[PATCH 5/5] cxl/mbox: Retry sending mbox command upon RETRY return_code

[Davidlohr Bueso <dave@stgolabs.net>]

As mentioned in CXL 2.0 specs: the hardware can set a Retry
Required if the the command was not completed due to a
temporary error. An optional single retry may resolve the
issue. This is the only retry case as in general they are
not recommended for commands that return an error.

Signed-off-by: Davidlohr Bueso <dave@stgolabs.net>
---
 drivers/cxl/core/mbox.c | 23 ++++++++++++++---------
 1 file changed, 14 insertions(+), 9 deletions(-)

diff --git a/drivers/cxl/core/mbox.c b/drivers/cxl/core/mbox.c
index fa9e7043f158..567987052b68 100644
--- a/drivers/cxl/core/mbox.c
+++ b/drivers/cxl/core/mbox.c
@@ -160,20 +160,25 @@ int cxl_mbox_send_cmd(struct cxl_dev_state *cxlds, u16 opcode, void *in,
 		.size_out = out_size,
 		.payload_out = out,
 	};
-	int rc;
+	int rc, retry = 1;
 
 	if (out_size > cxlds->payload_size)
 		return -E2BIG;
 
-	/* acquire and releases the mbox_mutex */
-	rc = cxlds->mbox_send(cxlds, &mbox_cmd);
-	if (rc)
-		return rc;
+	do {
+		/* acquire and releases the mbox_mutex */
+		rc = cxlds->mbox_send(cxlds, &mbox_cmd);
+		if (rc)
+			return rc;
 
-	if (mbox_cmd.return_code != CXL_MBOX_CMD_RC_SUCCESS) {
-		int err = cxl_mbox_cmd_rc2errno(&mbox_cmd);
-		return -err;
-	}
+		if (mbox_cmd.return_code == CXL_MBOX_CMD_RC_SUCCESS)
+			break;
+
+		if (mbox_cmd.return_code != CXL_MBOX_CMD_RC_RETRY || !retry) {
+			int err = cxl_mbox_cmd_rc2errno(&mbox_cmd);
+			return -err;
+		}
+	} while (retry--);
 
 	/*
 	 * Variable sized commands can't be validated and so it's up to the
-- 
2.26.2