linux-kernel - [PATCH 2/2] i2c: busses with dynamic ids should start after fixed ids for DT

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Date:	Thu, 12 Mar 2015 17:17:59 +0100
From:	Wolfram Sang <wsa@...-dreams.de>
To:	linux-i2c@...r.kernel.org
Cc:	Wolfram Sang <wsa@...-dreams.de>, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	Bob Feretich <bob.feretich@...research.com>,
	Jean Delvare <jdelvare@...e.de>, devicetree@...r.kernel.org
Subject: [PATCH 2/2] i2c: busses with dynamic ids should start after fixed ids for DT

Make sure dynamic ids do not interfere with fixed ones and let them
start after the highest fixed id. This patch might cause different
bus-numbers for dynamic ids, however it fixes a bug. Assume:

- fixed id0 defers probe
- fixed id1 succeeds and registers a muxed bus with dynamic id
- muxed bus gets id0
- fixed id0 wants to probe again, but its fixed id is gone now
- fixed id0 probe fails

With this patch, the fixed ids are always reserved in the DT case.
For legacy board init, we already have a mechanism like this in
i2c_register_board_info().

Reported-by: Bob Feretich <bob.feretich@...research.com>
Signed-off-by: Wolfram Sang <wsa@...-dreams.de>
---
 drivers/i2c/i2c-core.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
index 210cf4874cb7ea..4dda9a529f4464 100644
--- a/drivers/i2c/i2c-core.c
+++ b/drivers/i2c/i2c-core.c
@@ -1878,6 +1878,14 @@ static int __init i2c_init(void)
 {
 	int retval;
 
+	retval = of_alias_get_highest_id("i2c");
+
+	down_write(&__i2c_board_lock);
+	if (retval >= __i2c_first_dynamic_bus_num) {
+		__i2c_first_dynamic_bus_num = retval + 1;
+	}
+	up_write(&__i2c_board_lock);
+
 	retval = bus_register(&i2c_bus_type);
 	if (retval)
 		return retval;
-- 
2.1.4

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