[PATCH 3/3] scsi: sync cache on write

[Caleb Connolly]

We don't have a mechanism to safely shutdown block devices prior to a
baord reset or driver removal. Prevent data loss by synchronizing the
SCSI cache after every write.

In particular this solves the issue of capsule updates looping on some
devices because the board resets immediately after deleting the capsule
file and this write wouldn't be flushed in time.

This may impact NAND wear, but should be negligible given the usecases
for disk write in U-Boot.

Signed-off-by: Caleb Connolly <caleb.connolly at linaro.org>
---
 drivers/scsi/scsi.c | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c
index 1aa7fbdbb5278e387de72a3c3e73d19ea0342fff..1b71e580b89b100395ea132a4976366a713cba8a 100644
--- a/drivers/scsi/scsi.c
+++ b/drivers/scsi/scsi.c
@@ -77,8 +77,25 @@ static void scsi_setup_inquiry(struct scsi_cmd *pccb)
 	pccb->cmdlen = 6;
 	pccb->msgout[0] = SCSI_IDENTIFY; /* NOT USED */
 }
 
+static void scsi_setup_sync_cache(struct scsi_cmd *pccb, lbaint_t start,
+				  unsigned short blocks)
+{
+	pccb->cmd[0] = SCSI_SYNC_CACHE;
+	pccb->cmd[1] = 0;
+	pccb->cmd[2] = (unsigned char)(start >> 24) & 0xff;
+	pccb->cmd[3] = (unsigned char)(start >> 16) & 0xff;
+	pccb->cmd[4] = (unsigned char)(start >> 8) & 0xff;
+	pccb->cmd[5] = (unsigned char)start & 0xff;
+	pccb->cmd[6] = 0;
+	pccb->cmd[7] = (unsigned char)(blocks >> 8) & 0xff;
+	pccb->cmd[8] = (unsigned char)blocks & 0xff;
+	pccb->cmd[9] = 0;
+	pccb->cmdlen = 10;
+	pccb->msgout[0] = SCSI_IDENTIFY; /* NOT USED */
+}
+
 static void scsi_setup_read_ext(struct scsi_cmd *pccb, lbaint_t start,
 				unsigned short blocks)
 {
 	pccb->cmd[0] = SCSI_READ10;
@@ -235,8 +252,19 @@ static ulong scsi_write(struct udevice *dev, lbaint_t blknr, lbaint_t blkcnt,
 			blkcnt -= blks;
 			break;
 		}
 
+		/*
+		 * Ensure the writes are flushed to disk so we don't lose data
+		 * on board reset.
+		 * FIXME: this ought to be in a SCSI shutdown path instead
+		 */
+		scsi_setup_sync_cache(pccb, start, smallblks);
+		if (scsi_exec(bdev, pccb)) {
+			scsi_print_error(pccb);
+			break;
+		}
+
 		if (blks > max_blks) {
 			start += max_blks;
 			blks -= max_blks;
 		} else {

-- 
2.49.0