Edward O'Callaghan has uploaded this change for review.

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raiden_debug_spi.c: Implement retry mechanism

This overcomes a problem with the ServoMicro where USB packets can be
ack'd by the device without triggering interrupts or loading data into
the USB endpoints. The retry mechanism attempts the USB read 3 times
before reattempting the write call to avoid performing multiple SPI
transfers due to a USB problem. This process repeats 3 times before we
return the last error code. Intermediary problems are reported in the
status code.

Based off the downstream commit:
  https://chromium-review.googlesource.com/c/chromiumos/third_party/flashrom/+/2038271

Change-Id: I76cde68852fa4963582d57c7dcb9f24de32c6da8
Signed-off-by: Edward O'Callaghan <quasisec@google.com>
---
M raiden_debug_spi.c
1 file changed, 42 insertions(+), 8 deletions(-)

git pull ssh://review.coreboot.org:29418/flashrom refs/changes/10/39310/1

diff --git a/raiden_debug_spi.c b/raiden_debug_spi.c
index 08f8928..1f30b6a 100644
--- a/raiden_debug_spi.c
+++ b/raiden_debug_spi.c
@@ -133,6 +133,16 @@
 #define PAYLOAD_SIZE            (MAX_PACKET_SIZE - PACKET_HEADER_SIZE)
 
 /*
+ * Servo Micro has an error where it is capable of acknowledging USB packets
+ * without loading it into the USB endpoint buffers or triggering interrupts.
+ * See crbug.com/952494. Retry mechanisms have been implemented to recover
+ * from these rare failures allowing the process to continue.
+ */
+#define WRITE_RETY_ATTEMPTS     (3)
+#define READ_RETY_ATTEMPTS      (3)
+#define RETY_INTERVAL_US        (100 * 1000)
+
+/*
  * This timeout is so large because the Raiden SPI timeout is 800ms.
  */
 #define TRANSFER_TIMEOUT_MS     (200 + 800)
@@ -245,16 +255,40 @@
 {
 	int status = -1;
 
-	status = write_command(flash, write_count, read_count,
-			write_buffer, read_buffer);
+	for (int write_attempt = 0; write_attempt < WRITE_RETY_ATTEMPTS;
+	         write_attempt++) {
 
-	if (status) {
-		return status;
+		status = write_command(flash, write_count, read_count,
+		                       write_buffer, read_buffer);
+
+		if (status) {
+			/* Write operation failed. */
+			msg_perr("Raiden: Write command failed\n"
+				"Write attempt = %d\n"
+				"status = %d\n",
+				write_attempt + 1, status);
+			programmer_delay(RETY_INTERVAL_US);
+			continue;
+		}
+		for (int read_attempt = 0; read_attempt < READ_RETY_ATTEMPTS; read_attempt++) {
+
+			status = read_response(flash, write_count, read_count,
+					write_buffer, read_buffer);
+
+			if (status != 0) {
+				/* Read operation failed. */
+				msg_perr("Raiden: Read response failed\n"
+					"Write attempt = %d\n"
+					"Read attempt = %d\n"
+					"status = %d\n",
+					write_attempt + 1, read_attempt + 1, status);
+				programmer_delay(RETY_INTERVAL_US);
+			} else {
+				/* We were successful at performing the SPI transfer. */
+				return status;
+			}
+		}
 	}
-
-	status = read_response(flash, write_count, read_count,
-			write_buffer, read_buffer);
-
 	return status;
 }
 

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