[PATCH v3 10/10] mtd: powernv_flash: Use opal_async_wait_response_interruptible()

[Cyril Bur <cyrilbur@gmail.com>]

The OPAL calls performed in this driver shouldn't be using
opal_async_wait_response() as this performs a wait_event() which, on
long running OPAL calls could result in hung task warnings. wait_event()
prevents timely signal delivery which is also undesirable.

This patch also attempts to quieten down the use of dev_err() when
errors haven't actually occurred and also to return better information up
the stack rather than always -EIO.

Signed-off-by: Cyril Bur <cyrilbur@gmail.com>
---
 drivers/mtd/devices/powernv_flash.c | 28 +++++++++++++++++++++++-----
 1 file changed, 23 insertions(+), 5 deletions(-)

diff --git a/drivers/mtd/devices/powernv_flash.c b/drivers/mtd/devices/powernv_flash.c
index d7243b72ba6e..cfa274ba7e40 100644
--- a/drivers/mtd/devices/powernv_flash.c
+++ b/drivers/mtd/devices/powernv_flash.c
@@ -90,16 +90,34 @@ static int powernv_flash_async_op(struct mtd_info *mtd, enum flash_op op,
 		goto out_success;
 
 	if (rc != OPAL_ASYNC_COMPLETION) {
-		dev_err(dev, "opal_flash_async_op(op=%d) failed (rc %d)\n",
+		if (rc != OPAL_BUSY)
+			dev_err(dev, "opal_flash_async_op(op=%d) failed (rc %d)\n",
 				op, rc);
-		rc = -EIO;
+		rc = opal_error_code(rc);
 		goto out;
 	}
 
-	rc = opal_async_wait_response(token, &msg);
+	rc = opal_async_wait_response_interruptible(token, &msg);
 	if (rc) {
-		dev_err(dev, "opal async wait failed (rc %d)\n", rc);
-		rc = -EIO;
+		/*
+		 * Awkward, we've been interrupted but we cannot return. If we
+		 * do return the mtd core will free the buffer we've just
+		 * passed to OPAL but OPAL will continue to read or write from
+		 * that memory.
+		 * Future work will introduce a call to tell OPAL to stop
+		 * using the buffer.
+		 * It may be tempting to ultimately return 0 if we're doing a
+		 * read or a write since we are going to end up waiting until
+		 * OPAL is done. However, because the MTD core sends us the
+		 * userspace request in chunks, we must report EINTR so that
+		 * it doesn't just send us the next chunk, thus defeating the
+		 * point of the _interruptible wait.
+		 */
+		rc = -EINTR;
+		if (op == FLASH_OP_READ || op == FLASH_OP_WRITE) {
+			if (opal_async_wait_response(token, &msg))
+				dev_err(dev, "opal async wait failed (rc %d)\n", rc);
+		}
 		goto out;
 	}
 
-- 
2.13.2