? "read from" : "write to",
 		     i915_mmio_reg_offset(reg)))
@@ -1514,6 +1513,20 @@ __unclaimed_reg_debug(struct intel_uncore *uncore,
 		uncore->i915->params.mmio_debug--;
 }
 
+static void
+__unclaimed_previous_reg_debug(struct intel_uncore *uncore,
+			       const i915_reg_t reg,
+			       const bool read)
+{
+	if (drm_WARN(&uncore->i915->drm,
+		     check_for_unclaimed_mmio(uncore),
+		     "Unclaimed access detected before %s register 0x%x\n",
+		     read ? "read from" : "write to",
+		     i915_mmio_reg_offset(reg)))
+		/* Only report the first N failures */
+		uncore->i915->params.mmio_debug--;
+}
+
 static inline void
 unclaimed_reg_debug(struct intel_uncore *uncore,
 		    const i915_reg_t reg,
@@ -1526,13 +1539,13 @@ unclaimed_reg_debug(struct intel_uncore *uncore,
 	/* interrupts are disabled and re-enabled around uncore->lock usage */
 	lockdep_assert_held(&uncore->lock);
 
-	if (before)
+	if (before) {
 		spin_lock(&uncore->debug->lock);
-
-	__unclaimed_reg_debug(uncore, reg, read, before);
-
-	if (!before)
+		__unclaimed_previous_reg_debug(uncore, reg, read);
+	} else {
+		__unclaimed_reg_debug(uncore, reg, read);
 		spin_unlock(&uncore->debug->lock);
+	}
 }
 
 #define __vgpu_read(x) \
-- 
2.35.1