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

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Date:   Fri, 7 Apr 2017 09:36:31 -0700 (PDT)
From:   Stefano Stabellini <sstabellini@...nel.org>
To:     Oleksandr Andrushchenko <andr2000@...il.com>
cc:     Julien Grall <julien.grall@....com>,
        xen-devel@...ts.xenproject.org, joculator@...il.com,
        al1img@...il.com, vlad.babchuk@...il.com, andrii.anisov@...il.com,
        olekstysh@...il.com, konrad.wilk@...cle.com, lars.kurth@...rix.com,
        sstabellini@...nel.org, linux-kernel@...r.kernel.org,
        Oleksandr Andrushchenko <oleksandr_andrushchenko@...m.com>,
        Oleksandr Grytsov <oleksandr_grytsov@...m.com>
Subject: Re: [For Linux 4/4] xen/displif: add ABI for para-virtual display

On Fri, 7 Apr 2017, Oleksandr Andrushchenko wrote:
> 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

It is already defined in include/xen/page.h


> > > +#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
>