* Re: AHCI SATA Runtime PM
[not found] <alpine.LNX.2.20.13.2103041814050.15170@monopod.intra.ispras.ru>
@ 2021-03-17 15:02 ` Hans de Goede
0 siblings, 0 replies; only message in thread
From: Hans de Goede @ 2021-03-17 15:02 UTC (permalink / raw)
To: Alexander Monakov, Jens Axboe
Cc: linux-kernel, linux-pm, Zhang Rui, linux-ide
Hi,
On 3/4/21 4:34 PM, Alexander Monakov wrote:
> Hello, Hans, Linux PM folks,
>
> I'm looking for clarification regarding this patch discussion:
>
> https://patchwork.kernel.org/project/linux-pm/patch/20180420101834.15783-2-0v3rdr0n3@gmail.com/
>
> Hans said,
>
>> Ah, so the AHCI code has runtime pm enabled by default (so there
>> is another pm_runtime_allow() somewhere, but then disables it for
>> unused ports to make hotpluging something into those ports work.
>
> I have a laptop where two unused AHCI SATA controllers are present (but
> obviously nothing can be hotplugged into them). Apparently due to the above,
> they do not enter runtime autosuspend.
>
> The problem is, these "ATA port" nodes don't seem to participate in udev
> hierarchy, so it's unclear how I'm supposed to automatically re-enable
> runtime PM for them. For PCI device nodes, I have
>
> ACTION=="add", SUBSYSTEM=="pci", TEST=="power/control", ATTR{power/control}="auto"
>
> but ata1/uevent is empty, so there's no obvious way to write the corresponding
> UDev rule.
You can enable runtime-pm from udev using the following rule:
ACTION=="add", SUBSYSTEM=="ata_port", ATTR{../../power/control}="auto"
> Prior to discovering the above patch discussion, I have filed a bug:
> https://bugzilla.kernel.org/show_bug.cgi?id=211837
>
> Does the above correctly reflect how AHCI PM is supposed to be?
This is a complicated question, I just checked and according to:
https://www.intel.com/content/www/us/en/io/serial-ata/serial-ata-ahci-spec-rev1-3-1.html
AHCI 1.3 compliant controllers should raise a PME signal on hotplug
changes even when in D3. So perhaps the solution is to catch this signal
and then wakeup the controller; and remove the pm_runtime_forbid(dev); call
from ata_tport_add().
I don't have much experience with dealing with the PME stuff, so you will
need to do some research there, or perhaps someone else can help?
This seems to be more of a sata/ahci question then a generic linux-pm question
though, so I have added Jebns and linux-ide to the To / Cc.
> If so, what is
> the proper way to enable runtime PM for unused ATA ports?
Regards,
Hans
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2021-03-17 15:02 ` AHCI SATA Runtime PM Hans de Goede
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