From: Vaibhav Gupta <vaibhavgupta40@gmail.com>
To: Bjorn Helgaas <helgaas@kernel.org>
Cc: Jean Delvare <jdelvare@suse.de>,
Jarkko Nikula <jarkko.nikula@linux.intel.com>,
linux-i2c@vger.kernel.org, Wolfram Sang <wsa@the-dreams.de>,
Mika Westerberg <mika.westerberg@linux.intel.com>,
stable@vger.kernel.org, Bjorn Helgaas <bhelgaas@google.com>,
linux-pci@vger.kernel.org,
"Rafael J. Wysocki" <rjw@rjwysocki.net>,
linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] i2c: i801: Fix runtime PM
Date: Mon, 31 Aug 2020 20:45:30 +0530 [thread overview]
Message-ID: <20200831151159.GA11707@gmail.com> (raw)
In-Reply-To: <20200828162640.GA2160001@bjorn-Precision-5520>
On Fri, Aug 28, 2020 at 11:26:40AM -0500, Bjorn Helgaas wrote:
> [+cc Vaibhav]
>
> On Wed, Jun 27, 2018 at 04:23:40PM -0500, Bjorn Helgaas wrote:
> > [+cc Rafael, linux-pm, linux-kernel]
> >
> > On Wed, Jun 27, 2018 at 10:15:50PM +0200, Jean Delvare wrote:
> > > Hi Jarkko,
> > >
> > > On Tue, 26 Jun 2018 17:39:12 +0300, Jarkko Nikula wrote:
> > > > Commit 9c8088c7988 ("i2c: i801: Don't restore config registers on
> > > > runtime PM") nullified the runtime PM suspend/resume callback pointers
> > > > while keeping the runtime PM enabled. This causes that device stays in
> > > > D0 power state and sysfs /sys/bus/pci/devices/.../power/runtime_status
> > > > shows "error" when runtime PM framework attempts to autosuspend the
> > > > device.
> > > >
> > > > This is due PCI bus runtime PM which checks for driver runtime PM
> > > > callbacks and returns with -ENOSYS if they are not set. Fix this by
> > > > having a shared dummy runtime PM callback that returns with success.
> > > >
> > > > Fixes: a9c8088c7988 ("i2c: i801: Don't restore config registers on runtime PM")
> > >
> > > I don't want to sound like I'm trying to decline all responsibility for
> > > a regression I caused, but frankly, if just using SIMPLE_DEV_PM_OPS()
> > > breaks runtime PM, then it's the PM model which is broken, not the
> > > i2c-i801 driver.
> > >
> > > I will boldly claim that the PCI bus runtime code is simply wrong in
> > > returning -ENOSYS in the absence of runtime PM callbacks, and it should
> > > be changed to return 0 instead. Or whoever receives that -ENOSYS should
> > > not treat it as an error - whatever makes more sense.
> > >
> > > Having to add dummy functions in every PCI driver that doesn't need to
> > > do anything special for runtime PM sounds plain stupid. It should be
> > > pretty obvious that a whole lot of drivers are going to use
> > > SIMPLE_DEV_PM_OPS() because it exists and seems to do what they want,
> > > and all of them will be bugged because the PCI core is doing something
> > > silly and unexpected.
> > >
> > > So please let's fix it at the PCI subsystem core level. Adding Bjorn
> > > and the linux-pci list to Cc.
> >
> > Thanks Jean. What you describe does sound broken. I think the PM
> > guys (cc'd) will have a better idea of how to deal with this.
>
> Did we ever get anywhere with this? It seems like the thread petered
> out.
This does seems worrying. I remember, few days earlier you pointed out a driver
i2c-nvidia-gpuc.c. In the code, gpu_i2c_suspend() is an empty-body function. And
comment mentioned that empty stub is necessary for runtime_pm to work.
And this driver also uses UNIVERSAL_DEV_PM_OPS.
next prev parent reply other threads:[~2020-08-31 15:18 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20180626143913.7361-1-jarkko.nikula@linux.intel.com>
2018-06-27 20:15 ` [PATCH 1/2] i2c: i801: Fix runtime PM Jean Delvare
2018-06-27 21:23 ` Bjorn Helgaas
2020-08-28 16:26 ` Bjorn Helgaas
2020-08-31 15:15 ` Vaibhav Gupta [this message]
2020-09-01 8:19 ` Jarkko Nikula
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200831151159.GA11707@gmail.com \
--to=vaibhavgupta40@gmail.com \
--cc=bhelgaas@google.com \
--cc=helgaas@kernel.org \
--cc=jarkko.nikula@linux.intel.com \
--cc=jdelvare@suse.de \
--cc=linux-i2c@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-pci@vger.kernel.org \
--cc=linux-pm@vger.kernel.org \
--cc=mika.westerberg@linux.intel.com \
--cc=rjw@rjwysocki.net \
--cc=stable@vger.kernel.org \
--cc=wsa@the-dreams.de \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).