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    SubjectRe: [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@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.

    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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