On Mon, Apr 04, 2022 at 01:38:58PM -0700, Matt Roper wrote:
On Mon, Apr 04, 2022 at 11:18:44AM -0700, Lucas De Marchi wrote:
Sine 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.
This keeps track of the last 4 registers which should hopefully be
sufficient to understand where these are coming from. And without
increasing the debug struct too much:
Doesn't the unclaimed access checking happen within uncore->lock,
guaranteeing that an unclaimed access triggered by an uncore read/write
is always from the current one and not a previous one? Presumably if
the wrong access is being identified, then the true culprit is probably
a __raw_uncore_{read,write} that doesn't have any checking of its own
and doesn't use the uncore lock? I think we could probably confirm this
theory by updating __unclaimed_reg_debug() to drop the "!before"
condition and print a slightly different message if we detect an
unclaimed access has already happened before we do the new operation.
I was actually thinking this could come from the 2 mmio reads being
batched and the hw not updating the FPGA_DBG in between.
__raw_uncore_* being used could be true.... from what I can see we'd
need to check users of intel_de_read_fw().
Lucas De Marchi
Matt
Before:
struct intel_uncore_mmio_debug {
spinlock_t lock; /* 0 64 */
/* --- cacheline 1 boundary (64 bytes) --- */
int unclaimed_mmio_check; /* 64 4 */
int saved_mmio_check; /* 68 4 */
u32 suspend_count; /* 72 4 */
/* size: 80, cachelines: 2, members: 4 */
/* padding: 4 */
/* last cacheline: 16 bytes */
};
After:
struct intel_uncore_mmio_debug {
spinlock_t lock; /* 0 64 */
/* --- cacheline 1 boundary (64 bytes) --- */
int unclaimed_mmio_check; /* 64 4 */
int saved_mmio_check; /* 68 4 */
u32 last_reg[4]; /* 72 16 */
u32 last_reg_pos; /* 88 4 */
u32 suspend_count; /* 92 4 */
/* size: 96, cachelines: 2, members: 6 */
/* last cacheline: 32 bytes */
};
Signed-off-by: Lucas De Marchi <lucas.demarchi@xxxxxxxxx>
---
drivers/gpu/drm/i915/intel_uncore.c | 18 +++++++++++++++++-
drivers/gpu/drm/i915/intel_uncore.h | 4 ++++
2 files changed, 21 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
index 8b9caaaacc21..31a23b0e2907 100644
--- a/drivers/gpu/drm/i915/intel_uncore.c
+++ b/drivers/gpu/drm/i915/intel_uncore.c
@@ -1509,9 +1509,25 @@ __unclaimed_reg_debug(struct intel_uncore *uncore,
check_for_unclaimed_mmio(uncore) && !before,
"Unclaimed %s register 0x%x\n",
read ? "read from" : "write to",
- i915_mmio_reg_offset(reg)))
+ i915_mmio_reg_offset(reg))) {
+ unsigned int i;
+
/* Only report the first N failures */
uncore->i915->params.mmio_debug--;
+
+ drm_dbg(&uncore->i915->drm, "Last register accesses:\n");
+ for (i = uncore->debug->last_reg_pos;
+ i < uncore->debug->last_reg_pos + INTEL_UNCORE_MMIO_DEBUG_REG_COUNT;
+ i++)
+ drm_dbg(&uncore->i915->drm, "0x%x\n",
+ uncore->debug->last_reg[i % INTEL_UNCORE_MMIO_DEBUG_REG_COUNT]);
+ }
+
+ if (!before) {
+ uncore->debug->last_reg[uncore->debug->last_reg_pos++] =
+ i915_mmio_reg_offset(reg);
+ uncore->debug->last_reg_pos %= INTEL_UNCORE_MMIO_DEBUG_REG_COUNT;
+ }
}
static inline void
diff --git a/drivers/gpu/drm/i915/intel_uncore.h b/drivers/gpu/drm/i915/intel_uncore.h
index 52fe3d89dd2b..5b5d2858ae11 100644
--- a/drivers/gpu/drm/i915/intel_uncore.h
+++ b/drivers/gpu/drm/i915/intel_uncore.h
@@ -38,10 +38,14 @@ struct intel_runtime_pm;
struct intel_uncore;
struct intel_gt;
+#define INTEL_UNCORE_MMIO_DEBUG_REG_COUNT 4
+
struct intel_uncore_mmio_debug {
spinlock_t lock; /** lock is also taken in irq contexts. */
int unclaimed_mmio_check;
int saved_mmio_check;
+ u32 last_reg[INTEL_UNCORE_MMIO_DEBUG_REG_COUNT];
+ u32 last_reg_pos;
u32 suspend_count;
};
--
2.35.1
--
Matt Roper
Graphics Software Engineer
VTT-OSGC Platform Enablement
Intel Corporation
(916) 356-2795
