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

[Jon Hunter]

Hi Rafael,

On 14/03/2025 12:50, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
>
> According to [1], the handling of device suspend and resume, and
> particularly the latter, involves unnecessary overhead related to
> starting new async work items for devices that cannot make progress
> right away because they have to wait for other devices.
>
> To reduce this problem in the resume path, use the observation that
> starting the async resume of the children of a device after resuming
> the parent is likely to produce less scheduling and memory management
> noise than starting it upfront while at the same time it should not
> increase the resume duration substantially.
>
> Accordingly, modify the code to start the async resume of the device's
> children when the processing of the parent has been completed in each
> stage of device resume and only start async resume upfront for devices
> without parents.
>
> Also make it check if a given device can be resumed asynchronously
> before starting the synchronous resume of it in case it will have to
> wait for another that is already resuming asynchronously.
>
> In addition to making the async resume of devices more friendly to
> systems with relatively less computing resources, this change is also
> preliminary for analogous changes in the suspend path.
>
> On the systems where it has been tested, this change by itself does
> not affect the overall system resume duration in a measurable way.
>
> Link: https://lore.kernel.org/linux-pm/20241114220921.2529905-1-saravanak@xxxxxxxxxx/ [1]
> Suggested-by: Saravana Kannan <saravanak@xxxxxxxxxx>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>


I have noticed a suspend regression with -next on a couple of our Tegra 
boards. Bisect was pointing to the following merge commit ...

# first bad commit: [218a7bbf861f83398ac9767620e91983e36eac05] Merge 
branch 'pm-sleep' into linux-next

On top of next-20250429 I found that by reverting the following changes 
that suspend is working again ...

Revert "PM: sleep: Resume children after resuming the parent"
Revert "PM: sleep: Suspend async parents after suspending children"
Revert "PM: sleep: Make suspend of devices more asynchronous"

I have been looking into this a bit more to see what device is failing 
and by adding a bit of debug I found that entry to suspend was failing 
on the Tegra194 Jetson AGX Xavier (tegra194-p2972-0000.dts) platform 
when one of the I2C controllers (i2c@c240000) was being suspended.

I found that if I disable only this I2C controller in device-tree 
suspend worked again on top of -next. This I2C controller has 3 devices 
on the platform; two ina3221 devices and one Cypress Type-C controller. 
I then found that removing only the two ina3221 devices (in 
tegra194-p2888.dtsi) also allows suspend to work.

At this point, I am still unclear why this is now failing.  If you have 
any thoughts or things I can try please let me know.

Thanks!
Jon

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nvpublic