linux-kernel - Re: [BUGFIX 3/4] PCI/PM: Fix config reg access for D3cold and bridge suspending

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Message-ID: <Pine.LNX.4.44L0.1208031042580.1520-100000@iolanthe.rowland.org>
Date:	Fri, 3 Aug 2012 10:46:20 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Huang Ying <ying.huang@...el.com>
cc:	Bjorn Helgaas <bhelgaas@...gle.com>,
	<linux-kernel@...r.kernel.org>, <linux-pci@...r.kernel.org>,
	<linux-pm@...r.kernel.org>, "Rafael J. Wysocki" <rjw@...k.pl>
Subject: Re: [BUGFIX 3/4] PCI/PM: Fix config reg access for D3cold and bridge
 suspending

On Fri, 3 Aug 2012, Huang Ying wrote:

> This patch fixes the following bug:
> 
> http://marc.info/?l=linux-pci&m=134338059022620&w=2
> 
> Where lspci does not work properly if a device and the corresponding
> parent bridge (such as PCIe port) is suspended.  This is because the
> device configuration space registers will be not accessible if the
> corresponding parent bridge is suspended or the device is put into
> D3cold state.
> 
> To solve the issue, the bridge/PCIe port connected to the device is
> put into active state before read/write configuration space registers.
> If the device is in D3cold state, it will be put into active state
> too.
> 
> To avoid resume/suspend PCIe port for each configuration register
> read/write, a small delay is added before the PCIe port to go
> suspended.


> +static void
> +pci_config_pm_runtime_put(struct pci_dev *pdev)
> +{
> +	struct device *dev = &pdev->dev;
> +	struct device *parent = dev->parent;
> +
> +	pm_runtime_put(dev);
> +	if (parent)
> +		pm_runtime_put(parent);
> +}

This is just the sort of thing Rafael and I have been talking about.  
Why do an asynchronous put, going to all the trouble of using the 
workqueue, if the idle routine is just going to call 
pm_schedule_suspend()?

Why not call pm_runtime_put_sync() instead?

Alan Stern

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