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.
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
