[PATCH v2 21/23] coresight: trbe: Read TRBSR after prohibiting and flushing trace

[Leo Yan <leo.yan@arm.com>]

The IRQ handler needs a stable TRBSR_EL1 value before classifying the
interrupt. If the PE can still generate trace, or if pending trace has
not been flushed, TRBSR can still change while the handler is sampling
it. This is especially important for TRBSR.S bit, which is used to
decide whether the TRBE has stopped.

Move the drain buffer into arm_trbe_prohibit_trace(), so the handler
first prohibits trace and flushes trace before reading TRBSR_EL1. Once
this has been done, the IRQ path no longer needs the unconditional
trbe_drain_and_disable_local(); it only needs to disable TRBE before
handling the stopped-buffer status.

Refactor the IRQ exit path accordingly: restore TRFCR on non-truncated
exits, while the truncated path still runs the perf IRQ work to shut
down the event.

Signed-off-by: Leo Yan <leo.yan@arm.com>
---
 drivers/hwtracing/coresight/coresight-trbe.c | 40 +++++++++++++++++++---------
 1 file changed, 28 insertions(+), 12 deletions(-)

diff --git a/drivers/hwtracing/coresight/coresight-trbe.c b/drivers/hwtracing/coresight/coresight-trbe.c
index c83c440d4ac13c346bc2a7f9093951c186c90157..36f143a15e680b28aa6ca6a43ad7d3ee134693be 100644
--- a/drivers/hwtracing/coresight/coresight-trbe.c
+++ b/drivers/hwtracing/coresight/coresight-trbe.c
@@ -1207,24 +1207,34 @@ static bool is_perf_trbe(struct perf_output_handle *handle)
 	return true;
 }
 
-static u64 cpu_prohibit_trace(void)
+static u64 arm_trbe_prohibit_trace(void)
 {
 	u64 trfcr = read_trfcr();
 
 	/* Prohibit tracing at EL0 & the kernel EL */
 	write_trfcr(trfcr & ~(TRFCR_EL1_ExTRE | TRFCR_EL1_E0TRE));
+
+	/* Ensure the program-flow trace is flushed */
+	trbe_drain_buffer();
+
 	/* Return the original value of the TRFCR */
 	return trfcr;
 }
 
+static void arm_trbe_allow_trace(u64 trfcr)
+{
+	/* Allow tracing at EL0 & the kernel EL */
+	write_trfcr(trfcr);
+}
+
 static irqreturn_t arm_trbe_irq_handler(int irq, void *dev)
 {
 	struct trbe_cpudata *cpudata = dev;
 	struct perf_output_handle *handle = cpudata->handle;
 	enum trbe_fault_action act;
-	u64 status;
 	bool truncated = false;
-	u64 trfcr;
+	u64 status, trfcr;
+	irqreturn_t ret;
 
 	if (!handle || !perf_get_aux(handle))
 		return IRQ_NONE;
@@ -1232,22 +1242,25 @@ static irqreturn_t arm_trbe_irq_handler(int irq, void *dev)
 	if (!is_perf_trbe(handle))
 		return IRQ_NONE;
 
+	/* Prohibit the CPU from tracing before we disable the TRBE */
+	trfcr = arm_trbe_prohibit_trace();
+
 	/* Reads to TRBSR_EL1 is fine when TRBE is active */
 	status = read_sysreg_s(SYS_TRBSR_EL1);
 	/*
 	 * If the pending IRQ was handled by update_buffer callback
 	 * we have nothing to do here.
 	 */
-	if (!is_trbe_irq(status))
-		return IRQ_NONE;
+	if (!is_trbe_irq(status)) {
+		ret = IRQ_NONE;
+		goto out;
+	}
 
-	/* Prohibit the CPU from tracing before we disable the TRBE */
-	trfcr = cpu_prohibit_trace();
 	/*
 	 * Ensure the trace is visible to the CPUs and
 	 * any external aborts have been resolved.
 	 */
-	trbe_drain_and_disable_local(cpudata);
+	set_trbe_disabled(cpudata);
 	clr_trbe_irq();
 	isb();
 
@@ -1272,12 +1285,15 @@ static irqreturn_t arm_trbe_irq_handler(int irq, void *dev)
 	 * Otherwise, restore the trace filter controls to
 	 * allow the tracing.
 	 */
-	if (truncated)
+	if (truncated) {
 		irq_work_run();
-	else
-		write_trfcr(trfcr);
+		return IRQ_HANDLED;
+	}
 
-	return IRQ_HANDLED;
+	ret = IRQ_HANDLED;
+out:
+	arm_trbe_allow_trace(trfcr);
+	return ret;
 }
 
 static int arm_trbe_save(struct coresight_device *csdev)

-- 
2.34.1