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Subject: Re: [PATCH v2 5/5] ALSA: xen-front: Implement ALSA virtual sound
 driver
From: Oleksandr Andrushchenko <andr2000@gmail.com>
To: Juergen Gross <jgross@suse.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>
 <20180416062453.24743-6-andr2000@gmail.com>
 <f8ec79c7-1b6f-dd00-5bd3-fc9fb8b42de1@suse.com>
 <e77fe463-68aa-b117-84c5-6dc729a3df42@gmail.com>
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Date: Tue, 17 Apr 2018 15:26:16 +0300
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On 04/17/2018 02:32 PM, Oleksandr Andrushchenko wrote:
> On 04/16/2018 05:09 PM, Juergen Gross wrote:
>> On 16/04/18 08:24, Oleksandr Andrushchenko wrote:
>>> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
>>>
>>> Implement essential initialization of the sound driver:
>>>    - introduce required data structures
>>>    - handle driver registration
>>>    - handle sound card registration
>>>    - register sound driver on backend connection
>>>    - remove sound driver on backend disconnect
>>>
>>> Initialize virtual sound card with streams according to the
>>> Xen store configuration.
>>>
>>> Implement ALSA driver operations including:
>>> - manage frontend/backend shared buffers
>>> - manage Xen bus event channel states
>>>
>>> Implement requests from front to back for ALSA
>>> PCM operations.
>>>   - report ALSA period elapsed event: handle XENSND_EVT_CUR_POS
>>>     notifications from the backend when stream position advances
>>>     during playback/capture. The event carries a value of how
>>>     many octets were played/captured at the time of the event.
>>>   - implement explicit stream parameter negotiation between
>>>     backend and frontend: handle XENSND_OP_HW_PARAM_QUERY request
>>>     to read/update configuration space for the parameter given:
>>>     request passes desired parameter interval and the response to
>>>     this request returns min/max interval for the parameter to be used.
>>>
>>> Signed-off-by: Oleksandr Andrushchenko 
>>> <oleksandr_andrushchenko@epam.com>
>>> ---
>>>   sound/xen/Makefile                |   3 +-
>>>   sound/xen/xen_snd_front.c         | 193 ++++++++-
>>>   sound/xen/xen_snd_front.h         |  28 ++
>>>   sound/xen/xen_snd_front_alsa.c    | 830 
>>> ++++++++++++++++++++++++++++++++++++++
>>>   sound/xen/xen_snd_front_alsa.h    |  23 ++
>>>   sound/xen/xen_snd_front_evtchnl.c |   6 +-
>>>   6 files changed, 1080 insertions(+), 3 deletions(-)
>>>   create mode 100644 sound/xen/xen_snd_front_alsa.c
>>>   create mode 100644 sound/xen/xen_snd_front_alsa.h
>>>
>>> diff --git a/sound/xen/Makefile b/sound/xen/Makefile
>>> index f028bc30af5d..1e6470ecc2f2 100644
>>> --- a/sound/xen/Makefile
>>> +++ b/sound/xen/Makefile
>>> @@ -3,6 +3,7 @@
>>>   snd_xen_front-objs := xen_snd_front.o \
>>>                 xen_snd_front_cfg.o \
>>>                 xen_snd_front_evtchnl.o \
>>> -              xen_snd_front_shbuf.o
>>> +              xen_snd_front_shbuf.o \
>>> +              xen_snd_front_alsa.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 0569c6c596a3..1fef253ea21a 100644
>>> --- a/sound/xen/xen_snd_front.c
>>> +++ b/sound/xen/xen_snd_front.c
>>> @@ -19,10 +19,201 @@
>>>   #include <xen/interface/io/sndif.h>
>>>     #include "xen_snd_front.h"
>>> +#include "xen_snd_front_alsa.h"
>>>   #include "xen_snd_front_evtchnl.h"
>>> +#include "xen_snd_front_shbuf.h"
>>> +
>>> +static struct xensnd_req *
>>> +be_stream_prepare_req(struct xen_snd_front_evtchnl *evtchnl, u8 
>>> operation)
>>> +{
>>> +    struct xensnd_req *req;
>>> +
>>> +    req = RING_GET_REQUEST(&evtchnl->u.req.ring,
>>> +                   evtchnl->u.req.ring.req_prod_pvt);
>>> +    req->operation = operation;
>>> +    req->id = evtchnl->evt_next_id++;
>>> +    evtchnl->evt_id = req->id;
>>> +    return req;
>>> +}
>>> +
>>> +static int be_stream_do_io(struct xen_snd_front_evtchnl *evtchnl)
>>> +{
>>> +    if (unlikely(evtchnl->state != EVTCHNL_STATE_CONNECTED))
>>> +        return -EIO;
>>> +
>>> +    reinit_completion(&evtchnl->u.req.completion);
>>> +    xen_snd_front_evtchnl_flush(evtchnl);
>>> +    return 0;
>>> +}
>>> +
>>> +static int be_stream_wait_io(struct xen_snd_front_evtchnl *evtchnl)
>>> +{
>>> +    if (wait_for_completion_timeout(&evtchnl->u.req.completion,
>>> +            msecs_to_jiffies(VSND_WAIT_BACK_MS)) <= 0)
>>> +        return -ETIMEDOUT;
>>> +
>>> +    return evtchnl->u.req.resp_status;
>>> +}
>>> +
>>> +int xen_snd_front_stream_query_hw_param(struct 
>>> xen_snd_front_evtchnl *evtchnl,
>>> +                    struct xensnd_query_hw_param *hw_param_req,
>>> +                    struct xensnd_query_hw_param *hw_param_resp)
>>> +{
>>> +    struct xen_snd_front_info *front_info = evtchnl->front_info;
>>> +    struct xensnd_req *req;
>>> +    unsigned long flags;
>>> +    int ret;
>>> +
>>> +    mutex_lock(&evtchnl->u.req.req_io_lock);
>>> +
>>> +    spin_lock_irqsave(&front_info->io_lock, flags);
>>> +    req = be_stream_prepare_req(evtchnl, XENSND_OP_HW_PARAM_QUERY);
>>> +    req->op.hw_param = *hw_param_req;
>>> +
>>> +    ret = be_stream_do_io(evtchnl);
>>> +    spin_unlock_irqrestore(&front_info->io_lock, flags);
>>> +
>>> +    if (ret == 0)
>>> +        ret = be_stream_wait_io(evtchnl);
>>> +
>>> +    if (ret == 0)
>>> +        *hw_param_resp = evtchnl->u.req.resp.hw_param;
>>> +
>>> +    mutex_unlock(&evtchnl->u.req.req_io_lock);
>>> +    return ret;
>>> +}
>>> +
>>> +int xen_snd_front_stream_prepare(struct xen_snd_front_evtchnl 
>>> *evtchnl,
>>> +                 struct xen_snd_front_shbuf *sh_buf,
>>> +                 u8 format, unsigned int channels,
>>> +                 unsigned int rate, u32 buffer_sz,
>>> +                 u32 period_sz)
>>> +{
>>> +    struct xen_snd_front_info *front_info = evtchnl->front_info;
>>> +    struct xensnd_req *req;
>>> +    unsigned long flags;
>>> +    int ret;
>>> +
>>> +    mutex_lock(&evtchnl->u.req.req_io_lock);
>>> +
>>> +    spin_lock_irqsave(&front_info->io_lock, flags);
>>> +    req = be_stream_prepare_req(evtchnl, XENSND_OP_OPEN);
>>> +    req->op.open.pcm_format = format;
>>> +    req->op.open.pcm_channels = channels;
>>> +    req->op.open.pcm_rate = rate;
>>> +    req->op.open.buffer_sz = buffer_sz;
>>> +    req->op.open.period_sz = period_sz;
>>> +    req->op.open.gref_directory = 
>>> xen_snd_front_shbuf_get_dir_start(sh_buf);
>>> +
>>> +    ret = be_stream_do_io(evtchnl);
>>> +    spin_unlock_irqrestore(&front_info->io_lock, flags);
>>> +
>>> +    if (ret == 0)
>>> +        ret = be_stream_wait_io(evtchnl);
>>> +
>>> +    mutex_unlock(&evtchnl->u.req.req_io_lock);
>>> +    return ret;
>>> +}
>>> +
>>> +int xen_snd_front_stream_close(struct xen_snd_front_evtchnl *evtchnl)
>>> +{
>>> +    struct xen_snd_front_info *front_info = evtchnl->front_info;
>>> +    struct xensnd_req *req;
>>> +    unsigned long flags;
>>> +    int ret;
>>> +
>>> +    mutex_lock(&evtchnl->u.req.req_io_lock);
>>> +
>>> +    spin_lock_irqsave(&front_info->io_lock, flags);
>>> +    req = be_stream_prepare_req(evtchnl, XENSND_OP_CLOSE);
>>> +
>>> +    ret = be_stream_do_io(evtchnl);
>>> +    spin_unlock_irqrestore(&front_info->io_lock, flags);
>>> +
>>> +    if (ret == 0)
>>> +        ret = be_stream_wait_io(evtchnl);
>>> +
>>> +    mutex_unlock(&evtchnl->u.req.req_io_lock);
>>> +    return ret;
>>> +}
>>> +
>>> +int xen_snd_front_stream_write(struct xen_snd_front_evtchnl *evtchnl,
>>> +                   unsigned long pos, unsigned long count)
>>> +{
>>> +    struct xen_snd_front_info *front_info = evtchnl->front_info;
>>> +    struct xensnd_req *req;
>>> +    unsigned long flags;
>>> +    int ret;
>>> +
>>> +    mutex_lock(&evtchnl->u.req.req_io_lock);
>>> +
>>> +    spin_lock_irqsave(&front_info->io_lock, flags);
>>> +    req = be_stream_prepare_req(evtchnl, XENSND_OP_WRITE);
>>> +    req->op.rw.length = count;
>>> +    req->op.rw.offset = pos;
>>> +
>>> +    ret = be_stream_do_io(evtchnl);
>>> +    spin_unlock_irqrestore(&front_info->io_lock, flags);
>>> +
>>> +    if (ret == 0)
>>> +        ret = be_stream_wait_io(evtchnl);
>>> +
>>> +    mutex_unlock(&evtchnl->u.req.req_io_lock);
>>> +    return ret;
>>> +}
>>> +
>>> +int xen_snd_front_stream_read(struct xen_snd_front_evtchnl *evtchnl,
>>> +                  unsigned long pos, unsigned long count)
>>> +{
>>> +    struct xen_snd_front_info *front_info = evtchnl->front_info;
>>> +    struct xensnd_req *req;
>>> +    unsigned long flags;
>>> +    int ret;
>>> +
>>> +    mutex_lock(&evtchnl->u.req.req_io_lock);
>>> +
>>> +    spin_lock_irqsave(&front_info->io_lock, flags);
>>> +    req = be_stream_prepare_req(evtchnl, XENSND_OP_READ);
>>> +    req->op.rw.length = count;
>>> +    req->op.rw.offset = pos;
>>> +
>>> +    ret = be_stream_do_io(evtchnl);
>>> +    spin_unlock_irqrestore(&front_info->io_lock, flags);
>>> +
>>> +    if (ret == 0)
>>> +        ret = be_stream_wait_io(evtchnl);
>>> +
>>> +    mutex_unlock(&evtchnl->u.req.req_io_lock);
>>> +    return ret;
>>> +}
>>> +
>>> +int xen_snd_front_stream_trigger(struct xen_snd_front_evtchnl 
>>> *evtchnl,
>>> +                 int type)
>>> +{
>>> +    struct xen_snd_front_info *front_info = evtchnl->front_info;
>>> +    struct xensnd_req *req;
>>> +    unsigned long flags;
>>> +    int ret;
>>> +
>>> +    mutex_lock(&evtchnl->u.req.req_io_lock);
>>> +
>>> +    spin_lock_irqsave(&front_info->io_lock, flags);
>>> +    req = be_stream_prepare_req(evtchnl, XENSND_OP_TRIGGER);
>>> +    req->op.trigger.type = type;
>>> +
>>> +    ret = be_stream_do_io(evtchnl);
>>> +    spin_unlock_irqrestore(&front_info->io_lock, flags);
>>> +
>>> +    if (ret == 0)
>>> +        ret = be_stream_wait_io(evtchnl);
>>> +
>>> +    mutex_unlock(&evtchnl->u.req.req_io_lock);
>>> +    return ret;
>>> +}
>>>     static void xen_snd_drv_fini(struct xen_snd_front_info *front_info)
>>>   {
>>> +    xen_snd_front_alsa_fini(front_info);
>>>       xen_snd_front_evtchnl_free_all(front_info);
>>>   }
>>>   @@ -45,7 +236,7 @@ static int sndback_initwait(struct 
>>> xen_snd_front_info *front_info)
>>>     static int sndback_connect(struct xen_snd_front_info *front_info)
>>>   {
>>> -    return 0;
>>> +    return xen_snd_front_alsa_init(front_info);
>>>   }
>>>     static void sndback_disconnect(struct xen_snd_front_info 
>>> *front_info)
>>> diff --git a/sound/xen/xen_snd_front.h b/sound/xen/xen_snd_front.h
>>> index 9c2ffbb4e4b8..7adbdb4d2019 100644
>>> --- a/sound/xen/xen_snd_front.h
>>> +++ b/sound/xen/xen_snd_front.h
>>> @@ -13,17 +13,45 @@
>>>     #include "xen_snd_front_cfg.h"
>>>   +struct card_info;
>>> +struct xen_snd_front_evtchnl;
>>>   struct xen_snd_front_evtchnl_pair;
>>> +struct xen_snd_front_shbuf;
>>> +struct xensnd_query_hw_param;
>>>     struct xen_snd_front_info {
>>>       struct xenbus_device *xb_dev;
>>>   +    struct card_info *card_info;
>>> +
>>>       /* 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;
>>>   };
>>>   +int xen_snd_front_stream_query_hw_param(struct 
>>> xen_snd_front_evtchnl *evtchnl,
>>> +                    struct xensnd_query_hw_param *hw_param_req,
>>> +                    struct xensnd_query_hw_param *hw_param_resp);
>>> +
>>> +int xen_snd_front_stream_prepare(struct xen_snd_front_evtchnl 
>>> *evtchnl,
>>> +                 struct xen_snd_front_shbuf *sh_buf,
>>> +                 u8 format, unsigned int channels,
>>> +                 unsigned int rate, u32 buffer_sz,
>>> +                 u32 period_sz);
>>> +
>>> +int xen_snd_front_stream_close(struct xen_snd_front_evtchnl *evtchnl);
>>> +
>>> +int xen_snd_front_stream_write(struct xen_snd_front_evtchnl *evtchnl,
>>> +                   unsigned long pos, unsigned long count);
>>> +
>>> +int xen_snd_front_stream_read(struct xen_snd_front_evtchnl *evtchnl,
>>> +                  unsigned long pos, unsigned long count);
>>> +
>>> +int xen_snd_front_stream_trigger(struct xen_snd_front_evtchnl 
>>> *evtchnl,
>>> +                 int type);
>>> +
>>>   #endif /* __XEN_SND_FRONT_H */
>>> diff --git a/sound/xen/xen_snd_front_alsa.c 
>>> b/sound/xen/xen_snd_front_alsa.c
>>> new file mode 100644
>>> index 000000000000..f524b172750e
>>> --- /dev/null
>>> +++ b/sound/xen/xen_snd_front_alsa.c
>>> @@ -0,0 +1,830 @@
>>> +// 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 <linux/platform_device.h>
>>> +
>>> +#include <sound/core.h>
>>> +#include <sound/pcm.h>
>>> +#include <sound/pcm_params.h>
>>> +
>>> +#include <xen/xenbus.h>
>>> +
>>> +#include "xen_snd_front.h"
>>> +#include "xen_snd_front_alsa.h"
>>> +#include "xen_snd_front_cfg.h"
>>> +#include "xen_snd_front_evtchnl.h"
>>> +#include "xen_snd_front_shbuf.h"
>>> +
>>> +struct pcm_stream_info {
>> Not sure how this is generally handled in the sound drivers, but when
>> reviewing the code using those structures I repeatedly tried to find
>> their definitions in the sound headers instead of here. Same applies to
>> the alsa_* names.
>>
>> I'd prefer names which don't poison the name space.
> I'll try to do something about naming
One question still remains wrt alsa_* names: if this is for structures
I have (alsa_sndif_sample_format/alsa_sndif_hw_param), then
those already have sndif in their name which clearly says these are
Xen related ones (sndif is a Xen protocol).
If you also don't like the alsa_* function names then those are all
static and defined in this same file, so see no confusion here.

I have changed other non-obvious struct names:

-struct pcm_stream_info {
+struct xen_snd_front_pcm_stream_info {

-struct pcm_instance_info {
+struct xen_snd_front_pcm_instance_info {

-struct card_info {
+struct xen_snd_front_card_info {

Does the above work for you?
>>> +    struct xen_snd_front_info *front_info;
>>> +    struct xen_snd_front_evtchnl_pair *evt_pair;
>>> +    struct xen_snd_front_shbuf sh_buf;
>>> +    int index;
>>> +
>>> +    bool is_open;
>>> +    struct snd_pcm_hardware pcm_hw;
>>> +
>>> +    /* number of processed frames as reported by the backend */
>>> +    snd_pcm_uframes_t be_cur_frame;
>>> +    /* current HW pointer to be reported via .period callback */
>>> +    atomic_t hw_ptr;
>>> +    /* modulo of the number of processed frames - for period 
>>> detection */
>>> +    u32 out_frames;
>>> +};
>>> +
>>> +struct pcm_instance_info {
>>> +    struct card_info *card_info;
>>> +    struct snd_pcm *pcm;
>>> +    struct snd_pcm_hardware pcm_hw;
>>> +    int num_pcm_streams_pb;
>>> +    struct pcm_stream_info *streams_pb;
>>> +    int num_pcm_streams_cap;
>>> +    struct pcm_stream_info *streams_cap;
>>> +};
>>> +
>>> +struct card_info {
>>> +    struct xen_snd_front_info *front_info;
>>> +    struct snd_card *card;
>>> +    struct snd_pcm_hardware pcm_hw;
>>> +    int num_pcm_instances;
>>> +    struct pcm_instance_info *pcm_instances;
>>> +};
>>> +
>>> +struct alsa_sndif_sample_format {
>>> +    u8 sndif;
>>> +    snd_pcm_format_t alsa;
>>> +};
>>> +
>>> +struct alsa_sndif_hw_param {
>>> +    u8 sndif;
>>> +    snd_pcm_hw_param_t alsa;
>>> +};
>>> +
>>> +static const struct alsa_sndif_sample_format ALSA_SNDIF_FORMATS[] = {
>>> +    {
>>> +        .sndif = XENSND_PCM_FORMAT_U8,
>>> +        .alsa = SNDRV_PCM_FORMAT_U8
>>> +    },
>>> +    {
>>> +        .sndif = XENSND_PCM_FORMAT_S8,
>>> +        .alsa = SNDRV_PCM_FORMAT_S8
>>> +    },
>>> +    {
>>> +        .sndif = XENSND_PCM_FORMAT_U16_LE,
>>> +        .alsa = SNDRV_PCM_FORMAT_U16_LE
>>> +    },
>>> +    {
>>> +        .sndif = XENSND_PCM_FORMAT_U16_BE,
>>> +        .alsa = SNDRV_PCM_FORMAT_U16_BE
>>> +    },
>>> +    {
>>> +        .sndif = XENSND_PCM_FORMAT_S16_LE,
>>> +        .alsa = SNDRV_PCM_FORMAT_S16_LE
>>> +    },
>>> +    {
>>> +        .sndif = XENSND_PCM_FORMAT_S16_BE,
>>> +        .alsa = SNDRV_PCM_FORMAT_S16_BE
>>> +    },
>>> +    {
>>> +        .sndif = XENSND_PCM_FORMAT_U24_LE,
>>> +        .alsa = SNDRV_PCM_FORMAT_U24_LE
>>> +    },
>>> +    {
>>> +        .sndif = XENSND_PCM_FORMAT_U24_BE,
>>> +        .alsa = SNDRV_PCM_FORMAT_U24_BE
>>> +    },
>>> +    {
>>> +        .sndif = XENSND_PCM_FORMAT_S24_LE,
>>> +        .alsa = SNDRV_PCM_FORMAT_S24_LE
>>> +    },
>>> +    {
>>> +        .sndif = XENSND_PCM_FORMAT_S24_BE,
>>> +        .alsa = SNDRV_PCM_FORMAT_S24_BE
>>> +    },
>>> +    {
>>> +        .sndif = XENSND_PCM_FORMAT_U32_LE,
>>> +        .alsa = SNDRV_PCM_FORMAT_U32_LE
>>> +    },
>>> +    {
>>> +        .sndif = XENSND_PCM_FORMAT_U32_BE,
>>> +        .alsa = SNDRV_PCM_FORMAT_U32_BE
>>> +    },
>>> +    {
>>> +        .sndif = XENSND_PCM_FORMAT_S32_LE,
>>> +        .alsa = SNDRV_PCM_FORMAT_S32_LE
>>> +    },
>>> +    {
>>> +        .sndif = XENSND_PCM_FORMAT_S32_BE,
>>> +        .alsa = SNDRV_PCM_FORMAT_S32_BE
>>> +    },
>>> +    {
>>> +        .sndif = XENSND_PCM_FORMAT_A_LAW,
>>> +        .alsa = SNDRV_PCM_FORMAT_A_LAW
>>> +    },
>>> +    {
>>> +        .sndif = XENSND_PCM_FORMAT_MU_LAW,
>>> +        .alsa = SNDRV_PCM_FORMAT_MU_LAW
>>> +    },
>>> +    {
>>> +        .sndif = XENSND_PCM_FORMAT_F32_LE,
>>> +        .alsa = SNDRV_PCM_FORMAT_FLOAT_LE
>>> +    },
>>> +    {
>>> +        .sndif = XENSND_PCM_FORMAT_F32_BE,
>>> +        .alsa = SNDRV_PCM_FORMAT_FLOAT_BE
>>> +    },
>>> +    {
>>> +        .sndif = XENSND_PCM_FORMAT_F64_LE,
>>> +        .alsa = SNDRV_PCM_FORMAT_FLOAT64_LE
>>> +    },
>>> +    {
>>> +        .sndif = XENSND_PCM_FORMAT_F64_BE,
>>> +        .alsa = SNDRV_PCM_FORMAT_FLOAT64_BE
>>> +    },
>>> +    {
>>> +        .sndif = XENSND_PCM_FORMAT_IEC958_SUBFRAME_LE,
>>> +        .alsa = SNDRV_PCM_FORMAT_IEC958_SUBFRAME_LE
>>> +    },
>>> +    {
>>> +        .sndif = XENSND_PCM_FORMAT_IEC958_SUBFRAME_BE,
>>> +        .alsa = SNDRV_PCM_FORMAT_IEC958_SUBFRAME_BE
>>> +    },
>>> +    {
>>> +        .sndif = XENSND_PCM_FORMAT_IMA_ADPCM,
>>> +        .alsa = SNDRV_PCM_FORMAT_IMA_ADPCM
>>> +    },
>>> +    {
>>> +        .sndif = XENSND_PCM_FORMAT_MPEG,
>>> +        .alsa = SNDRV_PCM_FORMAT_MPEG
>>> +    },
>>> +    {
>>> +        .sndif = XENSND_PCM_FORMAT_GSM,
>>> +        .alsa = SNDRV_PCM_FORMAT_GSM
>>> +    },
>>> +};
>>> +
>>> +static int to_sndif_format(snd_pcm_format_t format)
>>> +{
>>> +    int i;
>>> +
>>> +    for (i = 0; i < ARRAY_SIZE(ALSA_SNDIF_FORMATS); i++)
>>> +        if (ALSA_SNDIF_FORMATS[i].alsa == format)
>>> +            return ALSA_SNDIF_FORMATS[i].sndif;
>>> +
>>> +    return -EINVAL;
>>> +}
>>> +
>>> +static u64 to_sndif_formats_mask(u64 alsa_formats)
>>> +{
>>> +    u64 mask;
>>> +    int i;
>>> +
>>> +    mask = 0;
>>> +    for (i = 0; i < ARRAY_SIZE(ALSA_SNDIF_FORMATS); i++)
>>> +        if (1 << ALSA_SNDIF_FORMATS[i].alsa & alsa_formats)
>>> +            mask |= 1 << ALSA_SNDIF_FORMATS[i].sndif;
>>> +
>>> +    return mask;
>>> +}
>>> +
>>> +static u64 to_alsa_formats_mask(u64 sndif_formats)
>>> +{
>>> +    u64 mask;
>>> +    int i;
>>> +
>>> +    mask = 0;
>>> +    for (i = 0; i < ARRAY_SIZE(ALSA_SNDIF_FORMATS); i++)
>>> +        if (1 << ALSA_SNDIF_FORMATS[i].sndif & sndif_formats)
>>> +            mask |= 1 << ALSA_SNDIF_FORMATS[i].alsa;
>>> +
>>> +    return mask;
>>> +}
>>> +
>>> +static void stream_clear(struct pcm_stream_info *stream)
>>> +{
>>> +    stream->is_open = false;
>>> +    stream->be_cur_frame = 0;
>>> +    stream->out_frames = 0;
>>> +    atomic_set(&stream->hw_ptr, 0);
>>> +    xen_snd_front_evtchnl_pair_clear(stream->evt_pair);
>>> +    xen_snd_front_shbuf_clear(&stream->sh_buf);
>>> +}
>>> +
>>> +static void stream_free(struct pcm_stream_info *stream)
>>> +{
>>> +    xen_snd_front_shbuf_free(&stream->sh_buf);
>>> +    stream_clear(stream);
>>> +}
>>> +
>>> +static struct pcm_stream_info *stream_get(struct snd_pcm_substream 
>>> *substream)
>>> +{
>>> +    struct pcm_instance_info *pcm_instance =
>>> +            snd_pcm_substream_chip(substream);
>>> +    struct pcm_stream_info *stream;
>>> +
>>> +    if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK)
>>> +        stream = &pcm_instance->streams_pb[substream->number];
>>> +    else
>>> +        stream = &pcm_instance->streams_cap[substream->number];
>>> +
>>> +    return stream;
>>> +}
>>> +
>>> +static int alsa_hw_rule(struct snd_pcm_hw_params *params,
>>> +            struct snd_pcm_hw_rule *rule)
>>> +{
>>> +    struct pcm_stream_info *stream = rule->private;
>>> +    struct device *dev = &stream->front_info->xb_dev->dev;
>>> +    struct snd_mask *formats =
>>> +            hw_param_mask(params, SNDRV_PCM_HW_PARAM_FORMAT);
>>> +    struct snd_interval *rates =
>>> +            hw_param_interval(params, SNDRV_PCM_HW_PARAM_RATE);
>>> +    struct snd_interval *channels =
>>> +            hw_param_interval(params, SNDRV_PCM_HW_PARAM_CHANNELS);
>>> +    struct snd_interval *period =
>>> +            hw_param_interval(params,
>>> +                      SNDRV_PCM_HW_PARAM_PERIOD_SIZE);
>>> +    struct snd_interval *buffer =
>>> +            hw_param_interval(params,
>>> +                      SNDRV_PCM_HW_PARAM_BUFFER_SIZE);
>>> +    struct xensnd_query_hw_param req;
>>> +    struct xensnd_query_hw_param resp;
>>> +    struct snd_interval interval;
>>> +    struct snd_mask mask;
>>> +    u64 sndif_formats;
>>> +    int changed, ret;
>>> +
>>> +    /* collect all the values we need for the query */
>>> +
>>> +    req.formats = to_sndif_formats_mask((u64)formats->bits[0] |
>>> +                        (u64)(formats->bits[1]) << 32);
>>> +
>>> +    req.rates.min = rates->min;
>>> +    req.rates.max = rates->max;
>>> +
>>> +    req.channels.min = channels->min;
>>> +    req.channels.max = channels->max;
>>> +
>>> +    req.buffer.min = buffer->min;
>>> +    req.buffer.max = buffer->max;
>>> +
>>> +    req.period.min = period->min;
>>> +    req.period.max = period->max;
>>> +
>>> +    ret = xen_snd_front_stream_query_hw_param(&stream->evt_pair->req,
>>> +                          &req, &resp);
>>> +    if (ret < 0) {
>>> +        /* check if this is due to backend communication error */
>>> +        if (ret == -EIO || ret == -ETIMEDOUT)
>>> +            dev_err(dev, "Failed to query ALSA HW parameters\n");
>>> +        return ret;
>>> +    }
>>> +
>>> +    /* refine HW parameters after the query */
>>> +    changed  = 0;
>>> +
>>> +    sndif_formats = to_alsa_formats_mask(resp.formats);
>>> +    snd_mask_none(&mask);
>>> +    mask.bits[0] = (u32)sndif_formats;
>>> +    mask.bits[1] = (u32)(sndif_formats >> 32);
>>> +    ret = snd_mask_refine(formats, &mask);
>>> +    if (ret < 0)
>>> +        return ret;
>>> +    changed |= ret;
>>> +
>>> +    interval.openmin = 0;
>>> +    interval.openmax = 0;
>>> +    interval.integer = 1;
>>> +
>>> +    interval.min = resp.rates.min;
>>> +    interval.max = resp.rates.max;
>>> +    ret = snd_interval_refine(rates, &interval);
>>> +    if (ret < 0)
>>> +        return ret;
>>> +    changed |= ret;
>>> +
>>> +    interval.min = resp.channels.min;
>>> +    interval.max = resp.channels.max;
>>> +    ret = snd_interval_refine(channels, &interval);
>>> +    if (ret < 0)
>>> +        return ret;
>>> +    changed |= ret;
>>> +
>>> +    interval.min = resp.buffer.min;
>>> +    interval.max = resp.buffer.max;
>>> +    ret = snd_interval_refine(buffer, &interval);
>>> +    if (ret < 0)
>>> +        return ret;
>>> +    changed |= ret;
>>> +
>>> +    interval.min = resp.period.min;
>>> +    interval.max = resp.period.max;
>>> +    ret = snd_interval_refine(period, &interval);
>>> +    if (ret < 0)
>>> +        return ret;
>>> +    changed |= ret;
>>> +
>>> +    return changed;
>>> +}
>>> +
>>> +static int alsa_open(struct snd_pcm_substream *substream)
>>> +{
>>> +    struct pcm_instance_info *pcm_instance =
>>> +            snd_pcm_substream_chip(substream);
>>> +    struct pcm_stream_info *stream = stream_get(substream);
>>> +    struct snd_pcm_runtime *runtime = substream->runtime;
>>> +    struct xen_snd_front_info *front_info =
>>> +            pcm_instance->card_info->front_info;
>>> +    struct device *dev = &front_info->xb_dev->dev;
>>> +    unsigned long flags;
>>> +    int ret;
>>> +
>>> +    /*
>>> +     * return our HW properties: override defaults with those 
>>> configured
>>> +     * via XenStore
>>> +     */
>>> +    runtime->hw = stream->pcm_hw;
>>> +    runtime->hw.info &= ~(SNDRV_PCM_INFO_MMAP |
>>> +                  SNDRV_PCM_INFO_MMAP_VALID |
>>> +                  SNDRV_PCM_INFO_DOUBLE |
>>> +                  SNDRV_PCM_INFO_BATCH |
>>> +                  SNDRV_PCM_INFO_NONINTERLEAVED |
>>> +                  SNDRV_PCM_INFO_RESUME |
>>> +                  SNDRV_PCM_INFO_PAUSE);
>>> +    runtime->hw.info |= SNDRV_PCM_INFO_INTERLEAVED;
>>> +
>>> +    spin_lock_irqsave(&front_info->io_lock, flags);
>>> +
>>> +    stream->evt_pair = &front_info->evt_pairs[stream->index];
>>> +
>>> +    stream->front_info = front_info;
>>> +
>>> + xen_snd_front_evtchnl_pair_set_connected(stream->evt_pair, true);
>>> +
>>> +    stream->evt_pair->evt.u.evt.substream = substream;
>>> +
>>> +    stream_clear(stream);
>>> +
>>> +    spin_unlock_irqrestore(&front_info->io_lock, flags);
>>> +
>>> +    ret = snd_pcm_hw_rule_add(runtime, 0, SNDRV_PCM_HW_PARAM_FORMAT,
>>> +                  alsa_hw_rule, stream,
>>> +                  SNDRV_PCM_HW_PARAM_FORMAT, -1);
>>> +    if (ret) {
>>> +        dev_err(dev, "Failed to add HW rule for 
>>> SNDRV_PCM_HW_PARAM_FORMAT\n");
>>> +        return ret;
>>> +    }
>>> +
>>> +    ret = snd_pcm_hw_rule_add(runtime, 0, SNDRV_PCM_HW_PARAM_RATE,
>>> +                  alsa_hw_rule, stream,
>>> +                  SNDRV_PCM_HW_PARAM_RATE, -1);
>>> +    if (ret) {
>>> +        dev_err(dev, "Failed to add HW rule for 
>>> SNDRV_PCM_HW_PARAM_RATE\n");
>>> +        return ret;
>>> +    }
>>> +
>>> +    ret = snd_pcm_hw_rule_add(runtime, 0, SNDRV_PCM_HW_PARAM_CHANNELS,
>>> +                  alsa_hw_rule, stream,
>>> +                  SNDRV_PCM_HW_PARAM_CHANNELS, -1);
>>> +    if (ret) {
>>> +        dev_err(dev, "Failed to add HW rule for 
>>> SNDRV_PCM_HW_PARAM_CHANNELS\n");
>>> +        return ret;
>>> +    }
>>> +
>>> +    ret = snd_pcm_hw_rule_add(runtime, 0, 
>>> SNDRV_PCM_HW_PARAM_PERIOD_SIZE,
>>> +                  alsa_hw_rule, stream,
>>> +                  SNDRV_PCM_HW_PARAM_PERIOD_SIZE, -1);
>>> +    if (ret) {
>>> +        dev_err(dev, "Failed to add HW rule for 
>>> SNDRV_PCM_HW_PARAM_PERIOD_SIZE\n");
>>> +        return ret;
>>> +    }
>>> +
>>> +    ret = snd_pcm_hw_rule_add(runtime, 0, 
>>> SNDRV_PCM_HW_PARAM_BUFFER_SIZE,
>>> +                  alsa_hw_rule, stream,
>>> +                  SNDRV_PCM_HW_PARAM_BUFFER_SIZE, -1);
>>> +    if (ret) {
>>> +        dev_err(dev, "Failed to add HW rule for 
>>> SNDRV_PCM_HW_PARAM_BUFFER_SIZE\n");
>>> +        return ret;
>>> +    }
>>> +
>>> +    return 0;
>>> +}
>>> +
>>> +static int alsa_close(struct snd_pcm_substream *substream)
>>> +{
>>> +    struct pcm_stream_info *stream = stream_get(substream);
>>> +    unsigned long flags;
>>> +
>>> +    spin_lock_irqsave(&stream->front_info->io_lock, flags);
>>> +
>>> + xen_snd_front_evtchnl_pair_set_connected(stream->evt_pair, false);
>>> +
>>> + spin_unlock_irqrestore(&stream->front_info->io_lock, flags);
>>> +    return 0;
>>> +}
>>> +
>>> +static int alsa_hw_params(struct snd_pcm_substream *substream,
>>> +              struct snd_pcm_hw_params *params)
>>> +{
>>> +    struct pcm_stream_info *stream = stream_get(substream);
>>> +    int ret;
>>> +
>>> +    /*
>>> +     * this callback may be called multiple times,
>>> +     * so free the previously allocated shared buffer if any
>>> +     */
>>> +    stream_free(stream);
>>> +
>>> +    ret = xen_snd_front_shbuf_alloc(stream->front_info->xb_dev,
>>> +                    &stream->sh_buf,
>>> +                    params_buffer_bytes(params));
>>> +    if (ret < 0) {
>>> +        stream_free(stream);
>>> + dev_err(&stream->front_info->xb_dev->dev,
>>> +            "Failed to allocate buffers for stream with index %d\n",
>>> +            stream->index);
>>> +        return ret;
>>> +    }
>>> +
>>> +    return 0;
>>> +}
>>> +
>>> +static int alsa_hw_free(struct snd_pcm_substream *substream)
>>> +{
>>> +    struct pcm_stream_info *stream = stream_get(substream);
>>> +    int ret;
>>> +
>>> +    ret = xen_snd_front_stream_close(&stream->evt_pair->req);
>>> +    stream_free(stream);
>>> +    return ret;
>>> +}
>>> +
>>> +static int alsa_prepare(struct snd_pcm_substream *substream)
>>> +{
>>> +    struct pcm_stream_info *stream = stream_get(substream);
>>> +
>>> +    if (!stream->is_open) {
>>> +        struct snd_pcm_runtime *runtime = substream->runtime;
>>> +        u8 sndif_format;
>>> +        int ret;
>>> +
>>> +        sndif_format = to_sndif_format(runtime->format);
>>> +        if (sndif_format < 0) {
>>> + dev_err(&stream->front_info->xb_dev->dev,
>>> +                "Unsupported sample format: %d\n",
>>> +                runtime->format);
>>> +            return sndif_format;
>>> +        }
>>> +
>>> +        ret = xen_snd_front_stream_prepare(&stream->evt_pair->req,
>>> +                           &stream->sh_buf,
>>> +                           sndif_format,
>>> +                           runtime->channels,
>>> +                           runtime->rate,
>>> + snd_pcm_lib_buffer_bytes(substream),
>>> + snd_pcm_lib_period_bytes(substream));
>>> +        if (ret < 0)
>>> +            return ret;
>>> +
>>> +        stream->is_open = true;
>>> +    }
>>> +
>>> +    return 0;
>>> +}
>>> +
>>> +static int alsa_trigger(struct snd_pcm_substream *substream, int cmd)
>>> +{
>>> +    struct pcm_stream_info *stream = stream_get(substream);
>>> +    int type;
>>> +
>>> +    switch (cmd) {
>>> +    case SNDRV_PCM_TRIGGER_START:
>>> +        type = XENSND_OP_TRIGGER_START;
>>> +        break;
>>> +
>>> +    case SNDRV_PCM_TRIGGER_RESUME:
>>> +        type = XENSND_OP_TRIGGER_RESUME;
>>> +        break;
>>> +
>>> +    case SNDRV_PCM_TRIGGER_STOP:
>>> +        type = XENSND_OP_TRIGGER_STOP;
>>> +        break;
>>> +
>>> +    case SNDRV_PCM_TRIGGER_SUSPEND:
>>> +        type = XENSND_OP_TRIGGER_PAUSE;
>>> +        break;
>>> +
>>> +    default:
>>> +        return -EINVAL;
>>> +    }
>>> +
>>> +    return xen_snd_front_stream_trigger(&stream->evt_pair->req, type);
>>> +}
>>> +
>>> +void xen_snd_front_alsa_handle_cur_pos(struct xen_snd_front_evtchnl 
>>> *evtchnl,
>>> +                       u64 pos_bytes)
>>> +{
>>> +    struct snd_pcm_substream *substream = evtchnl->u.evt.substream;
>>> +    struct pcm_stream_info *stream = stream_get(substream);
>>> +    snd_pcm_uframes_t delta, new_hw_ptr, cur_frame;
>>> +
>>> +    cur_frame = bytes_to_frames(substream->runtime, pos_bytes);
>>> +
>>> +    delta = cur_frame - stream->be_cur_frame;
>>> +    stream->be_cur_frame = cur_frame;
>>> +
>>> +    new_hw_ptr = (snd_pcm_uframes_t)atomic_read(&stream->hw_ptr);
>>> +    new_hw_ptr = (new_hw_ptr + delta) % 
>>> substream->runtime->buffer_size;
>>> +    atomic_set(&stream->hw_ptr, (int)new_hw_ptr);
>>> +
>>> +    stream->out_frames += delta;
>>> +    if (stream->out_frames > substream->runtime->period_size) {
>>> +        stream->out_frames %= substream->runtime->period_size;
>>> +        snd_pcm_period_elapsed(substream);
>>> +    }
>>> +}
>>> +
>>> +static snd_pcm_uframes_t alsa_pointer(struct snd_pcm_substream 
>>> *substream)
>>> +{
>>> +    struct pcm_stream_info *stream = stream_get(substream);
>>> +
>>> +    return (snd_pcm_uframes_t)atomic_read(&stream->hw_ptr);
>>> +}
>>> +
>>> +static int alsa_pb_copy_user(struct snd_pcm_substream *substream,
>>> +                 int channel, unsigned long pos, void __user *src,
>>> +                 unsigned long count)
>>> +{
>>> +    struct pcm_stream_info *stream = stream_get(substream);
>>> +
>>> +    if (unlikely(pos + count > stream->sh_buf.buffer_sz))
>>> +        return -EINVAL;
>>> +
>>> +    if (copy_from_user(stream->sh_buf.buffer + pos, src, count))
>>> +        return -EFAULT;
>>> +
>>> +    return xen_snd_front_stream_write(&stream->evt_pair->req, pos, 
>>> count);
>>> +}
>>> +
>>> +static int alsa_pb_copy_kernel(struct snd_pcm_substream *substream,
>>> +                   int channel, unsigned long pos, void *src,
>>> +                   unsigned long count)
>>> +{
>>> +    struct pcm_stream_info *stream = stream_get(substream);
>>> +
>>> +    if (unlikely(pos + count > stream->sh_buf.buffer_sz))
>>> +        return -EINVAL;
>>> +
>>> +    memcpy(stream->sh_buf.buffer + pos, src, count);
>>> +
>>> +    return xen_snd_front_stream_write(&stream->evt_pair->req, pos, 
>>> count);
>>> +}
>>> +
>>> +static int alsa_cap_copy_user(struct snd_pcm_substream *substream,
>>> +                  int channel, unsigned long pos, void __user *dst,
>>> +                  unsigned long count)
>>> +{
>>> +    struct pcm_stream_info *stream = stream_get(substream);
>>> +    int ret;
>>> +
>>> +    if (unlikely(pos + count > stream->sh_buf.buffer_sz))
>>> +        return -EINVAL;
>>> +
>>> +    ret = xen_snd_front_stream_read(&stream->evt_pair->req, pos, 
>>> count);
>>> +    if (ret < 0)
>>> +        return ret;
>>> +
>>> +    return copy_to_user(dst, stream->sh_buf.buffer + pos, count) ?
>>> +        -EFAULT : 0;
>>> +}
>>> +
>>> +static int alsa_cap_copy_kernel(struct snd_pcm_substream *substream,
>>> +                int channel, unsigned long pos, void *dst,
>>> +                unsigned long count)
>>> +{
>>> +    struct pcm_stream_info *stream = stream_get(substream);
>>> +    int ret;
>>> +
>>> +    if (unlikely(pos + count > stream->sh_buf.buffer_sz))
>>> +        return -EINVAL;
>>> +
>>> +    ret = xen_snd_front_stream_read(&stream->evt_pair->req, pos, 
>>> count);
>>> +    if (ret < 0)
>>> +        return ret;
>>> +
>>> +    memcpy(dst, stream->sh_buf.buffer + pos, count);
>>> +
>>> +    return 0;
>>> +}
>>> +
>>> +static int alsa_pb_fill_silence(struct snd_pcm_substream *substream,
>>> +                int channel, unsigned long pos,
>>> +                unsigned long count)
>>> +{
>>> +    struct pcm_stream_info *stream = stream_get(substream);
>>> +
>>> +    if (unlikely(pos + count > stream->sh_buf.buffer_sz))
>>> +        return -EINVAL;
>>> +
>>> +    memset(stream->sh_buf.buffer + pos, 0, count);
>>> +
>>> +    return xen_snd_front_stream_write(&stream->evt_pair->req, pos, 
>>> count);
>>> +}
>>> +
>>> +/*
>>> + * FIXME: The mmaped data transfer is asynchronous and there is no
>>> + * ack signal from user-space when it is done. This is the
>>> + * reason it is not implemented in the PV driver as we do need
>>> + * to know when the buffer can be transferred to the backend.
>>> + */
>>> +
>>> +static struct snd_pcm_ops snd_drv_alsa_playback_ops = {
>>> +    .open = alsa_open,
>>> +    .close = alsa_close,
>>> +    .ioctl = snd_pcm_lib_ioctl,
>>> +    .hw_params = alsa_hw_params,
>>> +    .hw_free = alsa_hw_free,
>>> +    .prepare = alsa_prepare,
>>> +    .trigger = alsa_trigger,
>>> +    .pointer = alsa_pointer,
>>> +    .copy_user = alsa_pb_copy_user,
>>> +    .copy_kernel = alsa_pb_copy_kernel,
>>> +    .fill_silence = alsa_pb_fill_silence,
>>> +};
>>> +
>>> +static struct snd_pcm_ops snd_drv_alsa_capture_ops = {
>>> +    .open = alsa_open,
>>> +    .close = alsa_close,
>>> +    .ioctl = snd_pcm_lib_ioctl,
>>> +    .hw_params = alsa_hw_params,
>>> +    .hw_free = alsa_hw_free,
>>> +    .prepare = alsa_prepare,
>>> +    .trigger = alsa_trigger,
>>> +    .pointer = alsa_pointer,
>>> +    .copy_user = alsa_cap_copy_user,
>>> +    .copy_kernel = alsa_cap_copy_kernel,
>>> +};
>>> +
>>> +static int new_pcm_instance(struct card_info *card_info,
>>> +                struct xen_front_cfg_pcm_instance *instance_cfg,
>>> +                struct pcm_instance_info *pcm_instance_info)
>>> +{
>>> +    struct snd_pcm *pcm;
>>> +    int ret, i;
>>> +
>>> +    dev_dbg(&card_info->front_info->xb_dev->dev,
>>> +        "New PCM device \"%s\" with id %d playback %d capture %d",
>>> +        instance_cfg->name,
>>> +        instance_cfg->device_id,
>>> +        instance_cfg->num_streams_pb,
>>> +        instance_cfg->num_streams_cap);
>>> +
>>> +    pcm_instance_info->card_info = card_info;
>>> +
>>> +    pcm_instance_info->pcm_hw = instance_cfg->pcm_hw;
>>> +
>>> +    if (instance_cfg->num_streams_pb) {
>>> +        pcm_instance_info->streams_pb =
>>> + devm_kcalloc(&card_info->card->card_dev,
>>> +                         instance_cfg->num_streams_pb,
>>> +                         sizeof(struct pcm_stream_info),
>>> +                         GFP_KERNEL);
>>> +        if (!pcm_instance_info->streams_pb)
>>> +            return -ENOMEM;
>>> +    }
>>> +
>>> +    if (instance_cfg->num_streams_cap) {
>>> +        pcm_instance_info->streams_cap =
>>> + devm_kcalloc(&card_info->card->card_dev,
>>> +                         instance_cfg->num_streams_cap,
>>> +                         sizeof(struct pcm_stream_info),
>>> +                         GFP_KERNEL);
>>> +        if (!pcm_instance_info->streams_cap)
>>> +            return -ENOMEM;
>>> +    }
>>> +
>>> +    pcm_instance_info->num_pcm_streams_pb =
>>> +            instance_cfg->num_streams_pb;
>>> +    pcm_instance_info->num_pcm_streams_cap =
>>> +            instance_cfg->num_streams_cap;
>>> +
>>> +    for (i = 0; i < pcm_instance_info->num_pcm_streams_pb; i++) {
>>> +        pcm_instance_info->streams_pb[i].pcm_hw =
>>> +            instance_cfg->streams_pb[i].pcm_hw;
>>> +        pcm_instance_info->streams_pb[i].index =
>>> +            instance_cfg->streams_pb[i].index;
>>> +    }
>>> +
>>> +    for (i = 0; i < pcm_instance_info->num_pcm_streams_cap; i++) {
>>> +        pcm_instance_info->streams_cap[i].pcm_hw =
>>> +            instance_cfg->streams_cap[i].pcm_hw;
>>> +        pcm_instance_info->streams_cap[i].index =
>>> +            instance_cfg->streams_cap[i].index;
>>> +    }
>>> +
>>> +    ret = snd_pcm_new(card_info->card, instance_cfg->name,
>>> +              instance_cfg->device_id,
>>> +              instance_cfg->num_streams_pb,
>>> +              instance_cfg->num_streams_cap,
>>> +              &pcm);
>>> +    if (ret < 0)
>>> +        return ret;
>>> +
>>> +    pcm->private_data = pcm_instance_info;
>>> +    pcm->info_flags = 0;
>>> +    /* we want to handle all PCM operations in non-atomic context */
>>> +    pcm->nonatomic = true;
>>> +    strncpy(pcm->name, "Virtual card PCM", sizeof(pcm->name));
>>> +
>>> +    if (instance_cfg->num_streams_pb)
>>> +        snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_PLAYBACK,
>>> +                &snd_drv_alsa_playback_ops);
>>> +
>>> +    if (instance_cfg->num_streams_cap)
>>> +        snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_CAPTURE,
>>> +                &snd_drv_alsa_capture_ops);
>>> +
>>> +    pcm_instance_info->pcm = pcm;
>>> +    return 0;
>>> +}
>>> +
>>> +int xen_snd_front_alsa_init(struct xen_snd_front_info *front_info)
>>> +{
>>> +    struct device *dev = &front_info->xb_dev->dev;
>>> +    struct xen_front_cfg_card *cfg = &front_info->cfg;
>>> +    struct card_info *card_info;
>>> +    struct snd_card *card;
>>> +    int ret, i;
>>> +
>>> +    dev_dbg(dev, "Creating virtual sound card\n");
>>> +
>>> +    ret = snd_card_new(dev, 0, XENSND_DRIVER_NAME, THIS_MODULE,
>>> +               sizeof(struct card_info), &card);
>>> +    if (ret < 0)
>>> +        return ret;
>>> +
>>> +    card_info = card->private_data;
>>> +    card_info->front_info = front_info;
>>> +    front_info->card_info = card_info;
>>> +    card_info->card = card;
>>> +    card_info->pcm_instances =
>>> +            devm_kcalloc(dev, cfg->num_pcm_instances,
>>> +                     sizeof(struct pcm_instance_info),
>>> +                     GFP_KERNEL);
>>> +    if (!card_info->pcm_instances) {
>>> +        ret = -ENOMEM;
>>> +        goto fail;
>>> +    }
>>> +
>>> +    card_info->num_pcm_instances = cfg->num_pcm_instances;
>>> +    card_info->pcm_hw = cfg->pcm_hw;
>>> +
>>> +    for (i = 0; i < cfg->num_pcm_instances; i++) {
>>> +        ret = new_pcm_instance(card_info, &cfg->pcm_instances[i],
>>> +                       &card_info->pcm_instances[i]);
>>> +        if (ret < 0)
>>> +            goto fail;
>>> +    }
>>> +
>>> +    strncpy(card->driver, XENSND_DRIVER_NAME, sizeof(card->driver));
>>> +    strncpy(card->shortname, cfg->name_short, 
>>> sizeof(card->shortname));
>>> +    strncpy(card->longname, cfg->name_long, sizeof(card->longname));
>>> +
>>> +    ret = snd_card_register(card);
>>> +    if (ret < 0)
>>> +        goto fail;
>>> +
>>> +    return 0;
>>> +
>>> +fail:
>>> +    snd_card_free(card);
>>> +    return ret;
>>> +}
>>> +
>>> +void xen_snd_front_alsa_fini(struct xen_snd_front_info *front_info)
>>> +{
>>> +    struct card_info *card_info;
>>> +    struct snd_card *card;
>>> +
>>> +    card_info = front_info->card_info;
>>> +    if (!card_info)
>>> +        return;
>>> +
>>> +    card = card_info->card;
>>> +    if (!card)
>>> +        return;
>>> +
>>> +    dev_dbg(&front_info->xb_dev->dev, "Removing virtual sound card 
>>> %d\n",
>>> +        card->number);
>>> +    snd_card_free(card);
>>> +
>>> +    /* card_info will be freed when destroying 
>>> front_info->xb_dev->dev */
>>> +    card_info->card = NULL;
>>> +}
>>> diff --git a/sound/xen/xen_snd_front_alsa.h 
>>> b/sound/xen/xen_snd_front_alsa.h
>>> new file mode 100644
>>> index 000000000000..18abd9eec967
>>> --- /dev/null
>>> +++ b/sound/xen/xen_snd_front_alsa.h
>>> @@ -0,0 +1,23 @@
>>> +/* 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>
>>> + */
>>> +
>>> +#ifndef __XEN_SND_FRONT_ALSA_H
>>> +#define __XEN_SND_FRONT_ALSA_H
>>> +
>>> +struct xen_snd_front_info;
>>> +
>>> +int xen_snd_front_alsa_init(struct xen_snd_front_info *front_info);
>>> +
>>> +void xen_snd_front_alsa_fini(struct xen_snd_front_info *front_info);
>>> +
>>> +void xen_snd_front_alsa_handle_cur_pos(struct xen_snd_front_evtchnl 
>>> *evtchnl,
>>> +                       u64 pos_bytes);
>>> +
>>> +#endif /* __XEN_SND_FRONT_ALSA_H */
>>> diff --git a/sound/xen/xen_snd_front_evtchnl.c 
>>> b/sound/xen/xen_snd_front_evtchnl.c
>>> index 9ece39f938f8..470196518716 100644
>>> --- a/sound/xen/xen_snd_front_evtchnl.c
>>> +++ b/sound/xen/xen_snd_front_evtchnl.c
>>> @@ -14,6 +14,7 @@
>>>   #include <xen/xenbus.h>
>>>     #include "xen_snd_front.h"
>>> +#include "xen_snd_front_alsa.h"
>>>   #include "xen_snd_front_cfg.h"
>>>   #include "xen_snd_front_evtchnl.h"
>>>   @@ -111,7 +112,10 @@ static irqreturn_t evtchnl_interrupt_evt(int 
>>> irq, void *dev_id)
>>>             switch (event->type) {
>>>           case XENSND_EVT_CUR_POS:
>>> -            /* do nothing at the moment */
>>> + spin_unlock_irqrestore(&front_info->io_lock, flags);
>>> +            xen_snd_front_alsa_handle_cur_pos(channel,
>>> +                              event->op.cur_pos.position);
>>> +            spin_lock_irqsave(&front_info->io_lock, flags);
>> Is this correct? Why can you free the lock here without doing any
>> harm? What is the lock protecting? I'd like to see at least some
>> comments explaining why the lock is needed and why it can be dropped
>> here.
> Well, this code has issues and will be re-worked:
> 1. Which locks I need:
> 1.1. lock to serialize requests to backend
> 1.2. lock to protect the ring: between requests code and interrupt 
> handler
>
> 2. I don't really need a spinlock here b/c interrupts are threaded,
> so I can safely use a mutex: thus no need for fancy code with unlocking
> and locking again while servicing xen_snd_front_alsa_handle_cur_pos
>
> Thank you
>>
>> Juergen
>