platform/surface: aggregator: Add error injection capabilities

This commit adds error injection hooks to the Surface Serial Hub
communication protocol implementation, to:

 - simulate simple serial transmission errors,

 - drop packets, requests, and responses, simulating communication
   failures and potentially trigger retransmission timeouts, as well as

 - inject invalid data into submitted and received packets.

Together with the trace points introduced in the previous commit, these
facilities are intended to aid in testing, validation, and debugging of
the Surface Aggregator communication layer.

Signed-off-by: Maximilian Luz <[email protected]>
Reviewed-by: Hans de Goede <[email protected]>
Acked-by: Steven Rostedt (VMware) <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Hans de Goede <[email protected]>

1 files changed, 35 insertions, 0 deletions

diff --git a/drivers/platform/surface/aggregator/ssh_request_layer.c b/drivers/platform/surface/aggregator/ssh_request_layer.c
index b649d71840fd..bb1c862411a2 100644
--- a/drivers/platform/surface/aggregator/ssh_request_layer.c
+++ b/drivers/platform/surface/aggregator/ssh_request_layer.c
@@ -8,6 +8,7 @@
 #include <asm/unaligned.h>
 #include <linux/atomic.h>
 #include <linux/completion.h>
+#include <linux/error-injection.h>
 #include <linux/ktime.h>
 #include <linux/limits.h>
 #include <linux/list.h>
@@ -58,6 +59,30 @@
  */
 #define SSH_RTL_TX_BATCH		10
 
+#ifdef CONFIG_SURFACE_AGGREGATOR_ERROR_INJECTION
+
+/**
+ * ssh_rtl_should_drop_response() - Error injection hook to drop request
+ * responses.
+ *
+ * Useful to cause request transmission timeouts in the driver by dropping the
+ * response to a request.
+ */
+static noinline bool ssh_rtl_should_drop_response(void)
+{
+	return false;
+}
+ALLOW_ERROR_INJECTION(ssh_rtl_should_drop_response, TRUE);
+
+#else
+
+static inline bool ssh_rtl_should_drop_response(void)
+{
+	return false;
+}
+
+#endif
+
 static u16 ssh_request_get_rqid(struct ssh_request *rqst)
 {
 	return get_unaligned_le16(rqst->packet.data.ptr
@@ -459,6 +484,16 @@ static void ssh_rtl_complete(struct ssh_rtl *rtl,
 		if (unlikely(ssh_request_get_rqid(p) != rqid))
 			continue;
 
+		/* Simulate response timeout. */
+		if (ssh_rtl_should_drop_response()) {
+			spin_unlock(&rtl->pending.lock);
+
+			trace_ssam_ei_rx_drop_response(p);
+			rtl_info(rtl, "request error injection: dropping response for request %p\n",
+				 &p->packet);
+			return;
+		}
+
 		/*
 		 * Mark as "response received" and "locked" as we're going to
 		 * complete it.