[PATCH] lib: sbi: Prevent redundant sbi_ipi_process

[Xiang W]

sbi_ipi_process reads ipi_type through xchg. This may occur between
set ipi_type and send_ipi, which will result in redundant interrupt
processing.

The specific case is as follows:

                hart A             hart B
send ipi--------->|                  |
                  | clear ipi        |
                  |                  | set ipi_type
                  |                  |
                  | xchg ipi_type    |
                  |                  |
                  |<-----------------| send ipi
                  |                  |
                  |                  |

This patch fixes this issue.

Signed-off-by: Xiang W <wxjstz at 126.com>
---
 lib/sbi/sbi_ipi.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/lib/sbi/sbi_ipi.c b/lib/sbi/sbi_ipi.c
index 0bf446a..6f25a7e 100644
--- a/lib/sbi/sbi_ipi.c
+++ b/lib/sbi/sbi_ipi.c
@@ -39,7 +39,7 @@ static const struct sbi_ipi_event_ops *ipi_ops_array[SBI_IPI_EVENT_MAX];
 static int sbi_ipi_send(struct sbi_scratch *scratch, u32 remote_hartindex,
 			u32 event, void *data)
 {
-	int ret;
+	int ret = 0;
 	struct sbi_scratch *remote_scratch = NULL;
 	struct sbi_ipi_data *ipi_data;
 	const struct sbi_ipi_event_ops *ipi_ops;
@@ -66,9 +66,8 @@ static int sbi_ipi_send(struct sbi_scratch *scratch, u32 remote_hartindex,
 	 * Set IPI type on remote hart's scratch area and
 	 * trigger the interrupt
 	 */
-	atomic_raw_set_bit(event, &ipi_data->ipi_type);
-
-	ret = sbi_ipi_raw_send(remote_hartindex);
+	if (__atomic_fetch_or(&ipi_data->ipi_type, BIT(event), __ATOMIC_ACQ_REL) == 0)
+		ret = sbi_ipi_raw_send(remote_hartindex);
 
 	sbi_pmu_ctr_incr_fw(SBI_PMU_FW_IPI_SENT);
 
-- 
2.42.0