linux-kernel - [PATCH 4.14 02/71] HID: hidraw: Fix returning EPOLLOUT from hidraw

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Date:   Fri, 17 Jan 2020 00:18:00 +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>, Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.14 02/71] HID: hidraw: Fix returning EPOLLOUT from hidraw_poll

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

[ Upstream commit 9f3b61dc1dd7b81e99e7ed23776bb64a35f39e1a ]

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: Sasha Levin <sashal@...nel.org>
---
 drivers/hid/hidraw.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/hid/hidraw.c b/drivers/hid/hidraw.c
index 1ac82e194818..1abf5008def0 100644
--- a/drivers/hid/hidraw.c
+++ b/drivers/hid/hidraw.c
@@ -260,10 +260,10 @@ static unsigned int hidraw_poll(struct file *file, poll_table *wait)
 
 	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)
-- 
2.20.1