coresight: trbe: Fix handling of spurious interrupts

On a spurious IRQ, right now we disable the TRBE and then re-enable
it back, resetting the "buffer" pointers(i.e BASE, LIMIT and more
importantly WRITE) to the original pointers from the AUX handle.
This implies that we overwrite any trace that was written so far,
(by overwriting TRBPTR) while we should have ignored the IRQ.

On detecting a spurious IRQ after examining the TRBSR we simply
re-enable the TRBE without touching the other parameters.

Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Cc: Mike Leach <mike.leach@linaro.org>
Cc: Leo Yan <leo.yan@linaro.org>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20210923143919.2944311-3-suzuki.poulose@arm.comSigned-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>

drivers/hwtracing/coresight/coresight-trbe.c

@@ -684,20 +684,16 @@ static int arm_trbe_disable(struct coresight_device *csdev)
 
 static void trbe_handle_spurious(struct perf_output_handle *handle)
 {
-	struct trbe_buf *buf = etm_perf_sink_config(handle);
+	u64 limitr = read_sysreg_s(SYS_TRBLIMITR_EL1);
 
-	buf->trbe_limit = compute_trbe_buffer_limit(handle);
-	buf->trbe_write = buf->trbe_base + PERF_IDX2OFF(handle->head, buf);
-	if (buf->trbe_limit == buf->trbe_base) {
-		trbe_drain_and_disable_local();
 	/*
-		 * Just communicate trace truncation event to the user space by
-		 * marking it with PERF_AUX_FLAG_TRUNCATED.
+	 * If the IRQ was spurious, simply re-enable the TRBE
+	 * back without modifying the buffer parameters to
+	 * retain the trace collected so far.
 	 */
-		perf_aux_output_flag(handle, PERF_AUX_FLAG_TRUNCATED);
-		return;
-	}
-	trbe_enable_hw(buf);
+	limitr |= TRBLIMITR_ENABLE;
+	write_sysreg_s(limitr, SYS_TRBLIMITR_EL1);
+	isb();
 }
 
 static void trbe_handle_overflow(struct perf_output_handle *handle)