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

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Message-ID: <b87d169c-8463-f93d-4733-f1c2451be931@gmail.com>
Date:   Fri, 7 Apr 2017 20:51:42 +0300
From:   Oleksandr Andrushchenko <andr2000@...il.com>
To:     Stefano Stabellini <sstabellini@...nel.org>
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,
        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 04/07/2017 08:50 PM, Stefano Stabellini wrote:
> 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.
>
Great, thanks
>>>>>> +#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
>>