[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH v4 1/2] xen-pciback: prepare for the split for stub and PV
On 28.09.21 10:20, Juergen Gross wrote: > On 28.09.21 09:17, Oleksandr Andrushchenko wrote: >> >> On 28.09.21 09:59, Juergen Gross wrote: >>> On 28.09.21 08:56, Oleksandr Andrushchenko wrote: >>>> >>>> On 28.09.21 09:42, Jan Beulich wrote: >>>>> On 28.09.2021 06:18, Stefano Stabellini wrote: >>>>>> On Mon, 27 Sep 2021, Juergen Gross wrote: >>>>>>> On 27.09.21 09:35, Oleksandr Andrushchenko wrote: >>>>>>>> On 27.09.21 10:26, Jan Beulich wrote: >>>>>>>>> On 27.09.2021 08:58, Oleksandr Andrushchenko wrote: >>>>>>>>>> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx> >>>>>>>>>> >>>>>>>>>> Currently PCI backend implements multiple functionalities at a time. >>>>>>>>>> To name a few: >>>>>>>>>> 1. It is used as a database for assignable PCI devices, e.g. xl >>>>>>>>>> pci-assignable-{add|remove|list} manipulates that list. So, >>>>>>>>>> whenever >>>>>>>>>> the toolstack needs to know which PCI devices can be passed >>>>>>>>>> through >>>>>>>>>> it reads that from the relevant sysfs entries of the pciback. >>>>>>>>>> 2. It is used to hold the unbound PCI devices list, e.g. when passing >>>>>>>>>> through a PCI device it needs to be unbound from the relevant >>>>>>>>>> device >>>>>>>>>> driver and bound to pciback (strictly speaking it is not >>>>>>>>>> required >>>>>>>>>> that the device is bound to pciback, but pciback is again >>>>>>>>>> used as a >>>>>>>>>> database of the passed through PCI devices, so we can >>>>>>>>>> re-bind the >>>>>>>>>> devices back to their original drivers when guest domain >>>>>>>>>> shuts >>>>>>>>>> down) >>>>>>>>>> 3. Device reset for the devices being passed through >>>>>>>>>> 4. Para-virtualised use-cases support >>>>>>>>>> >>>>>>>>>> The para-virtualised part of the driver is not always needed as some >>>>>>>>>> architectures, e.g. Arm or x86 PVH Dom0, are not using >>>>>>>>>> backend-frontend >>>>>>>>>> model for PCI device passthrough. For such use-cases make the very >>>>>>>>>> first step in splitting the xen-pciback driver into two parts: Xen >>>>>>>>>> PCI stub and PCI PV backend drivers. >>>>>>>>>> >>>>>>>>>> Signed-off-by: Oleksandr Andrushchenko >>>>>>>>>> <oleksandr_andrushchenko@xxxxxxxx> >>>>>>>>>> >>>>>>>>>> --- >>>>>>>>>> Changes since v3: >>>>>>>>>> - Move CONFIG_XEN_PCIDEV_STUB to the second patch >>>>>>>>> I'm afraid this wasn't fully done: >>>>>>>>> >>>>>>>>>> --- a/drivers/xen/xen-pciback/Makefile >>>>>>>>>> +++ b/drivers/xen/xen-pciback/Makefile >>>>>>>>>> @@ -1,5 +1,6 @@ >>>>>>>>>> # SPDX-License-Identifier: GPL-2.0 >>>>>>>>>> obj-$(CONFIG_XEN_PCIDEV_BACKEND) += xen-pciback.o >>>>>>>>>> +obj-$(CONFIG_XEN_PCIDEV_STUB) += xen-pciback.o >>>>>>>>> While benign when added here, this addition still doesn't seem to >>>>>>>>> belong here. >>>>>>>> My bad. So, it seems without CONFIG_XEN_PCIDEV_STUB the change seems >>>>>>>> >>>>>>>> to be non-functional. With CONFIG_XEN_PCIDEV_STUB we fail to build on >>>>>>>> 32-bit >>>>>>>> >>>>>>>> architectures... >>>>>>>> >>>>>>>> What would be the preference here? Stefano suggested that we still >>>>>>>> define >>>>>>>> >>>>>>>> CONFIG_XEN_PCIDEV_STUB, but in disabled state, e.g. we add tristate to >>>>>>>> it >>>>>>>> >>>>>>>> in the second patch >>>>>>>> >>>>>>>> Another option is just to squash the two patches. >>>>>>> Squashing would be fine for me. >>>>>> It is fine for me to squash the two patches. >>>>>> >>>>>> But in any case, wouldn't it be better to modify that specific change to: >>>>>> >>>>>> diff --git a/drivers/xen/xen-pciback/Makefile >>>>>> b/drivers/xen/xen-pciback/Makefile >>>>>> index e2cb376444a6..e23c758b85ae 100644 >>>>>> --- a/drivers/xen/xen-pciback/Makefile >>>>>> +++ b/drivers/xen/xen-pciback/Makefile >>>>>> @@ -1,6 +1,5 @@ >>>>>> # SPDX-License-Identifier: GPL-2.0 >>>>>> -obj-$(CONFIG_XEN_PCIDEV_BACKEND) += xen-pciback.o >>>>>> -obj-$(CONFIG_XEN_PCIDEV_STUB) += xen-pciback.o >>>>>> +obj-$(CONFIG_XEN_PCI_STUB) += xen-pciback.o >>>>> But that wouldn't allow the driver to be a module anymore, would it? >>>> >>>> Exactly. I forgot that when playing with module/built-in I was not able >>>> >>>> to control that anymore because CONFIG_XEN_PCI_STUB will always be >>>> >>>> in "y" state, thus even if you have CONFIG_XEN_PCIDEV_BACKEND=m >>>> >>>> you won't be able to build it as module. So, I will probably put a comment >>>> >>>> about that in the Makefile explaining the need for >>>> >>>> obj-$(CONFIG_XEN_PCIDEV_BACKEND) += xen-pciback.o >>>> obj-$(CONFIG_XEN_PCIDEV_STUB) += xen-pciback.o >>> >>> In case the real split between both parts of xen-pciback is done this >>> will be needed anyway. >> >> Yes, it will >> >> So, I'll put a comment in the Makefile: >> >> # N.B. This cannot be expressed with a single line using CONFIG_XEN_PCI_STUB >> >> # as it always remains in "y" state, thus preventing the driver to be built >> as >> >> # a module. >> >> obj-$(CONFIG_XEN_PCIDEV_BACKEND) += xen-pciback.o >> obj-$(CONFIG_XEN_PCIDEV_STUB) += xen-pciback.o >> >> Will this be ok or needs some re-wording? > > I'd add that CONFIG_XEN_PCIDEV_BACKEND and CONFIG_XEN_PCIDEV_STUB are > mutually exclusive. # N.B. The below cannot be expressed with a single line using # CONFIG_XEN_PCI_STUB as it always remains in "y" state, # thus preventing the driver to be built as a module. # Please note, that CONFIG_XEN_PCIDEV_BACKEND and # CONFIG_XEN_PCIDEV_STUB are mutually exclusive. obj-$(CONFIG_XEN_PCIDEV_BACKEND) += xen-pciback.o obj-$(CONFIG_XEN_PCIDEV_STUB) += xen-pciback.o > > > Juergen Thank you, Oleksandr
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