[PATCH RFC 6/9] powerpc/pseries: Wakeup hvpipe FD when the payload is pending

[Haren Myneni]

The user space polls on the wait_queue for the payload from the
specific source. The hypervisor interrupts the OS when the pipe
status for the specific source is changed such as payload is
available for the partition or pipe to the source is closed. The
OS retrieves the HVPIPE event message with check-exception RTAS
and event message contains the source ID and the pipe status.
Then wakes up all FDs waiting on the wait_queue so that the user
space can read the payload or close the FD if the pipe to source
in the hypervisor is closed.

The hypervisor assigns one pipe per partition for all sources.
Hence issue  ibm,receive-hvpipe-msg() to read the pending
payload during release() before closing FD so that pipe to the
partition will not be blocked.

Signed-off-by: Haren Myneni <haren at linux.ibm.com>
---
 arch/powerpc/platforms/pseries/papr-hvpipe.c | 28 +++++++++++++++++++-
 1 file changed, 27 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/platforms/pseries/papr-hvpipe.c b/arch/powerpc/platforms/pseries/papr-hvpipe.c
index 21483ea09489..b283837dcefc 100644
--- a/arch/powerpc/platforms/pseries/papr-hvpipe.c
+++ b/arch/powerpc/platforms/pseries/papr-hvpipe.c
@@ -398,6 +398,21 @@ static unsigned int papr_hvpipe_handle_poll(struct file *filp,
 	if (!src_info)
 		return -EIO;
 
+	/*
+	 * If hvpipe already has pending payload, return so that
+	 * the user space can issue read().
+	 */
+	if (src_info->hvpipe_status)
+		return POLLIN | POLLRDNORM;
+
+	/*
+	 * Wait for the message event
+	 * hvpipe_event_interrupt() wakes up this wait_queue
+	 */
+	poll_wait(filp, &src_info->recv_wqh, wait);
+	if (src_info->hvpipe_status)
+		return POLLIN | POLLRDNORM;
+
 	return 0;
 }
 
@@ -415,7 +430,18 @@ static int papr_hvpipe_handle_release(struct inode *inode,
 	src_info = file->private_data;
 	list_del(&src_info->list);
 	file->private_data = NULL;
-	spin_unlock(&hvpipe_src_list_lock);
+	/*
+	 * If the pipe for this specific source has any pending
+	 * payload, issue recv HVPIPE RTAS so that pipe will not
+	 * be blocked.
+	 */
+	if (src_info->hvpipe_status & HVPIPE_MSG_AVAILABLE) {
+		src_info->hvpipe_status = 0;
+		spin_unlock(&hvpipe_src_list_lock);
+		hvpipe_rtas_recv_msg(NULL, 0);
+	} else
+		spin_unlock(&hvpipe_src_list_lock);
+
 	kfree(src_info);
 	return 0;
 }
-- 
2.43.5