From b3a81b6c4fc6730ac49e20d789a93c0faabafc98 Mon Sep 17 00:00:00 2001
From: Dmitry Torokhov <dtor@chromium.org>
Date: Wed, 9 May 2018 12:12:15 -0700
Subject: [PATCH] HID: i2c-hid: check if device is there before really probing
Git-commit: b3a81b6c4fc6730ac49e20d789a93c0faabafc98
Patch-mainline: v4.18-rc1
References: bsc#1051510

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@chromium.org>
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 drivers/hid/i2c-hid/i2c-hid.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/hid/i2c-hid/i2c-hid.c b/drivers/hid/i2c-hid/i2c-hid.c
index cf71c33ac2b2..c5ad918e36e3 100644
--- a/drivers/hid/i2c-hid/i2c-hid.c
+++ b/drivers/hid/i2c-hid/i2c-hid.c
@@ -1060,6 +1060,14 @@ static int i2c_hid_probe(struct i2c_client *client,
 	pm_runtime_enable(&client->dev);
 	device_enable_async_suspend(&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;
-- 
2.18.0