From 88aca1377f55f0cf1eab46731a77a459724a920d Mon Sep 17 00:00:00 2001
From: Ezequiel Garcia <ezequiel@collabora.com>
Date: Sun, 21 Mar 2021 16:38:54 -0300
Subject: [PATCH] RFC: media: Add media_request_{pin,unpin} API

This is probably not the API we will want to add, but it
should show what semantics are needed by drivers.

The goal is to allow the OUTPUT (aka source) buffer and the
controls associated to a request to be released from the request,
and in particular return the OUTPUT buffer back to userspace,
without signalling the media request fd.

This is useful for devices that are able to pre-process
the OUTPUT buffer, therefore able to release it before
the decoding is finished. These drivers should signal
the media request fd only after the CAPTURE buffer is done.

Tested-by: John Cox <jc@kynesim.co.uk>
Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
---
 drivers/media/mc/mc-request.c | 35 +++++++++++++++++++++++++++++++++++
 include/media/media-request.h | 12 ++++++++++++
 2 files changed, 47 insertions(+)

--- a/drivers/media/mc/mc-request.c
+++ b/drivers/media/mc/mc-request.c
@@ -505,3 +505,38 @@ unlock:
 		media_request_put(req);
 }
 EXPORT_SYMBOL_GPL(media_request_object_complete);
+
+void media_request_pin(struct media_request *req)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&req->lock, flags);
+	if (WARN_ON(req->state != MEDIA_REQUEST_STATE_QUEUED))
+		goto unlock;
+	req->num_incomplete_objects++;
+unlock:
+	spin_unlock_irqrestore(&req->lock, flags);
+}
+EXPORT_SYMBOL_GPL(media_request_pin);
+
+void media_request_unpin(struct media_request *req)
+{
+	unsigned long flags;
+	bool completed = false;
+
+	spin_lock_irqsave(&req->lock, flags);
+	if (WARN_ON(!req->num_incomplete_objects) ||
+	    WARN_ON(req->state != MEDIA_REQUEST_STATE_QUEUED))
+		goto unlock;
+
+	if (!--req->num_incomplete_objects) {
+		req->state = MEDIA_REQUEST_STATE_COMPLETE;
+		wake_up_interruptible_all(&req->poll_wait);
+		completed = true;
+	}
+unlock:
+	spin_unlock_irqrestore(&req->lock, flags);
+	if (completed)
+		media_request_put(req);
+}
+EXPORT_SYMBOL_GPL(media_request_unpin);
--- a/include/media/media-request.h
+++ b/include/media/media-request.h
@@ -189,6 +189,10 @@ static inline void media_request_get(str
  */
 void media_request_put(struct media_request *req);
 
+void media_request_pin(struct media_request *req);
+
+void media_request_unpin(struct media_request *req);
+
 /**
  * media_request_get_by_fd - Get a media request by fd
  *
@@ -228,6 +232,14 @@ static inline void media_request_put(str
 {
 }
 
+static inline void media_request_pin(struct media_request *req)
+{
+}
+
+static inline void media_request_unpin(struct media_request *req)
+{
+}
+
 static inline struct media_request *
 media_request_get_by_fd(struct media_device *mdev, int request_fd)
 {
