Re: [PATCH] virtio: kconfig: memory devices are PCI only

[David Hildenbrand]

On 06.09.24 10:18, Paolo Bonzini wrote:
> On Fri, Sep 6, 2024 at 9:40 AM David Hildenbrand <david@redhat.com> wrote:
> > On 06.09.24 09:37, Paolo Bonzini wrote:
> > > Virtio memory devices rely on PCI BARs to expose the contents of memory.
> > > Because of this they cannot be used with virtio-mmio or virtio-ccw.  In fact
> >
> > Guess what I am working on at this very the moment ;)
>
> Ok, then hardcoding VIRTIO_PCI is not nice.
>
> > > @@ -45,7 +46,7 @@ config VIRTIO_PMEM_SUPPORTED
> > >    config VIRTIO_PMEM
> > >        bool
> > >        default y
> > > -    depends on VIRTIO
> > > +    depends on VIRTIO_PCI
> >
> > depends on VIRTIO_MD ?
>
> No, because VIRTIO_MD is "default n" (and anyway you don't want to
> enable it by hand in the --without-default-devices case).

Right, that's what I originally tried to achieve.

> But something like this could be a good alternative if you plan to
> support virtio-ccw as well:
>
> diff --git a/hw/virtio/Kconfig b/hw/virtio/Kconfig
> index aa63ff7fd41..253e7d3f90a 100644
> --- a/hw/virtio/Kconfig
> +++ b/hw/virtio/Kconfig
> @@ -16,6 +16,7 @@ config VIRTIO_PCI
>       default y if PCI_DEVICES
>       depends on PCI
>       select VIRTIO
> +    select VIRTIO_MD_SUPPORTED
>
>   config VIRTIO_MMIO
>       bool
> @@ -35,8 +36,14 @@ config VIRTIO_CRYPTO
>       default y
>       depends on VIRTIO
>
> +# not all virtio transports support memory devices; if none does,
> +# no need to include the code
> +config VIRTIO_MD_SUPPORTED
> +    bool
> +
>   config VIRTIO_MD
>       bool
> +    depends on VIRTIO_MD_SUPPORTED
>       select MEM_DEVICE
>
>   config VIRTIO_PMEM_SUPPORTED
> @@ -46,6 +51,7 @@ config VIRTIO_PMEM
>       bool
>       default y
>       depends on VIRTIO
> +    depends on VIRTIO_MD_SUPPORTED
>       depends on VIRTIO_PMEM_SUPPORTED
>       select VIRTIO_MD
>
> @@ -57,6 +63,7 @@ config VIRTIO_MEM
>       default y
>       depends on VIRTIO
>       depends on LINUX
> +    depends on VIRTIO_MD_SUPPORTED
>       depends on VIRTIO_MEM_SUPPORTED
>       select VIRTIO_MD
>
>
> and then you just need to select VIRTIO_MD_SUPPORTED from VIRTIO_CCW.

Sounds good.

> In the case of PCI there is some board support code as well, which is
> why VIRTIO_{MEM,PMEM}_SUPPORTED is selected from "config PC", but
> perhaps in the s390 code you can select those three from VIRTIO_CCW as
> well.

Yes, only VIRTIO_MEM_SUPPORTED for now.

> If this looks good I'll send it as v2.


Thanks!

--
Cheers,

David / dhildenb