i2c: Prevent runtime suspend of adapter when Host Notify is required [Linux 5.1]

i2c: Prevent runtime suspend of adapter when Host Notify is required [Linux 5.1]

This Linux kernel change "i2c: Prevent runtime suspend of adapter when Host Notify is required" is included in the Linux 5.1 release. This change is authored by Jarkko Nikula <jarkko.nikula [at] linux.intel.com> on Tue Apr 30 17:23:22 2019 +0300. The commit for this change in Linux stable tree is 72bfcee (patch).

i2c: Prevent runtime suspend of adapter when Host Notify is required

Multiple users have reported their Synaptics touchpad has stopped
working between v4.20.1 and v4.20.2 when using SMBus interface.

The culprit for this appeared to be commit c5eb1190074c ("PCI / PM: Allow
runtime PM without callback functions") that fixed the runtime PM for
i2c-i801 SMBus adapter. Those Synaptics touchpad are using i2c-i801
for SMBus communication and testing showed they are able to get back
working by preventing the runtime suspend of adapter.

Normally when i2c-i801 SMBus adapter transmits with the client it resumes
before operation and autosuspends after.

However, if client requires SMBus Host Notify protocol, what those
Synaptics touchpads do, then the host adapter must not go to runtime
suspend since then it cannot process incoming SMBus Host Notify commands
the client may send.

Fix this by keeping I2C/SMBus adapter active in case client requires
Host Notify.

Reported-by: Keijo Vaara <ferdasyn@rocketmail.com>
Link: https://bugzilla.kernel.org/show_bug.cgi?id=203297
Fixes: c5eb1190074c ("PCI / PM: Allow runtime PM without callback functions")
Cc: stable@vger.kernel.org # v4.20+
Signed-off-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Tested-by: Keijo Vaara <ferdasyn@rocketmail.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

There are 4 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 drivers/i2c/i2c-core-base.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c
index 38af186..8149c9e 100644
--- a/drivers/i2c/i2c-core-base.c
+++ b/drivers/i2c/i2c-core-base.c
@@ -327,6 +327,8 @@ static int i2c_device_probe(struct device *dev)

        if (client->flags & I2C_CLIENT_HOST_NOTIFY) {
            dev_dbg(dev, "Using Host Notify IRQ\n");
+           /* Keep adapter active when Host Notify is required */
+           pm_runtime_get_sync(&client->adapter->dev);
            irq = i2c_smbus_host_notify_to_irq(client);
        } else if (dev->of_node) {
            irq = of_irq_get_byname(dev->of_node, "irq");
@@ -431,6 +433,8 @@ static int i2c_device_remove(struct device *dev)
    device_init_wakeup(&client->dev, false);

    client->irq = client->init_irq;
+   if (client->flags & I2C_CLIENT_HOST_NOTIFY)
+       pm_runtime_put(&client->adapter->dev);

    return status;
 }

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