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Subject: Re: [For Linux 4/4] xen/displif: add ABI for para-virtual display
To: Oleksandr Andrushchenko <andr2000@gmail.com>,
        Julien Grall <julien.grall@arm.com>, xen-devel@lists.xenproject.org
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 <82ade2ce-93e0-d817-b289-ca09fa1bb66e@arm.com>
 <9ae3da7e-069a-f93c-c1ef-800a46c7e067@gmail.com>
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        Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>,
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From: Juergen Gross <jgross@suse.com>
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Date: Mon, 10 Apr 2017 08:03:51 +0200
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On 07/04/17 16:02, 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
> 
>>> +#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:
>>> + */

I believe you'll send V2 due to the XEN_PAGE_SIZE usage?

Can you then please remove the editor mode settings block in each
header, too? Those are disliked in the Linux tree.


Juergen