linux-kernel - Re: [Xen-devel] [PATCH v5 9/9] xen/pciback: Implement PCI reset slot or bus with 'do

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Date:	Thu, 4 Dec 2014 14:10:54 +0100
From:	Sander Eikelenboom <linux@...elenboom.it>
To:	David Vrabel <david.vrabel@...rix.com>
CC:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	bhelgaas@...gle.com, <linux-pci@...r.kernel.org>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	<linux-kernel@...r.kernel.org>, <xen-devel@...ts.xenproject.org>
Subject: Re: [Xen-devel] [PATCH v5 9/9] xen/pciback: Implement PCI reset slot or bus with 'do_flr' SysFS attribute


Thursday, December 4, 2014, 1:24:47 PM, you wrote:

> On 04/12/14 12:06, Konrad Rzeszutek Wilk wrote:
>> 
>> On Dec 4, 2014 6:30 AM, David Vrabel <david.vrabel@...rix.com> wrote:
>>>
>>> On 03/12/14 21:40, Konrad Rzeszutek Wilk wrote: 
>>>>
>>>> Instead of doing all this complex dance, we depend on the toolstack 
>>>> doing the right thing. As such implement the 'do_flr' SysFS attribute 
>>>> which 'xl' uses when a device is detached or attached from/to a guest. 
>>>> It bypasses the need to worry about the PCI lock. 
>>>
>>> No.  Get pciback to add its own "reset" sysfs file (as I have repeatedly 
>>> proposed). 
>>>
>> 
>> Which does not work as the kobj will complain (as there is already an 'reset' associated with the PCI device).

> It is only needed if the core won't provide one.

> +static int pcistub_try_create_reset_file(struct pci_dev *pci)
> +{
> +       struct xen_pcibk_dev_data *dev_data = pci_get_drvdata(pci);
> +       struct device *dev = &pci->dev;
> +       int ret;
> +
> +       /* Already have a per-function reset? */
> +       if (pci_probe_reset_function(pci) == 0)
> +               return 0;
> +
> +       ret = device_create_file(dev, &dev_attr_reset);
> +       if (ret < 0)
> +               return ret;
+       dev_data->>created_reset_file = true;
> +       return 0;
> +}

Wouldn't the "core-reset-sysfs-file" be still wired to the end up calling 
"pci.c:__pci_dev_reset" ?

The problem with that function is that from my testing it seems that the 
first option "pci_dev_specific_reset" always seems to return succes, so all the
other options are skipped (flr, pm, slot, bus). However the device it self is 
not properly reset enough (perhaps the pci_dev_specific_reset is good enough for 
none virtualization purposes and it's probably the least intrusive. For 
virtualization however it would be nice to be sure it resets properly, or have a 
way to force a specific reset routine.) 

So it's the ordering and skipping of the other resets that seems to make
this workaround necessary in the first place.

> David





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