netdev - Re: [PATCH] PCI / tg3: Give up chip reset and carrier loss handling if PCI device is not present

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Date:	Mon, 02 Dec 2013 02:18:50 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Michael Chan <mchan@...adcom.com>
Cc:	netdev@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	Linux PM list <linux-pm@...r.kernel.org>,
	Linux PCI <linux-pci@...r.kernel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Nithin Nayak Sujir <nsujir@...adcom.com>,
	David Miller <davem@...emloft.net>
Subject: Re: [PATCH] PCI / tg3: Give up chip reset and carrier loss handling if PCI device is not present

On Sunday, December 01, 2013 12:39:19 PM Michael Chan wrote:
> On Sun, 2013-12-01 at 02:34 +0100, Rafael J. Wysocki wrote:
> > From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > 
> > Modify tg3_chip_reset() and tg3_close() to check if the PCI network
> > adapter device is accessible at all in order to skip poking it or
> > trying to handle a carrier loss in vain when that's not the case.
> > Introduce a special PCI helper function pci_device_is_present()
> > for this purpose.
> > 
> > Of course, this uncovers the lack of the appropriate RTNL locking
> > in tg3_suspend() and tg3_resume(), so add that locking in there
> > too.
> > 
> > These changes prevent tg3 from burning a CPU at 100% load level for
> > solid several seconds after the Thunderbolt link is disconnected from
> > a Matrox DS1 docking station. 
> 
> I'm not familiar with the DS1.  Does the tg3 device get removed through
> tg3_remove_one() in this case?

Yes, this is a normal removal except that the device is gone physically when
it happens.

Thunderbolt cable disconnect is like a power failure for all devices on
the link (that is, all devices in the DS1 in this particular case).

> What happens when you reconnect the DS1?

Well, it works.  ACPIPHP just waits for the removal to complete and then it
handles the hot-add event and the device works normally after that.

The only problem is that without the patch the hot-removal takes a few seconds
and quite a lot of CPU power due to the tight loop spinning in tg3_carrier_off()
called by tg3_close(), while with the patch it just happens almost instantaneously.

And in the Thunderbolt disconnect case doing the entire tg3_chip_reset() is
pointless anyway, because the config space of the device is not available then.

Thanks!

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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