[PATCH v4 1/3] drm/panthor: Add tracepoint for cache flushing

[Nicolas Frattaroli]

Add a new event tracepoint: gpu_cache_flush to be emitted after a GPU
cache flush completes, with duration and return status arguments.

This allows debugging the duration a flush takes irrespective of initial
function entry lock contention, and communicates information about
whether the flush timed out or errored out in other ways, and which
caches were flushed.

Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@xxxxxxxxxxxxx>
---
 drivers/gpu/drm/panthor/panthor_gpu.c   | 26 +++++++++++++++++++++-
 drivers/gpu/drm/panthor/panthor_trace.h | 38 +++++++++++++++++++++++++++++++++
 2 files changed, 63 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/panthor/panthor_gpu.c b/drivers/gpu/drm/panthor/panthor_gpu.c
index c013d6bf9a59..7088371c6d64 100644
--- a/drivers/gpu/drm/panthor/panthor_gpu.c
+++ b/drivers/gpu/drm/panthor/panthor_gpu.c
@@ -317,6 +317,21 @@ int panthor_gpu_l2_power_on(struct panthor_device *ptdev)
 	return panthor_gpu_power_on(ptdev, L2, 1, 20000);
 }
 
+static inline void panthor_gpu_emit_flush_caches_tp(struct panthor_device *ptdev,
+						    u64 start, u32 l2, u32 lsc,
+						    u32 other, int ret)
+{
+	u32 duration;
+
+	if (!tracepoint_enabled(gpu_cache_flush) || !start)
+		return;
+
+	if (check_sub_overflow(ktime_get_ns(), start, &duration))
+		duration = U32_MAX;
+
+	trace_gpu_cache_flush(ptdev->base.dev, l2, lsc, other, duration, ret);
+}
+
 /**
  * panthor_gpu_flush_caches() - Flush caches
  * @ptdev: Device.
@@ -331,12 +346,17 @@ int panthor_gpu_flush_caches(struct panthor_device *ptdev,
 {
 	struct panthor_gpu *gpu = ptdev->gpu;
 	unsigned long flags;
+	u64 start = 0;
 	int ret = 0;
 
 	/* Serialize cache flush operations. */
 	guard(mutex)(&ptdev->gpu->cache_flush_lock);
 
 	spin_lock_irqsave(&ptdev->gpu->reqs_lock, flags);
+
+	if (tracepoint_enabled(gpu_cache_flush))
+		start = ktime_get_ns();
+
 	if (!(ptdev->gpu->pending_reqs & GPU_IRQ_CLEAN_CACHES_COMPLETED)) {
 		ptdev->gpu->pending_reqs |= GPU_IRQ_CLEAN_CACHES_COMPLETED;
 		gpu_write(gpu->iomem, GPU_CMD, GPU_FLUSH_CACHES(l2, lsc, other));
@@ -345,8 +365,10 @@ int panthor_gpu_flush_caches(struct panthor_device *ptdev,
 	}
 	spin_unlock_irqrestore(&ptdev->gpu->reqs_lock, flags);
 
-	if (ret)
+	if (ret) {
+		panthor_gpu_emit_flush_caches_tp(ptdev, start, l2, lsc, other, ret);
 		return ret;
+	}
 
 	if (!wait_event_timeout(ptdev->gpu->reqs_acked,
 				!(ptdev->gpu->pending_reqs & GPU_IRQ_CLEAN_CACHES_COMPLETED),
@@ -360,6 +382,8 @@ int panthor_gpu_flush_caches(struct panthor_device *ptdev,
 		spin_unlock_irqrestore(&ptdev->gpu->reqs_lock, flags);
 	}
 
+	panthor_gpu_emit_flush_caches_tp(ptdev, start, l2, lsc, other, ret);
+
 	if (ret) {
 		panthor_device_schedule_reset(ptdev);
 		drm_err(&ptdev->base, "Flush caches timeout");
diff --git a/drivers/gpu/drm/panthor/panthor_trace.h b/drivers/gpu/drm/panthor/panthor_trace.h
index 6ffeb4fe6599..bd8652549ab4 100644
--- a/drivers/gpu/drm/panthor/panthor_trace.h
+++ b/drivers/gpu/drm/panthor/panthor_trace.h
@@ -76,6 +76,44 @@ TRACE_EVENT(gpu_job_irq,
 		  __entry->events, __entry->duration_ns)
 );
 
+/**
+ * gpu_cache_flush - emitted after cache flush completes
+ * @dev: pointer to the &struct device, for printing the device name
+ * @l2: "l2" flush flags
+ * @lsc: "lsc" flush flags
+ * @other: "other" flush flags
+ * @duration_ns: how long the cache flush operation took, in nanoseconds
+ * @ret: return status, 0 == success, negative errno on error
+ *
+ * Begins measuring after any initial lock contention around the locks needed
+ * for flushing caches, but before the actual cache flush is requested. Stops
+ * measuring and is emitted after flush operation is over.
+ */
+TRACE_EVENT(gpu_cache_flush,
+	    TP_PROTO(const struct device *dev, u32 l2, u32 lsc, u32 other,
+		     u32 duration_ns, int ret),
+	    TP_ARGS(dev, l2, lsc, other, duration_ns, ret),
+	    TP_STRUCT__entry(
+		    __string(dev_name, dev_name(dev))
+		    __field(u32, l2)
+		    __field(u32, lsc)
+		    __field(u32, other)
+		    __field(u32, duration_ns)
+		    __field(int, ret)
+	    ),
+	    TP_fast_assign(
+		    __assign_str(dev_name);
+		    __entry->l2          = l2;
+		    __entry->lsc         = lsc;
+		    __entry->other       = other;
+		    __entry->duration_ns = duration_ns;
+		    __entry->ret         = ret;
+	    ),
+	    TP_printk("%s: l2=0x%x lsc=0x%x other=0x%x duration_ns=%u ret=%d",
+		      __get_str(dev_name), __entry->l2, __entry->lsc,
+		      __entry->other, __entry->duration_ns, __entry->ret)
+);
+
 #endif /* __PANTHOR_TRACE_H__ */
 
 #undef TRACE_INCLUDE_PATH

-- 
2.55.0