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From:   Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
To:     Wolfram Sang <wsa@kernel.org>, Jean Delvare <jdelvare@suse.de>
Cc:     Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Mika Westerberg <mika.westerberg@linux.intel.com>,
        linux-i2c@vger.kernel.org, linux-acpi@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Subject: [PATCH] i2c: do not acpi/of match device in i2c_device_probe()
Date:   Wed, 26 Aug 2020 23:49:20 +0900
Message-Id: <20200826144920.110605-1-sergey.senozhatsky@gmail.com>
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Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

i2c, apparently, can match the same device twice - the first
time in ->match bus hook (i2c_device_match()), and the second
one in ->probe (i2c_device_probe()) bus hook.

To make things more complicated, the second matching does not
do exactly same checks as the first one. Namely, i2c_device_match()
calls acpi_driver_match_device() which considers devices that
provide of_match_table and performs of_compatible() matching for
such devices. One important thing to note here is that ACPI
of_compatible() matching (acpi_of_match_device()) is part of ACPI
and does not depend on CONFIG_OF.

i2c_device_probe(), on the other hand, calls acpi_match_device()
which does not perform of_compatible() matching, but instead
i2c_device_probe() relies on CONFIG_OF API to perform of_match_table
matching, IOW ->probe matching, unlike ->match matching, depends on
CONFIG_OF. This can break i2c device probing on !CONFIG_OF systems
if the device does not provide .id_table.

 i2c_device_probe()
 ...
   if (!driver->id_table &&
       !i2c_acpi_match_device(dev->driver->acpi_match_table, client) &&
       !i2c_of_match_device(dev->driver->of_match_table, client)) {
       status = -ENODEV;
       goto put_sync_adapter;
   }

i2c_of_match_device() on !CONFIG_OF systems is always false, so we never
perform of_match_table matching. i2c_acpi_match_device() does ACPI match
only, no of_compatible() matching takes place, even though the device
provides .of_match_table and ACPI is capable of matching such device.

It is not entirely clear why the device is matched again in bus
->probe after successful and proper matching in bus ->match. Let's
remove ->probe matching.

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Suggested-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
---
 drivers/i2c/i2c-core-base.c | 11 -----------
 1 file changed, 11 deletions(-)

diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c
index 5ec082e2039d..77eea5c0bc71 100644
--- a/drivers/i2c/i2c-core-base.c
+++ b/drivers/i2c/i2c-core-base.c
@@ -475,17 +475,6 @@ static int i2c_device_probe(struct device *dev)
 
 	driver = to_i2c_driver(dev->driver);
 
-	/*
-	 * An I2C ID table is not mandatory, if and only if, a suitable OF
-	 * or ACPI ID table is supplied for the probing device.
-	 */
-	if (!driver->id_table &&
-	    !acpi_driver_match_device(dev, dev->driver) &&
-	    !i2c_of_match_device(dev->driver->of_match_table, client)) {
-		status = -ENODEV;
-		goto put_sync_adapter;
-	}
-
 	if (client->flags & I2C_CLIENT_WAKE) {
 		int wakeirq;
 
-- 
2.28.0