[RFC,0/2] virtio-ccw: allow to disable legacy virtio

Message

Cornelia Huck March 4, 2021, 1:27 p.m. UTC

Unlike virtio-pci, virtio-ccw is currently always a transitional
driver (i.e. it always includes support for legacy devices.) The
differences between legacy and virtio-1+ virtio-ccw devices are not
that big (the most interesting things are in common virtio code
anyway.)

It might be beneficial to make support for legacy virtio generally
configurable, in case we want to remove it completely in a future
where we all have flying cars. As a prereq, we need to make it
configurable for virtio-ccw.

Patch 1 introduces a parameter; now that I look at it, it's probably
not that useful (not even for testing), so I'm inclined to drop it
again.

Patch 2 adds a new config symbol for generic legacy virtio support,
which currently does not do anything but being selected by the
legacy options for virtio-pci and virtio-ccw. A virtio-ccw driver
without legacy support will require a revision of 1 or higher to
be supported by the device.

A virtio-ccw driver with legacy turned off works well for me with
transitional devices and fails onlining gracefully for legacy devices
(max_revision=0 in QEMU).

(I also have some code that allows to make devices non-transitional
in QEMU, but I haven't yet found time to polish the patches.)

Cornelia Huck (2):
  virtio/s390: add parameter for minimum revision
  virtio/s390: make legacy support configurable

 arch/s390/Kconfig                       |  11 ++
 drivers/s390/virtio/Makefile            |   1 +
 drivers/s390/virtio/virtio_ccw.c        | 179 ++++++++----------------
 drivers/s390/virtio/virtio_ccw_common.h | 113 +++++++++++++++
 drivers/s390/virtio/virtio_ccw_legacy.c | 138 ++++++++++++++++++
 drivers/virtio/Kconfig                  |   8 ++
 6 files changed, 330 insertions(+), 120 deletions(-)
 create mode 100644 drivers/s390/virtio/virtio_ccw_common.h
 create mode 100644 drivers/s390/virtio/virtio_ccw_legacy.c


base-commit: cf6acb8bdb1d829b85a4daa2944bf9e71c93f4b9

Comments

Cornelia Huck May 26, 2021, 2:34 p.m. UTC | #1

On Thu,  4 Mar 2021 14:27:13 +0100
Cornelia Huck <[e-mail]> wrote:

Just found this old series sitting there... does anyone have an opinion
on the general approach?

> Unlike virtio-pci, virtio-ccw is currently always a transitional
> driver (i.e. it always includes support for legacy devices.) The
> differences between legacy and virtio-1+ virtio-ccw devices are not
> that big (the most interesting things are in common virtio code
> anyway.)
> 
> It might be beneficial to make support for legacy virtio generally
> configurable, in case we want to remove it completely in a future
> where we all have flying cars. As a prereq, we need to make it
> configurable for virtio-ccw.
> 
> Patch 1 introduces a parameter; now that I look at it, it's probably
> not that useful (not even for testing), so I'm inclined to drop it
> again.
> 
> Patch 2 adds a new config symbol for generic legacy virtio support,
> which currently does not do anything but being selected by the
> legacy options for virtio-pci and virtio-ccw. A virtio-ccw driver
> without legacy support will require a revision of 1 or higher to
> be supported by the device.
> 
> A virtio-ccw driver with legacy turned off works well for me with
> transitional devices and fails onlining gracefully for legacy devices
> (max_revision=0 in QEMU).
> 
> (I also have some code that allows to make devices non-transitional
> in QEMU, but I haven't yet found time to polish the patches.)
> 
> Cornelia Huck (2):
>   virtio/s390: add parameter for minimum revision
>   virtio/s390: make legacy support configurable
> 
>  arch/s390/Kconfig                       |  11 ++
>  drivers/s390/virtio/Makefile            |   1 +
>  drivers/s390/virtio/virtio_ccw.c        | 179 ++++++++----------------
>  drivers/s390/virtio/virtio_ccw_common.h | 113 +++++++++++++++
>  drivers/s390/virtio/virtio_ccw_legacy.c | 138 ++++++++++++++++++
>  drivers/virtio/Kconfig                  |   8 ++
>  6 files changed, 330 insertions(+), 120 deletions(-)
>  create mode 100644 drivers/s390/virtio/virtio_ccw_common.h
>  create mode 100644 drivers/s390/virtio/virtio_ccw_legacy.c
> 
> 
> base-commit: cf6acb8bdb1d829b85a4daa2944bf9e71c93f4b9