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

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Date:   Fri, 7 Apr 2017 17:02:11 +0300
From:   Oleksandr Andrushchenko <andr2000@...il.com>
To:     Julien Grall <julien.grall@....com>, xen-devel@...ts.xenproject.org
Cc:     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

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