linux-kernel - [PATCH 3.18 43/85] HID: i2c-hid: check if device is there before really probing

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Date:   Tue,  7 Aug 2018 20:51:45 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Dmitry Torokhov <dtor@...omium.org>,
        Benjamin Tissoires <benjamin.tissoires@...hat.com>,
        Jiri Kosina <jkosina@...e.cz>,
        Sasha Levin <alexander.levin@...rosoft.com>
Subject: [PATCH 3.18 43/85] HID: i2c-hid: check if device is there before really probing

3.18-stable review patch.  If anyone has any objections, please let me know.

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

From: Dmitry Torokhov <dtor@...omium.org>

[ Upstream commit b3a81b6c4fc6730ac49e20d789a93c0faabafc98 ]

On many Chromebooks touch devices are multi-sourced; the components are
electrically compatible and one can be freely swapped for another without
changing the OS image or firmware.

To avoid bunch of scary messages when device is not actually present in the
system let's try testing basic communication with it and if there is no
response terminate probe early with -ENXIO.

Signed-off-by: Dmitry Torokhov <dtor@...omium.org>
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@...hat.com>
Signed-off-by: Jiri Kosina <jkosina@...e.cz>
Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/hid/i2c-hid/i2c-hid.c |    8 ++++++++
 1 file changed, 8 insertions(+)

--- a/drivers/hid/i2c-hid/i2c-hid.c
+++ b/drivers/hid/i2c-hid/i2c-hid.c
@@ -981,6 +981,14 @@ static int i2c_hid_probe(struct i2c_clie
 	pm_runtime_set_active(&client->dev);
 	pm_runtime_enable(&client->dev);
 
+	/* Make sure there is something at this address */
+	ret = i2c_smbus_read_byte(client);
+	if (ret < 0) {
+		dev_dbg(&client->dev, "nothing at this address: %d\n", ret);
+		ret = -ENXIO;
+		goto err_pm;
+	}
+
 	ret = i2c_hid_fetch_hid_descriptor(ihid);
 	if (ret < 0)
 		goto err_pm;