Re: [Xen-devel] [PATCH v1 0/2] libxl: add PV display device driver interface

[Oleksandr Grytsov <al1img@xxxxxxxxx>]

On Wed, Apr 5, 2017 at 5:18 PM, Oleksandr Grytsov <al1img@xxxxxxxxx> wrote:
> On Wed, Apr 5, 2017 at 5:00 PM, Konrad Rzeszutek Wilk
> <konrad.wilk@xxxxxxxxxx> wrote:
>> On Wed, Apr 05, 2017 at 02:49:26PM +0100, Ian Jackson wrote:
>>> al1img . writes ("Re: [PATCH v1 0/2] libxl: add PV display device driver 
>>> interface"):
>>> > On Wed, Apr 5, 2017 at 2:05 PM, Ian Jackson <ian.jackson@xxxxxxxxxxxxx> 
>>> > wrote:
>>> > > Sorry to show my ignorance, but what is a "PV display device" ?
>>> > > Where is the backend ?  What protocol do the frontend/backend speak ?
>>> >
>>> > This is PV display device which provides virtual screens for frontends.
>>> > We are working on the backend and frontend. They are currently under
>>> > development.
>>>
>>> Thanks for the reference to
>>>    http://marc.info/?l=xen-devel&m=149137266022490&w=2
>>> which was very helpful.
>>>
>>> I think you should combine this series with that patch.  That patch
>>> will need wider review and ack from Konrad (as our PV interface tsar);
>>
>> Done, as in Reviewed-by and I am going to check it in once my 
>> 'before-staging' tests
>> finish.
>>
>
> I guess it is late to combine the patches as the protocol already acked.
>
>>> AFAICT you're working on that, but I would like to be CC'd on the
>>> mails too.
>>>
>>> > > What are the parameters ?
>>> >
>>> > It has two parameters:
>>> >     * backend - specifies domain where the backend is running;
>>> >     * beAlloc - indicated where display buffers should be allocated
>>> > (see Backend buffer allocation in [3]);
>>>
>>> I don't understand that, I'm afraid.  I guess what I'm missing in this
>>> area is: the guest sees a virtual display device.  But how is this
>>> presented/accessed/named/whatever on the host ?  I would expect to see
>>> some configuraton for this in the libxl idl.
>>>
>
> The display backend is a user-space application which is DRM or Wayland 
> client.
> Generally it can be run on any domain.
>

Negotiation between backend and frontend is done by xen store and
described in the protocol:

+ *--------------------------------- Backend -----------------------------------
+ *
+ * /local/domain/0/backend/vdispl/1/0/frontend-id = "1"
+ * /local/domain/0/backend/vdispl/1/0/frontend =
"/local/domain/1/device/vdispl/0"
+ * /local/domain/0/backend/vdispl/1/0/state = "4"
+ * /local/domain/0/backend/vdispl/1/0/versions = "1,2"
+ *
+ *--------------------------------- Frontend ----------------------------------
+ *
+ * /local/domain/1/device/vdispl/0/backend-id = "0"
+ * /local/domain/1/device/vdispl/0/backend =
"/local/domain/0/backend/vdispl/1/0"
+ * /local/domain/1/device/vdispl/0/state = "4"
+ * /local/domain/1/device/vdispl/0/version = "1"
+ * /local/domain/1/device/vdispl/0/be-alloc = "1"
+ *

libxl handles Backend/Frontend  configuration above. Which is in lib xl idl.
Description of connectors will be set by the backend to the frontend directly.
Because the backend aware of display(s) configuration(s).

+ *-------------------------- Connector 0 configuration ------------------------
+ *
+ * /local/domain/1/device/vdispl/0/0/resolution = "1920x1080"
+ * /local/domain/1/device/vdispl/0/0/req-ring-ref = "2832"
+ * /local/domain/1/device/vdispl/0/0/req-event-channel = "15"
+ * /local/domain/1/device/vdispl/0/0/evt-ring-ref = "387"
+ * /local/domain/1/device/vdispl/0/0/evt-event-channel = "16"
+ *
+ *-------------------------- Connector 1 configuration ------------------------
+ *
+ * /local/domain/1/device/vdispl/0/1/resolution = "800x600"
+ * /local/domain/1/device/vdispl/0/1/req-ring-ref = "2833"
+ * /local/domain/1/device/vdispl/0/1/req-event-channel = "17"
+ * /local/domain/1/device/vdispl/0/1/evt-ring-ref = "388"
+ * /local/domain/1/device/vdispl/0/1/evt-event-channel = "18"

>
>>> Thanks,
>>> Ian.
>>>
>>> _______________________________________________
>>> Xen-devel mailing list
>>> Xen-devel@xxxxxxxxxxxxx
>>> https://lists.xen.org/xen-devel
>
> --
> Best Regards,
> Oleksandr Grytsov.



-- 
Best Regards,
Oleksandr Grytsov.

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