On 28.09.21 09:24, Oleksandr Andrushchenko wrote: > > 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 >>>>>>>>>>> >>>>>>>>>>> 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 >>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>>> --- >>>>>>>>>>> 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 Yes, that's fine. Juergen