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

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Message-ID: <alpine.DEB.2.10.1704071050020.2759@sstabellini-ThinkPad-X260>
Date:   Fri, 7 Apr 2017 10:50:42 -0700 (PDT)
From:   Stefano Stabellini <sstabellini@...nel.org>
To:     Oleksandr Andrushchenko <andr2000@...il.com>
cc:     Stefano Stabellini <sstabellini@...nel.org>,
        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,
        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:
> On 04/07/2017 07:36 PM, Stefano Stabellini wrote:
> > 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
> Thank you, Stefano, but I meant if the change below
> will fit the requirement, e.g. what Julien means is:
> -#define XENDISPL_EVENT_PAGE_SIZE 4096
> +#define XENDISPL_EVENT_PAGE_SIZE XEN_PAGE_SIZE
> Julien, does this change work for you?

Sure, I think that would be OK. Also using XEN_PAGE_SIZE directly would
be OK.


> > > > > +#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
> > > 
> Thank you,
> Oleksandr
>