Date: Thu, 4 Dec 2014 15:09:09 +0100
From: Sander Eikelenboom <linux@eikelenboom.it>
Organization: Eikelenboom IT services
Message-ID: <308719815.20141204150909@eikelenboom.it>
To: David Vrabel <david.vrabel@citrix.com>
CC: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>, bhelgaas@google.com,
        <linux-pci@vger.kernel.org>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        <linux-kernel@vger.kernel.org>, <xen-devel@lists.xenproject.org>
Subject: Re: [Xen-devel] [PATCH v5 9/9] xen/pciback: Implement PCI reset slot or bus with 'do_flr' SysFS attribute
In-Reply-To: <548064EA.8090905@citrix.com>
References: <201412041206.sB4C6XVQ009497@userz7022.oracle.com> <5480528F.8010106@citrix.com> <1107877503.20141204141054@eikelenboom.it> <548064EA.8090905@citrix.com>
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Sender: linux-kernel-owner@vger.kernel.org


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@citrix.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. 

vfio-pci has:
- logic to do the try-slot-bus-reset logic
- it has quirks specific to vga passthrough
implemented in from the looks of it a quite clean driver.
(the main issue with it so far was you could only seize devices based on 
vendor and device id, which can be a problem when you have multiple devices.
However that was resolved recently if i am correct.)

And neither of those will be supported by xen-pciback if i get your message 
right ?

--
Sander

> David


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