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Subject: Re: [For Linux 4/4] xen/displif: add ABI for para-virtual display
To: Julien Grall <julien.grall@arm.com>, xen-devel@lists.xenproject.org
References: <1491553840-5180-1-git-send-email-andr2000@gmail.com>
 <1491553840-5180-5-git-send-email-andr2000@gmail.com>
 <82ade2ce-93e0-d817-b289-ca09fa1bb66e@arm.com>
Cc: joculator@gmail.com, al1img@gmail.com, vlad.babchuk@gmail.com,
        andrii.anisov@gmail.com, olekstysh@gmail.com, konrad.wilk@oracle.com,
        lars.kurth@citrix.com, sstabellini@kernel.org,
        linux-kernel@vger.kernel.org,
        Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>,
        Oleksandr Grytsov <oleksandr_grytsov@epam.com>
From: Oleksandr Andrushchenko <andr2000@gmail.com>
Message-ID: <9ae3da7e-069a-f93c-c1ef-800a46c7e067@gmail.com>
Date: Fri, 7 Apr 2017 17:02:11 +0300
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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