Re: [PATCH 1/2] xen/displif: Protocol version 2

[Jürgen Groß <jgross@xxxxxxxx>]

On 30.06.20 08:13, Oleksandr Andrushchenko wrote:
> On 6/29/20 10:02 AM, Jürgen Groß wrote:
> > On 20.05.20 11:04, Oleksandr Andrushchenko wrote:
> > > From: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
> > >
> > > 1. Change protocol version from string to integer
> > >
> > > Version string, which is in fact an integer, is hard to handle in the
> > > code that supports different protocol versions. To simplify that
> > > make the version an integer.
> > >
> > > 2. Pass buffer offset with XENDISPL_OP_DBUF_CREATE
> > >
> > > There are cases when display data buffer is created with non-zero
> > > offset to the data start. Handle such cases and provide that offset
> > > while creating a display buffer.
> > >
> > > 3. Add XENDISPL_OP_GET_EDID command
> > >
> > > Add an optional request for reading Extended Display Identification
> > > Data (EDID) structure which allows better configuration of the
> > > display connectors over the configuration set in XenStore.
> > > With this change connectors may have multiple resolutions defined
> > > with respect to detailed timing definitions and additional properties
> > > normally provided by displays.
> > >
> > > If this request is not supported by the backend then visible area
> > > is defined by the relevant XenStore's "resolution" property.
> > >
> > > If backend provides extended display identification data (EDID) with
> > > XENDISPL_OP_GET_EDID request then EDID values must take precedence
> > > over the resolutions defined in XenStore.
> > >
> > > 4. Bump protocol version to 2.
> > >
> > > Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
> > > ---
> > >    xen/include/public/io/displif.h | 83 +++++++++++++++++++++++++++++++--
> > >    1 file changed, 80 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/xen/include/public/io/displif.h b/xen/include/public/io/displif.h
> > > index cc5de9cb1f35..4d43ba5078c8 100644
> > > --- a/xen/include/public/io/displif.h
> > > +++ b/xen/include/public/io/displif.h
> > > @@ -38,7 +38,7 @@
> > >     *                           Protocol version
> > > ******************************************************************************
> > >     */
> > > -#define XENDISPL_PROTOCOL_VERSION     "1"
> > > +#define XENDISPL_PROTOCOL_VERSION     2
> > This is not very nice regarding compatibility.
> >
> > Can't you add a new macro for the integer value?
> We can leave it as is, e.g. define XENDISPL_PROTOCOL_VERSION as "2",
>
> so we do not break the existing users. Then if every user of the header has
>
> its local copy (this is what we now use in the display backend), then that
> local copy can be changed in a way suitable for the concrete user, e.g. "2"
>
> redefined to 2. This cannot be done (?) for the Linux Kernel though.
>
> Or we can have
>
> #define XENDISPL_PROTOCOL_VERSION     "2"
>
> #define XENDISPL_PROTOCOL_VERSION_INT  2
>
> Jurgen, what's your preference here?
I would prefer the latter, as it avoids the need to modify the header
when copying it to a local project.


Juergen