Messages in this thread | | | Date | Wed, 9 Jul 2014 15:26:05 +0100 | From | David Vrabel <> | Subject | Re: [PATCH v3 4/7] xen/pciback: Implement PCI reset slot or bus with 'do_flr' SysFS attribute |
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On 09/07/14 15:12, Konrad Rzeszutek Wilk wrote: > On Wed, Jul 09, 2014 at 01:32:10PM +0100, David Vrabel wrote: >> On 08/07/14 19:46, Konrad Rzeszutek Wilk wrote: >>> On Tue, Jul 08, 2014 at 07:02:51PM +0100, David Vrabel wrote: >>>> On 08/07/14 19:58, konrad@kernel.org wrote: >>>>> --- a/Documentation/ABI/testing/sysfs-driver-pciback >>>>> +++ b/Documentation/ABI/testing/sysfs-driver-pciback >>>>> @@ -82,3 +82,14 @@ Description: >>>>> device is shared, enabled, or on a level interrupt line. >>>>> Writing a string of DDDD:BB:DD.F will toggle the state. >>>>> This is Domain:Bus:Device.Function where domain is optional. >>>>> + >>>>> +What: /sys/bus/pci/drivers/pciback/do_flr >>>>> +Date: July 2014 >>>>> +KernelVersion: 3.16 >>>>> +Contact: xen-devel@lists.xenproject.org >>>>> +Description: >>>>> + An option to slot or bus reset an PCI device owned by >>>>> + Xen PCI backend. Writing a string of DDDD:BB:DD.F will cause >>>>> + the driver to perform an slot or bus reset if the device >>>>> + supports. It also checks to make sure that all of the devices >>>>> + under the bridge are owned by Xen PCI backend. >>>> >>>> Not sure I like this new interface. I solved this by adding a new reset >>>> file that looked like the regular one the pci would have if it supported >>>> FLR. I'm fairly sure I posted a series for this. Was there a reason >>>> you didn't do this? >>> >>> It did not work. >>> >>> During bootup kobject would complain about a secondary 'reset' SysFS >>> on the PCI device. >> >> I think this because of pciback registering a driver too early, before >> the device is fully initialized. You can see in the trace that it is >> the common pci code that is trying to add the "reset" file so it must be >> doing this /after/ pciback's probe has been called. >> >> I would consider: >> >> 1. Removing the "hide" module parameter -- it doesn't work if pciback is >> a module anyway. > > I find it incredibly useful and so do a lot of other people.
PCI passthrough must work well without hide and without pciback being built-in (and it does with the "reset" change).
What are you using "hide" for?
>> 2. Making pciback initialize like a regular driver module (no >> fs_initcall() shenanigans). > > The point is to take the PCI device before the drivers touch it. > > We want it to be in a pristine state so that the device driver > domains can use it.
But hide only ensures this the first time the device is assigned. Using a function reset ensures this all the time.
>> 3. Require userspace to sort out binding the device to pciback (e.g., >> libxl already does the unbind if requested). > > How would you do the bus/slot reset? Or are you thinking that at > that point the 'reset' functionality would be over-written to point > to Xen pciback and it would do the job?
I'm not sure I understand your question. libxl already does the function reset (by writing to "reset").
>> 4. Finally, I would consider generic driver core functionality for >> prioritizing drivers so they get probed first. > > Not sure I understand why you want the drivers to use the device > first? The point is that we can 'hide' them from the generic > drivers and present them to the backend domains.
The pciback driver would be prioritized, so it would be probed first.
> Regardless of these - I am curious to why you don't like do_flr > as it is even implemented in the the toolstack (but buggy) and > it does a good job of allowing us to do slot/bus reset?
Because there is already a documented interface for resetting devices (the "reset" file), we don't want a second interface.
David
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