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Subject: Re: [PATCH v2 3/5] ALSA: xen-front: Implement Xen event channel
 handling
To:     Oleksandr Andrushchenko <andr2000@gmail.com>,
        xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org,
        alsa-devel@alsa-project.org, boris.ostrovsky@oracle.com,
        konrad.wilk@oracle.com, perex@perex.cz, tiwai@suse.com
Cc:     Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
References: <20180416062453.24743-1-andr2000@gmail.com>
 <20180416062453.24743-4-andr2000@gmail.com>
 <f9d307ea-9464-252e-2a5a-11ac0b3163f4@suse.com>
 <2e06f714-ebc2-11bb-078b-8a453ea8464c@gmail.com>
From:   Juergen Gross <jgross@suse.com>
Message-ID: <f41495be-dc72-d58c-5427-714292ab80a0@suse.com>
Date:   Tue, 17 Apr 2018 13:14:50 +0200
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On 17/04/18 10:58, Oleksandr Andrushchenko wrote:
> On 04/16/2018 04:12 PM, Juergen Gross wrote:
>> On 16/04/18 08:24, Oleksandr Andrushchenko wrote:
>>> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
>>>
>>> Handle Xen event channels:
>>>    - create for all configured streams and publish
>>>      corresponding ring references and event channels in Xen store,
>>>      so backend can connect
>>>    - implement event channels interrupt handlers
>>>    - create and destroy event channels with respect to Xen bus state
>>>
>>> Signed-off-by: Oleksandr Andrushchenko
>>> <oleksandr_andrushchenko@epam.com>
>>> ---
>>>   sound/xen/Makefile                |   3 +-
>>>   sound/xen/xen_snd_front.c         |  10 +-
>>>   sound/xen/xen_snd_front.h         |   7 +
>>>   sound/xen/xen_snd_front_evtchnl.c | 474
>>> ++++++++++++++++++++++++++++++++++++++
>>>   sound/xen/xen_snd_front_evtchnl.h |  92 ++++++++
>>>   5 files changed, 584 insertions(+), 2 deletions(-)
>>>   create mode 100644 sound/xen/xen_snd_front_evtchnl.c
>>>   create mode 100644 sound/xen/xen_snd_front_evtchnl.h
>>>
>>> diff --git a/sound/xen/Makefile b/sound/xen/Makefile
>>> index 06705bef61fa..03c669984000 100644
>>> --- a/sound/xen/Makefile
>>> +++ b/sound/xen/Makefile
>>> @@ -1,6 +1,7 @@
>>>   # SPDX-License-Identifier: GPL-2.0 OR MIT
>>>     snd_xen_front-objs := xen_snd_front.o \
>>> -              xen_snd_front_cfg.o
>>> +              xen_snd_front_cfg.o \
>>> +              xen_snd_front_evtchnl.o
>>>     obj-$(CONFIG_SND_XEN_FRONTEND) += snd_xen_front.o
>>> diff --git a/sound/xen/xen_snd_front.c b/sound/xen/xen_snd_front.c
>>> index 65d2494a9d14..eb46bf4070f9 100644
>>> --- a/sound/xen/xen_snd_front.c
>>> +++ b/sound/xen/xen_snd_front.c
>>> @@ -18,9 +18,11 @@
>>>   #include <xen/interface/io/sndif.h>
>>>     #include "xen_snd_front.h"
>>> +#include "xen_snd_front_evtchnl.h"
>> Does it really make sense to have multiple driver-private headers?
>>
>> I think those can be merged.
> I would really like to keep it separate as it clearly
> shows which stuff belongs to which modules.
> At least for me it is easier to maintain it this way.
>>
>>>     static void xen_snd_drv_fini(struct xen_snd_front_info *front_info)
>>>   {
>>> +    xen_snd_front_evtchnl_free_all(front_info);
>>>   }
>>>     static int sndback_initwait(struct xen_snd_front_info *front_info)
>>> @@ -32,7 +34,12 @@ static int sndback_initwait(struct
>>> xen_snd_front_info *front_info)
>>>       if (ret < 0)
>>>           return ret;
>>>   -    return 0;
>>> +    /* create event channels for all streams and publish */
>>> +    ret = xen_snd_front_evtchnl_create_all(front_info, num_streams);
>>> +    if (ret < 0)
>>> +        return ret;
>>> +
>>> +    return xen_snd_front_evtchnl_publish_all(front_info);
>>>   }
>>>     static int sndback_connect(struct xen_snd_front_info *front_info)
>>> @@ -122,6 +129,7 @@ static int xen_drv_probe(struct xenbus_device
>>> *xb_dev,
>>>           return -ENOMEM;
>>>         front_info->xb_dev = xb_dev;
>>> +    spin_lock_init(&front_info->io_lock);
>>>       dev_set_drvdata(&xb_dev->dev, front_info);
>>>         return xenbus_switch_state(xb_dev, XenbusStateInitialising);
>>> diff --git a/sound/xen/xen_snd_front.h b/sound/xen/xen_snd_front.h
>>> index b52226cb30bc..9c2ffbb4e4b8 100644
>>> --- a/sound/xen/xen_snd_front.h
>>> +++ b/sound/xen/xen_snd_front.h
>>> @@ -13,9 +13,16 @@
>>>     #include "xen_snd_front_cfg.h"
>>>   +struct xen_snd_front_evtchnl_pair;
>>> +
>>>   struct xen_snd_front_info {
>>>       struct xenbus_device *xb_dev;
>>>   +    /* serializer for backend IO: request/response */
>>> +    spinlock_t io_lock;
>>> +    int num_evt_pairs;
>>> +    struct xen_snd_front_evtchnl_pair *evt_pairs;
>>> +
>>>       struct xen_front_cfg_card cfg;
>>>   };
>>>   diff --git a/sound/xen/xen_snd_front_evtchnl.c
>>> b/sound/xen/xen_snd_front_evtchnl.c
>>> new file mode 100644
>>> index 000000000000..9ece39f938f8
>>> --- /dev/null
>>> +++ b/sound/xen/xen_snd_front_evtchnl.c
>>> @@ -0,0 +1,474 @@
>>> +// SPDX-License-Identifier: GPL-2.0 OR MIT
>>> +
>>> +/*
>>> + * Xen para-virtual sound device
>>> + *
>>> + * Copyright (C) 2016-2018 EPAM Systems Inc.
>>> + *
>>> + * Author: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
>>> + */
>>> +
>>> +#include <xen/events.h>
>>> +#include <xen/grant_table.h>
>>> +#include <xen/xen.h>
>>> +#include <xen/xenbus.h>
>>> +
>>> +#include "xen_snd_front.h"
>>> +#include "xen_snd_front_cfg.h"
>>> +#include "xen_snd_front_evtchnl.h"
>>> +
>>> +static irqreturn_t evtchnl_interrupt_req(int irq, void *dev_id)
>>> +{
>>> +    struct xen_snd_front_evtchnl *channel = dev_id;
>>> +    struct xen_snd_front_info *front_info = channel->front_info;
>>> +    struct xensnd_resp *resp;
>>> +    RING_IDX i, rp;
>>> +    unsigned long flags;
>>> +
>>> +    if (unlikely(channel->state != EVTCHNL_STATE_CONNECTED))
>>> +        return IRQ_HANDLED;
>>> +
>>> +    spin_lock_irqsave(&front_info->io_lock, flags);
>>> +
>>> +again:
>>> +    rp = channel->u.req.ring.sring->rsp_prod;
>>> +    /* ensure we see queued responses up to rp */
>>> +    rmb();
>>> +
>>> +    for (i = channel->u.req.ring.rsp_cons; i != rp; i++) {
>>> +        resp = RING_GET_RESPONSE(&channel->u.req.ring, i);
>>> +        if (resp->id != channel->evt_id)
>>> +            continue;
>>> +        switch (resp->operation) {
>>> +        case XENSND_OP_OPEN:
>>> +            /* fall through */
>>> +        case XENSND_OP_CLOSE:
>>> +            /* fall through */
>>> +        case XENSND_OP_READ:
>>> +            /* fall through */
>>> +        case XENSND_OP_WRITE:
>>> +            /* fall through */
>>> +        case XENSND_OP_TRIGGER:
>>> +            channel->u.req.resp_status = resp->status;
>>> +            complete(&channel->u.req.completion);
>>> +            break;
>>> +        case XENSND_OP_HW_PARAM_QUERY:
>>> +            channel->u.req.resp_status = resp->status;
>>> +            channel->u.req.resp.hw_param =
>>> +                    resp->resp.hw_param;
>>> +            complete(&channel->u.req.completion);
>>> +            break;
>>> +
>>> +        default:
>>> +            dev_err(&front_info->xb_dev->dev,
>>> +                "Operation %d is not supported\n",
>>> +                resp->operation);
>>> +            break;
>>> +        }
>>> +    }
>>> +
>>> +    channel->u.req.ring.rsp_cons = i;
>>> +    if (i != channel->u.req.ring.req_prod_pvt) {
>>> +        int more_to_do;
>>> +
>>> +        RING_FINAL_CHECK_FOR_RESPONSES(&channel->u.req.ring,
>>> +                           more_to_do);
>>> +        if (more_to_do)
>>> +            goto again;
>>> +    } else {
>>> +        channel->u.req.ring.sring->rsp_event = i + 1;
>>> +    }
>>> +
>>> +    spin_unlock_irqrestore(&front_info->io_lock, flags);
>>> +    return IRQ_HANDLED;
>>> +}
>>> +
>>> +static irqreturn_t evtchnl_interrupt_evt(int irq, void *dev_id)
>>> +{
>>> +    struct xen_snd_front_evtchnl *channel = dev_id;
>>> +    struct xen_snd_front_info *front_info = channel->front_info;
>>> +    struct xensnd_event_page *page = channel->u.evt.page;
>>> +    u32 cons, prod;
>>> +    unsigned long flags;
>>> +
>>> +    if (unlikely(channel->state != EVTCHNL_STATE_CONNECTED))
>>> +        return IRQ_HANDLED;
>>> +
>>> +    spin_lock_irqsave(&front_info->io_lock, flags);
>>> +
>>> +    prod = page->in_prod;
>>> +    /* ensure we see ring contents up to prod */
>>> +    virt_rmb();
>>> +    if (prod == page->in_cons)
>>> +        goto out;
>>> +
>>> +    for (cons = page->in_cons; cons != prod; cons++) {
>>> +        struct xensnd_evt *event;
>>> +
>>> +        event = &XENSND_IN_RING_REF(page, cons);
>>> +        if (unlikely(event->id != channel->evt_id++))
>>> +            continue;
>>> +
>>> +        switch (event->type) {
>>> +        case XENSND_EVT_CUR_POS:
>>> +            /* do nothing at the moment */
>>> +            break;
>>> +        }
>>> +    }
>>> +
>>> +    page->in_cons = cons;
>>> +    /* ensure ring contents */
>>> +    virt_wmb();
>>> +
>>> +out:
>>> +    spin_unlock_irqrestore(&front_info->io_lock, flags);
>>> +    return IRQ_HANDLED;
>>> +}
>>> +
>>> +void xen_snd_front_evtchnl_flush(struct xen_snd_front_evtchnl *channel)
>>> +{
>>> +    int notify;
>>> +
>>> +    channel->u.req.ring.req_prod_pvt++;
>>> +    RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(&channel->u.req.ring, notify);
>>> +    if (notify)
>>> +        notify_remote_via_irq(channel->irq);
>>> +}
>>> +
>>> +static void evtchnl_free(struct xen_snd_front_info *front_info,
>>> +             struct xen_snd_front_evtchnl *channel)
>>> +{
>>> +    unsigned long page = 0;
>>> +
>>> +    if (channel->type == EVTCHNL_TYPE_REQ)
>>> +        page = (unsigned long)channel->u.req.ring.sring;
>>> +    else if (channel->type == EVTCHNL_TYPE_EVT)
>>> +        page = (unsigned long)channel->u.evt.page;
>>> +
>>> +    if (!page)
>>> +        return;
>>> +
>>> +    channel->state = EVTCHNL_STATE_DISCONNECTED;
>>> +    if (channel->type == EVTCHNL_TYPE_REQ) {
>>> +        /* release all who still waits for response if any */
>>> +        channel->u.req.resp_status = -EIO;
>>> +        complete_all(&channel->u.req.completion);
>>> +    }
>>> +
>>> +    if (channel->irq)
>>> +        unbind_from_irqhandler(channel->irq, channel);
>>> +
>>> +    if (channel->port)
>>> +        xenbus_free_evtchn(front_info->xb_dev, channel->port);
>>> +
>>> +    /* end access and free the page */
>>> +    if (channel->gref != GRANT_INVALID_REF)
>>> +        gnttab_end_foreign_access(channel->gref, 0, page);
>> Free page?
> According to [1] if page is provided to gnttab_end_foreign_access
> it will be freed. So, no need to free it manually

Either a free_page() is missing here in an else clause or the if is
not necessary.


Juergen