Re: [For Linux 4/4] xen/displif: add ABI for para-virtual display

[Oleksandr Andrushchenko]

Hi, Julien!

On 04/07/2017 04:50 PM, Julien Grall wrote:
> Hi Oleksandr,
>
> On 07/04/17 09:30, Oleksandr Andrushchenko wrote:
> > +/*
> > + 
> > ******************************************************************************
> > + *                        Back to front events delivery
> > + 
> > ******************************************************************************
> > + * In order to deliver asynchronous events from back to front a 
> > shared page is
> > + * allocated by front and its granted reference propagated to back via
> > + * XenStore entries (evt-ring-ref/evt-event-channel).
> > + * This page has a common header used by both front and back to 
> > synchronize
> > + * access and control event's ring buffer, while back being a 
> > producer of the
> > + * events and front being a consumer. The rest of the page after the 
> > header
> > + * is used for event packets.
> > + *
> > + * Upon reception of an event(s) front may confirm its reception
> > + * for either each event, group of events or none.
> > + */
> > +
> > +struct xendispl_event_page {
> > +    uint32_t in_cons;
> > +    uint32_t in_prod;
> > +    uint8_t reserved[56];
> > +};
> > +
> > +#define XENDISPL_EVENT_PAGE_SIZE 4096
>
> This will be always the size of a grant (e.g xen page size), right? If 
> so, I would prefer if you use XEN_PAGE_SIZE to so we can easily update 
> Linux in the case Xen is using a different page size.
>
> Note that the Front-end, Backend and Xen may use different page size, 
> so your drivers would need to cope with that. The current approach is 
> to always use the page granularity of Xen.
Will the following satisfy the requirement?
#define XENDISPL_EVENT_PAGE_SIZE XEN_PAGE_SIZE

> > +#define XENDISPL_IN_RING_OFFS (sizeof(struct xendispl_event_page))
> > +#define XENDISPL_IN_RING_SIZE (XENDISPL_EVENT_PAGE_SIZE - 
> > XENDISPL_IN_RING_OFFS)
> > +#define XENDISPL_IN_RING_LEN (XENDISPL_IN_RING_SIZE / sizeof(struct 
> > xendispl_evt))
> > +#define XENDISPL_IN_RING(page) \
> > +    ((struct xendispl_evt *)((char *)(page) + XENDISPL_IN_RING_OFFS))
> > +#define XENDISPL_IN_RING_REF(page, idx) \
> > +    (XENDISPL_IN_RING((page))[(idx) % XENDISPL_IN_RING_LEN])
> > +
> > +#endif /* __XEN_PUBLIC_IO_DISPLIF_H__ */
> > +
> > +/*
> > + * Local variables:
> > + * mode: C
> > + * c-file-style: "BSD"
> > + * c-basic-offset: 4
> > + * tab-width: 4
> > + * indent-tabs-mode: nil
> > + * End:
> > + */
>
> Cheers,
Thank you,
Oleksandr