Messages in this thread | | | Subject | Re: [PATCH v4 1/2] xen-pciback: prepare for the split for stub and PV | From | Juergen Gross <> | Date | Tue, 28 Sep 2021 08:59:07 +0200 |
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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@epam.com> >>>>>>> >>>>>>> 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@epam.com> >>>>>>> >>>>>>> --- >>>>>>> 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.
Juergen
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