linux-kernel - [PATCH 3.16 170/245] HID: hidraw: Fix returning EPOLLOUT from hidraw

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Message-ID: <lsq.1587683028.312246222@decadent.org.uk>
Date:   Fri, 24 Apr 2020 00:06:37 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Marcel Holtmann" <marcel@...tmann.org>,
        "Jiri Kosina" <jkosina@...e.cz>
Subject: [PATCH 3.16 170/245] HID: hidraw: Fix returning EPOLLOUT from
 hidraw_poll

3.16.83-rc1 review patch.  If anyone has any objections, please let me know.

------------------

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>
Signed-off-by: Jiri Kosina <jkosina@...e.cz>
[bwh: Backported to 3.16: s/EPOLL/POLL/g]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/hid/hidraw.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/hid/hidraw.c
+++ b/drivers/hid/hidraw.c
@@ -265,10 +265,10 @@ static unsigned int hidraw_poll(struct f
 
 	poll_wait(file, &list->hidraw->wait, wait);
 	if (list->head != list->tail)
-		return POLLIN | POLLRDNORM | POLLOUT;
+		return POLLIN | POLLRDNORM;
 	if (!list->hidraw->exist)
 		return POLLERR | POLLHUP;
-	return 0;
+	return POLLOUT | POLLWRNORM;
 }
 
 static int hidraw_open(struct inode *inode, struct file *file)