linux-kernel - Re: [PATCH v1] PCI / PM: Really allow runtime PM without callback functions

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Date: Wed, 14 Feb 2024 08:58:48 +0200
From: Jarkko Nikula <jarkko.nikula@...ux.intel.com>
To: Bjorn Helgaas <helgaas@...nel.org>, Raag Jadav <raag.jadav@...el.com>
Cc: bhelgaas@...gle.com, mika.westerberg@...ux.intel.com,
 andriy.shevchenko@...ux.intel.com, stanislaw.gruszka@...ux.intel.com,
 lukas@...ner.de, rafael@...nel.org, ilpo.jarvinen@...ux.intel.com,
 linux-pci@...r.kernel.org, linux-pm@...r.kernel.org,
 linux-kernel@...r.kernel.org, gregkh@...uxfoundation.org, sashal@...nel.org
Subject: Re: [PATCH v1] PCI / PM: Really allow runtime PM without callback
 functions

Hi

On 2/13/24 22:06, Bjorn Helgaas wrote:
>> Debugged-by: Mika Westerberg <mika.westerberg@...ux.intel.com>
> 
> Sounds like this resolves a problem report?  Is there a URL we can
> cite?  If not, at least a mention of what the user-visible problem is?
> 
>  From the c5eb1190074c commit log, it sounds like maybe this allows
> devices to be autosuspended when they previously could not be?
> 
> Possibly this should have "Fixes: c5eb1190074c ("PCI / PM: Allow
> runtime PM without callback functions")" since it sounds like it goes
> with it?
> 
I don't think there's known regression but my above commit wasn't 
complete. Autosuspending works without runtime PM callback as long as 
the driver has the PM callbacks structure set.

For example the drivers/i2c/busses/i2c-i801.c has system suspend/resume 
callbacks. I tested this patch by hack-removing them and yes, 
autosuspend doesn't work without this patch.

Raag and Mika noticed the issue when cleaning up empty runtime PM 
callbacks from an another driver which doesn't have any other PM callbacks.