linux-kernel - Re: [PATCH v3] PM: add kernel parameter to disable asynchronous suspend/resume

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Message-ID: <47d5f907-f2a9-4a4a-91b3-0cf6ea997678@infradead.org>
Date: Wed, 9 Jul 2025 08:47:48 -0700
From: Randy Dunlap <rdunlap@...radead.org>
To: Tudor Ambarus <tudor.ambarus@...aro.org>, Jonathan Corbet
 <corbet@....net>, "Rafael J. Wysocki" <rafael@...nel.org>,
 Pavel Machek <pavel@...nel.org>, Len Brown <len.brown@...el.com>
Cc: linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-pm@...r.kernel.org, peter.griffin@...aro.org,
 andre.draszik@...aro.org, willmcvicker@...gle.com, kernel-team@...roid.com
Subject: Re: [PATCH v3] PM: add kernel parameter to disable asynchronous
 suspend/resume



On 7/9/25 5:31 AM, Tudor Ambarus wrote:
> On some platforms, device dependencies are not properly represented by
> device links, which can cause issues when asynchronous power management
> is enabled. While it is possible to disable this via sysfs, doing so
> at runtime can race with the first system suspend event.
> 
> This patch introduces a kernel command-line parameter, "pm_async", which
> can be set to "off" to globally disable asynchronous suspend and resume
> operations from early boot. It effectively provides a way to set the
> initial value of the existing pm_async sysfs knob at boot time. This
> offers a robust method to fall back to synchronous (sequential) operation,
> which can stabilize platforms with problematic dependencies and also
> serve as a useful debugging tool.
> 
> The default behavior remains unchanged (asynchronous enabled). To disable
> it, boot the kernel with the "pm_async=off" parameter.
> 
> Signed-off-by: Tudor Ambarus <tudor.ambarus@...aro.org>
> ---
> Dealing with the pixel6 downstream drivers to cope with the changes from
> https://lore.kernel.org/linux-pm/10629535.nUPlyArG6x@rjwysocki.net/.
> 
> Similar to what people already reported it seems pixel6 lacks proper
> device links dependencies downstream causing i2c and spi client drivers
> to fail to suspend. Add kernel param to disable async suspend/resume.
> ---
> Changes in v3:
> - update documentation with "pm_async=" and "Format: off" (Randy)
> - reword documentation to make it clear "on" isn't a selectable option
>   for pm_async because it's the default behavior.
> - Link to v2: https://lore.kernel.org/r/20250708-pm-async-off-v2-1-7fada54f01c0@linaro.org
> 
> Changes in v2:
> - update the documentation and the commit message to describe that the
>   "pm_async" kernel parameter provides a way to change the initial value
>   of the existing /sys/power/pm_async sysfs knob.
> - Link to v1: https://lore.kernel.org/r/20250708-pm-async-off-v1-1-1b200cc03d9c@linaro.org
> ---
>  Documentation/admin-guide/kernel-parameters.txt | 12 ++++++++++++
>  kernel/power/main.c                             |  9 +++++++++
>  2 files changed, 21 insertions(+)
> 

Acked-by: Randy Dunlap <rdunlap@...radead.org>

Thanks.
-- 
~Randy