linux-kernel - [PATCH 5.4 19/78] HID: hidraw: Fix returning EPOLLOUT from hidraw

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Date:   Tue, 14 Jan 2020 11:00:53 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Marcel Holtmann <marcel@...tmann.org>,
        Jiri Kosina <jkosina@...e.cz>
Subject: [PATCH 5.4 19/78] HID: hidraw: Fix returning EPOLLOUT from hidraw_poll

From: Marcel Holtmann <marcel@...tmann.org>

commit 9f3b61dc1dd7b81e99e7ed23776bb64a35f39e1a upstream.

When polling a connected /dev/hidrawX device, it is useful to get the
EPOLLOUT when writing is possible. Since writing is possible as soon as
the device is connected, always return it.

Right now EPOLLOUT is only returned when there are also input reports
are available. This works if devices start sending reports when
connected, but some HID devices might need an output report first before
sending any input reports. This change will allow using EPOLLOUT here as
well.

Fixes: 378b80370aa1 ("hidraw: Return EPOLLOUT from hidraw_poll")
Signed-off-by: Marcel Holtmann <marcel@...tmann.org>
Cc: stable@...r.kernel.org
Signed-off-by: Jiri Kosina <jkosina@...e.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/hid/hidraw.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/hid/hidraw.c
+++ b/drivers/hid/hidraw.c
@@ -252,10 +252,10 @@ static __poll_t hidraw_poll(struct file
 
 	poll_wait(file, &list->hidraw->wait, wait);
 	if (list->head != list->tail)
-		return EPOLLIN | EPOLLRDNORM | EPOLLOUT;
+		return EPOLLIN | EPOLLRDNORM;
 	if (!list->hidraw->exist)
 		return EPOLLERR | EPOLLHUP;
-	return 0;
+	return EPOLLOUT | EPOLLWRNORM;
 }
 
 static int hidraw_open(struct inode *inode, struct file *file)