linux-kernel - Re: [PATCH v3 1/5] PM: sleep: Resume children after resuming the parent

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Message-ID: <b17469ee-0d8c-49ff-8fc8-a3c3cc9964dd@nvidia.com>
Date: Wed, 7 May 2025 16:39:50 +0100
From: Jon Hunter <jonathanh@...dia.com>
To: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>,
 Linux PM <linux-pm@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
 Alan Stern <stern@...land.harvard.edu>, Ulf Hansson
 <ulf.hansson@...aro.org>, Johan Hovold <johan@...nel.org>,
 Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
 Saravana Kannan <saravanak@...gle.com>,
 "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH v3 1/5] PM: sleep: Resume children after resuming the
 parent

On 07/05/2025 15:56, Rafael J. Wysocki wrote:

...

> So apparently one of the children has not been suspended yet when this
> happens.  That's fine because it should be suspended at one point and
> the parent suspend should be unblocked, so it looks like the child
> suspend doesn't complete for some reason.
> 
>> I will enable the PM_ADVANCED_DEBUG and confirm that making the I2C
>> itself non-async works.
> 
> What probably happens is that after the "PM: sleep: Suspend async
> parents after suspending children" , the i2c clients are suspended
> upfront (because they have no children) and when one of them has
> suspended, it triggers a parent suspend.  The parent suspend then
> waits for the other client to complete suspending, but that cannot
> make progress for some reason.
> 
> Before that patch, the i2c clients would have suspended only after all
> of the "sync" devices following them in dpm_list had been suspended
> (the list is processed in the reverse order during suspend), so it
> looks like there is a hidden dependency between one of the i2c clients
> and a "sync" device.
> 
> If the above supposition is right, flagging the i2c client as "sync"
> will make the problem go away.

So all the I2C controllers are 'sync' devices ...

$ cat /sys/class/i2c-dev/i2c-*/power/async
disabled
disabled
disabled
disabled
disabled
disabled
disabled

The I2C clients on the problematic I2C controller are all 'async' 
devices ...

$ cat /sys/class/i2c-dev/i2c-2/device/2-*/power/async
enabled
enabled
enabled

Setting all these to 'disabled' fixes the problem. However, also just 
setting the 'cypd4226' device to 'sync' fixes the problem (the ina3221 
devices seem to be fine being async). The 'cypd4226' device is 
interesting, because this one is a USB Type-C controller and there is a 
circular dependency between the Type-C and USB PHY (see 
arch/arm64/boot/dts/nvidia/tegra194-p2972-0000.dts).

If I make the following change then this does fix it ...

diff --git a/drivers/usb/typec/ucsi/ucsi_ccg.c 
b/drivers/usb/typec/ucsi/ucsi_ccg.c
index f01e4ef6619d..e9a9df1431af 100644
--- a/drivers/usb/typec/ucsi/ucsi_ccg.c
+++ b/drivers/usb/typec/ucsi/ucsi_ccg.c
@@ -1483,6 +1483,8 @@ static int ucsi_ccg_probe(struct i2c_client *client)

         i2c_set_clientdata(client, uc);

+       device_disable_async_suspend(uc->dev);
+
         pm_runtime_set_active(uc->dev);
         pm_runtime_enable(uc->dev);
         pm_runtime_use_autosuspend(uc->dev);

Is this the right fix for this?

Jon

-- 
nvpublic