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

["Jürgen Groß" <jgross@suse.com>]

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@epam.com>
>>>
>>> 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@epam.com>
>>> ---
>>>    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