[PATCH v2] i2c: smbus: Send alert notifications to all devices if source not found

[Guenter Roeck <linux@roeck-us.net>]

If a SMBUs alert is received and the originating device is not found,
the reason may be that the address reported on the SMBus alert address
is corrupted, for example because multiple devices asserted alert and
do not correctly implement SMBus arbitration.

If this happens, call alert handlers on all devices connected to the
given I2C bus, in the hope that this cleans up the situation.

This change reliably fixed the problem on a system with multiple devices
on a single bus. Example log where the device on address 0x18 (ADM1021)
and on address 0x4c (ADT7461A) both had the alert line asserted:

smbus_alert 3-000c: SMBALERT# from dev 0x0c, flag 0
smbus_alert 3-000c: no driver alert()!
smbus_alert 3-000c: SMBALERT# from dev 0x0c, flag 0
smbus_alert 3-000c: no driver alert()!
lm90 3-0018: temp1 out of range, please check!
lm90 3-0018: Disabling ALERT#
lm90 3-0029: Everything OK
lm90 3-002a: Everything OK
lm90 3-004c: temp1 out of range, please check!
lm90 3-004c: temp2 out of range, please check!
lm90 3-004c: Disabling ALERT#

Fixes: b5527a7766f0 ("i2c: Add SMBus alert support")
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
---
v2: Simplified: break loop after calling smbus_do_alert_force(),
    and dropped retry variable.
    Rebased on top of target branch.

Based on branch i2c/for-current of
git://git.kernel.org/pub/scm/linux/kernel/git/wsa/linux.git.

 drivers/i2c/i2c-smbus.c | 38 +++++++++++++++++++++++++++++++++++---
 1 file changed, 35 insertions(+), 3 deletions(-)

diff --git a/drivers/i2c/i2c-smbus.c b/drivers/i2c/i2c-smbus.c
index 836c247e7684..2b33c71feae1 100644
--- a/drivers/i2c/i2c-smbus.c
+++ b/drivers/i2c/i2c-smbus.c
@@ -65,6 +65,32 @@ static int smbus_do_alert(struct device *dev, void *addrp)
 	return ret;
 }
 
+/* Same as above, but call back all drivers with alert handler */
+
+static int smbus_do_alert_force(struct device *dev, void *addrp)
+{
+	struct i2c_client *client = i2c_verify_client(dev);
+	struct alert_data *data = addrp;
+	struct i2c_driver *driver;
+
+	if (!client || (client->flags & I2C_CLIENT_TEN))
+		return 0;
+
+	/*
+	 * Drivers should either disable alerts, or provide at least
+	 * a minimal handler. Lock so the driver won't change.
+	 */
+	device_lock(dev);
+	if (client->dev.driver) {
+		driver = to_i2c_driver(client->dev.driver);
+		if (driver->alert)
+			driver->alert(client, data->type, data->data);
+	}
+	device_unlock(dev);
+
+	return 0;
+}
+
 /*
  * The alert IRQ handler needs to hand work off to a task which can issue
  * SMBus calls, because those sleeping calls can't be made in IRQ context.
@@ -106,13 +132,19 @@ static irqreturn_t smbus_alert(int irq, void *d)
 		/*
 		 * If we read the same address more than once, and the alert
 		 * was not handled by a driver, it won't do any good to repeat
-		 * the loop because it will never terminate.
-		 * Bail out in this case.
+		 * the loop because it will never terminate. Try again, this
+		 * time calling the alert handlers of all devices connected to
+		 * the bus, and abort the loop afterwards. If this helps, we
+		 * are all set. If it doesn't, there is nothing else we can do,
+		 * so we might as well abort the loop.
 		 * Note: This assumes that a driver with alert handler handles
 		 * the alert properly and clears it if necessary.
 		 */
-		if (data.addr == prev_addr && status != -EBUSY)
+		if (data.addr == prev_addr && status != -EBUSY) {
+			device_for_each_child(&ara->adapter->dev, &data,
+					      smbus_do_alert_force);
 			break;
+		}
 		prev_addr = data.addr;
 	}
 
-- 
2.39.2