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

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Message-ID: <5480702F.2060004@citrix.com>
Date:	Thu, 4 Dec 2014 14:31:11 +0000
From:	David Vrabel <david.vrabel@...rix.com>
To:	Sander Eikelenboom <linux@...elenboom.it>
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

On 04/12/14 14:09, Sander Eikelenboom wrote:
> 
> Thursday, December 4, 2014, 2:43:06 PM, you wrote:
> 
>> On 04/12/14 13:10, Sander Eikelenboom wrote:
>>>
>>> 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.)
> 
>> Then you need work with the maintainer for those specific devices or
>> drivers to fix their specific reset function.
> 
>> I'm not adding stuff to pciback to workaround broken quirks.
> 
> OK that's a pretty clear message there, so if one wants to use pci and vga
> passthrough one should better use KVM and vfio-pci.

Have you (or anyone else) ever raised the problem with the broken reset
quirk for certain devices with the relevant maintainer?

> vfio-pci has:
> - logic to do the try-slot-bus-reset logic

Just because vfio-pci fixed it incorrectly doesn't mean pciback has to
as well.

It makes no sense for both pciback and vfio-pci to workaround problems
with pci_function_reset() in different ways -- it should be fixed in the
core PCI code so both can benefit and make use of the same code.

David

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