On 4/29/19 10:45 AM, Benjamin Tissoires wrote:
>> I would like to ask help from input subsystem experts what kind of SMBus
>> power state dependency Synaptics RMI4 SMBus devices have since it cease
>> to work if SMBus controllers idles between transfers and how this is
>> best to fix?
> 
> Hmm, I am not sure there is such an existing architecture you could
> use in a simple patch.
> 
> rmi-driver.c does indeed create an input device we could use to toggle
> on/off the PM state, but those callbacks are not wired to the
> transport driver (rmi_smbus.c), so it would required a little bit of
> extra work. And then, there are other RMI4 functions (firmware
> upgrade) that would not be happy if PM is in suspend while there is no
> open input node.
> 
I see.

I got another thought about this. I noticed these input drivers need 
SMBus Host Notify, maybe that explain the PM dependency? If that's the 
only dependency then we could prevent the controller suspend if there is 
a client needing host notify mechanism. IMHO that's less hack than the 
patch to rmi_smbus.c.

Keijo: care to test does this idea would fix the issue (without the 
previous patch)? I also attached the diff.

diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c
index 38af18645133..d54eafad7727 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");
+			/* Adapter should not suspend for Host Notify */
+			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;
  }

> So I think this "hack" (with Mika's comments addressed) should go in
> until someone starts propagating the PM states correctly.
> 
I guess you mean the Rafael's pm_runtime_get_sync() comment?

-- 
Jarkko