Re: [PATCH v5 7/7] RFC: add initial support for configuring feature bits

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, May 18, 2022 at 06:31:18PM +0300, Max Gurtovoy wrote:
> 
> On 5/15/2022 5:38 PM, Michael S. Tsirkin wrote:
> > On Wed, Apr 27, 2022 at 01:58:24AM +0300, Max Gurtovoy wrote:
> > > After adding the concept of a management and a managed device, add
> > > another example of using this concept to manage resources.
> > > 
> > > Today there is no standard definition in the spec that allows user to
> > > setup specific feature bits of a virtio device.
> > > 
> > > For that, extend the management mechanism to allow management devices to
> > > change feature bits of its managed devices.
> > > 
> > > Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
> > 
> > Please, add more explanation here. E.g. I am guessing these are
> > host feature bits, right? How does driver know which features are
> > ok to enable?
> > 
> > I would expect some description sections and conformance sections.
> > 
> This is an RFC to emphasize the need for the admin command set.
> 
> I added this because we agreed to think on more features for showing the
> motivation of this mechanism.
> 
> I can work on MSI-X or feature bits as initial submission.
> 
> Choose what do you think will be easier to merge and lets keep working on
> it.
> 
> Working on both will cause distraction.

OK.

I personally think feature bits are easier, we don't need to also refer
to the pci spec.

> > > ---
> > >   admin.tex | 12 +++++++++---
> > >   1 file changed, 9 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/admin.tex b/admin.tex
> > > index 5b54743..43106ba 100644
> > > --- a/admin.tex
> > > +++ b/admin.tex
> > > @@ -113,7 +113,9 @@ \subsection{VIRTIO ADMIN DEVICE CAPS IDENTIFY command}\label{sec:Basic Facilitie
> > >           * Bit 0 - if set, the device is a management device
> > >           * Bit 1 - if set, the device is a type 1 management device that supports
> > >           *         MSI-X vector mgmt of its type 1 managed devices
> > > -        * Bits 2 - 63 - reserved for future capabilities.
> > > +        * Bit 2 - if set, the device is a type 1 management device that supports
> > > +        *         feature mgmt of bits 0 to 63 for its type 1 managed devices
> > > +        * Bits 3 - 63 - reserved for future capabilities.
> > >           */
> > >          le64 device_admin_caps;
> > >          u8 reserved[112];
> > > @@ -143,7 +145,9 @@ \subsection{VIRTIO ADMIN DEVICE CAPS ACCEPT command}\label{sec:Basic Facilities
> > >           * Bit 0 - if set, the driver accepted the device as a management device
> > >           * Bit 1 - if set, the driver accepted the device as a type 1 management device
> > >           *         that supports MSI-X vector mgmt of its type 1 managed devices
> > > -        * Bits 2 - 63 - reserved for future capabilities.
> > > +        * Bit 2 - if set, the driver accepted the device as a type 1 management device
> > > +        *         that supports feature mgmt of bits 0 to 63 for its type 1 managed devices
> > > +        * Bits 3 - 63 - reserved for future capabilities.
> > >           */
> > >          le64 driver_admin_caps;
> > >          u8 reserved[112];
> > > @@ -167,12 +171,14 @@ \subsection{VIRTIO ADMIN DEVICE MGMT command}\label{sec:Basic Facilities of a Vi
> > >           u8 operation;
> > >           /*
> > >            * 0 - MSI-X vector
> > > -         * 1 - 65535 are reserved
> > > +         * 1 - Device feature bits 0 to 63
> > > +         * 2 - 65535 are reserved
> > >            */
> > >           le16 resource;
> > >           /*
> > >            * The value to the given resource:
> > >            * if resource = 0 (MSI-X vector), it's a 1-based count.
> > > +         * if resource = 1 (Device feature bits 0 to 63), it's a feature bitmap.
> > >            */
> > >           le64 resource_val;
> > >           u8 reserved[5];
> > > -- 
> > > 2.21.0