2021-06-07 20:40:56

by Sonny Sasaka

[permalink] [raw]
Subject: [PATCH BlueZ] Queue SetAbsoluteVolume if there is an in-progress one.

SetAbsoluteVolume command may receive late response for Target Device
that have high latency processing. In that case we may send the next
SetAbsoluteVolume commands before the previous SetAbsoluteVolume
response is received. This causes the media transport volume to jitter.

The solution in this patch is to not send any SetAbsoluteVolume command
if there is an in-progress one. Instead we should queue this command to
be executed after the in-progress one receives the response.

Reviewed-by: Archie Pusaka <[email protected]>
Reviewed-by: Miao-chen Chou <[email protected]>

---
profiles/audio/avrcp.c | 49 ++++++++++++++++++++++++++++++++++++++++++
1 file changed, 49 insertions(+)

diff --git a/profiles/audio/avrcp.c b/profiles/audio/avrcp.c
index ccf34b220..c6946dc46 100644
--- a/profiles/audio/avrcp.c
+++ b/profiles/audio/avrcp.c
@@ -256,6 +256,11 @@ struct avrcp_data {
GSList *players;
};

+struct set_volume_command {
+ uint8_t volume;
+ bool notify;
+};
+
struct avrcp {
struct avrcp_server *server;
struct avctp *conn;
@@ -275,6 +280,12 @@ struct avrcp {
uint8_t transaction;
uint8_t transaction_events[AVRCP_EVENT_LAST + 1];
struct pending_pdu *pending_pdu;
+ // Whether there is a SetAbsoluteVolume command that is still waiting
+ // for response.
+ bool is_set_volume_in_progress;
+ // If this is non-null, then we need to issue SetAbsoluteVolume
+ // after the current in-progress SetAbsoluteVolume receives response.
+ struct set_volume_command *queued_set_volume;
};

struct passthrough_handler {
@@ -4252,6 +4263,24 @@ static void target_destroy(struct avrcp *session)
g_free(target);
}

+void update_queued_set_volume(struct avrcp *session, uint8_t volume,
+ bool notify)
+{
+ if (!session->queued_set_volume)
+ session->queued_set_volume = g_new0(struct set_volume_command,
+ 1);
+ session->queued_set_volume->volume = volume;
+ session->queued_set_volume->notify = notify;
+}
+
+void clear_queued_set_volume(struct avrcp *session)
+{
+ if (!session->queued_set_volume)
+ return;
+ g_free(session->queued_set_volume);
+ session->queued_set_volume = NULL;
+}
+
static void session_destroy(struct avrcp *session, int err)
{
struct avrcp_server *server = session->server;
@@ -4295,6 +4324,8 @@ static void session_destroy(struct avrcp *session, int err)
if (session->browsing_id > 0)
avctp_unregister_browsing_pdu_handler(session->browsing_id);

+ clear_queued_set_volume(session);
+
g_free(session);
}

@@ -4486,6 +4517,8 @@ static gboolean avrcp_handle_set_volume(struct avctp *conn, uint8_t code,
struct avrcp_header *pdu = (void *) operands;
int8_t volume;

+ session->is_set_volume_in_progress = false;
+
if (code == AVC_CTYPE_REJECTED || code == AVC_CTYPE_NOT_IMPLEMENTED ||
pdu == NULL)
return FALSE;
@@ -4495,6 +4528,13 @@ static gboolean avrcp_handle_set_volume(struct avctp *conn, uint8_t code,
/* Always attempt to update the transport volume */
media_transport_update_device_volume(session->dev, volume);

+ if (session->queued_set_volume) {
+ avrcp_set_volume(session->dev,
+ session->queued_set_volume->volume,
+ session->queued_set_volume->notify);
+ clear_queued_set_volume(session);
+ }
+
if (player != NULL)
player->cb->set_volume(volume, session->dev, player->user_data);

@@ -4570,6 +4610,14 @@ int avrcp_set_volume(struct btd_device *dev, int8_t volume, bool notify)
if (session == NULL)
return -ENOTCONN;

+ // If there is an in-progress SetAbsoluteVolume, just update the
+ // queued_set_volume. Once the in-progress SetAbsoluteVolume receives
+ // response, it will send the queued SetAbsoluteVolume command.
+ if (session->is_set_volume_in_progress) {
+ update_queued_set_volume(session, volume, notify);
+ return 0;
+ }
+
if (notify) {
if (!session->target)
return -ENOTSUP;
@@ -4589,6 +4637,7 @@ int avrcp_set_volume(struct btd_device *dev, int8_t volume, bool notify)
pdu->params[0] = volume;
pdu->params_len = htons(1);

+ session->is_set_volume_in_progress = TRUE;
return avctp_send_vendordep_req(session->conn,
AVC_CTYPE_CONTROL, AVC_SUBUNIT_PANEL,
buf, sizeof(buf),
--
2.31.0


2021-06-07 21:18:52

by Luiz Augusto von Dentz

[permalink] [raw]
Subject: Re: [PATCH BlueZ] Queue SetAbsoluteVolume if there is an in-progress one.

Hi Sonny,

On Mon, Jun 7, 2021 at 1:40 PM Sonny Sasaka <[email protected]> wrote:
>
> SetAbsoluteVolume command may receive late response for Target Device
> that have high latency processing. In that case we may send the next
> SetAbsoluteVolume commands before the previous SetAbsoluteVolume
> response is received. This causes the media transport volume to jitter.

You have to explain better what is the situation here, does the upper
layer queue several volume changes in a row and why? If this is coming
from different entities then there is obviously a conflict, but I
think we only allow the volume to changed from the entity that is
handling the A2DP stream.

> The solution in this patch is to not send any SetAbsoluteVolume command
> if there is an in-progress one. Instead we should queue this command to
> be executed after the in-progress one receives the response.
>
> Reviewed-by: Archie Pusaka <[email protected]>
> Reviewed-by: Miao-chen Chou <[email protected]>
>
> ---
> profiles/audio/avrcp.c | 49 ++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 49 insertions(+)
>
> diff --git a/profiles/audio/avrcp.c b/profiles/audio/avrcp.c
> index ccf34b220..c6946dc46 100644
> --- a/profiles/audio/avrcp.c
> +++ b/profiles/audio/avrcp.c
> @@ -256,6 +256,11 @@ struct avrcp_data {
> GSList *players;
> };
>
> +struct set_volume_command {
> + uint8_t volume;
> + bool notify;
> +};
> +
> struct avrcp {
> struct avrcp_server *server;
> struct avctp *conn;
> @@ -275,6 +280,12 @@ struct avrcp {
> uint8_t transaction;
> uint8_t transaction_events[AVRCP_EVENT_LAST + 1];
> struct pending_pdu *pending_pdu;
> + // Whether there is a SetAbsoluteVolume command that is still waiting
> + // for response.
> + bool is_set_volume_in_progress;
> + // If this is non-null, then we need to issue SetAbsoluteVolume
> + // after the current in-progress SetAbsoluteVolume receives response.
> + struct set_volume_command *queued_set_volume;
> };
>
> struct passthrough_handler {
> @@ -4252,6 +4263,24 @@ static void target_destroy(struct avrcp *session)
> g_free(target);
> }
>
> +void update_queued_set_volume(struct avrcp *session, uint8_t volume,
> + bool notify)
> +{
> + if (!session->queued_set_volume)
> + session->queued_set_volume = g_new0(struct set_volume_command,
> + 1);
> + session->queued_set_volume->volume = volume;
> + session->queued_set_volume->notify = notify;
> +}
> +
> +void clear_queued_set_volume(struct avrcp *session)
> +{
> + if (!session->queued_set_volume)
> + return;
> + g_free(session->queued_set_volume);
> + session->queued_set_volume = NULL;
> +}
> +
> static void session_destroy(struct avrcp *session, int err)
> {
> struct avrcp_server *server = session->server;
> @@ -4295,6 +4324,8 @@ static void session_destroy(struct avrcp *session, int err)
> if (session->browsing_id > 0)
> avctp_unregister_browsing_pdu_handler(session->browsing_id);
>
> + clear_queued_set_volume(session);
> +
> g_free(session);
> }
>
> @@ -4486,6 +4517,8 @@ static gboolean avrcp_handle_set_volume(struct avctp *conn, uint8_t code,
> struct avrcp_header *pdu = (void *) operands;
> int8_t volume;
>
> + session->is_set_volume_in_progress = false;

I rather have a volume and volume_pending with the respectively
current volume and volume change in progress, if notification comes
with volume_pending then we are done otherwise we need to send another
command, only the last volume_pending is tracked so we don't have to
queue anything since changes done in between would be override only
the last volume change matters.

> if (code == AVC_CTYPE_REJECTED || code == AVC_CTYPE_NOT_IMPLEMENTED ||
> pdu == NULL)
> return FALSE;
> @@ -4495,6 +4528,13 @@ static gboolean avrcp_handle_set_volume(struct avctp *conn, uint8_t code,
> /* Always attempt to update the transport volume */
> media_transport_update_device_volume(session->dev, volume);
>
> + if (session->queued_set_volume) {
> + avrcp_set_volume(session->dev,
> + session->queued_set_volume->volume,
> + session->queued_set_volume->notify);
> + clear_queued_set_volume(session);
> + }

Here it would be something like:

if (session->volume_pending != -1) {
if (session->volume_pending != volume)
avrcp_set_volume(session->dev, session->volume_pending, true);
else
session->volume_pending = -1;
}

Though there is a problem with the above, if for some odd reason the
device don't notify the exact volume we requested this will lead the
an endless loop since the volume would never match.

> +
> if (player != NULL)
> player->cb->set_volume(volume, session->dev, player->user_data);
>
> @@ -4570,6 +4610,14 @@ int avrcp_set_volume(struct btd_device *dev, int8_t volume, bool notify)
> if (session == NULL)
> return -ENOTCONN;
>
> + // If there is an in-progress SetAbsoluteVolume, just update the
> + // queued_set_volume. Once the in-progress SetAbsoluteVolume receives
> + // response, it will send the queued SetAbsoluteVolume command.
> + if (session->is_set_volume_in_progress) {

Let do something like the following:

if (session->volume_pending != -1 && session->volume_pending != volume) {
session->volume_pending = value;
return 0;
}

> + update_queued_set_volume(session, volume, notify);
> + return 0;
> + }
> +
> if (notify) {
> if (!session->target)
> return -ENOTSUP;
> @@ -4589,6 +4637,7 @@ int avrcp_set_volume(struct btd_device *dev, int8_t volume, bool notify)
> pdu->params[0] = volume;
> pdu->params_len = htons(1);
>
> + session->is_set_volume_in_progress = TRUE;
> return avctp_send_vendordep_req(session->conn,
> AVC_CTYPE_CONTROL, AVC_SUBUNIT_PANEL,
> buf, sizeof(buf),
> --
> 2.31.0
>


--
Luiz Augusto von Dentz

2021-06-07 22:56:28

by Marijn Suijten

[permalink] [raw]
Subject: Re: [PATCH BlueZ] Queue SetAbsoluteVolume if there is an in-progress one.

Hi Luiz, Sonny,

On 6/7/21 11:16 PM, Luiz Augusto von Dentz wrote:
> Hi Sonny,
>
> On Mon, Jun 7, 2021 at 1:40 PM Sonny Sasaka <[email protected]> wrote:
>>
>> SetAbsoluteVolume command may receive late response for Target Device
>> that have high latency processing. In that case we may send the next
>> SetAbsoluteVolume commands before the previous SetAbsoluteVolume
>> response is received. This causes the media transport volume to jitter.
>
> You have to explain better what is the situation here, does the upper
> layer queue several volume changes in a row and why? If this is coming
> from different entities then there is obviously a conflict, but I
> think we only allow the volume to changed from the entity that is
> handling the A2DP stream.


We've been running into a similar issue with PulseAudio. There is no
way to track a Set call for the Volume property back to the
property-change notification, running into both jitter on quick
successive volume changes and the inability to reflect peer hardware
volume in case the peer rounds the requested volume to a coarser scale.
This rounded value is supposedly returned from SetAbsoluteVolume
according to AVRCP spec 1.6.2, section 6.13.2:

The volume level which has actually been set on the TG is returned in
the response.

I would have proposed a new DBUS function SetAbsoluteVolume that accepts
volume as sole argument, blocks until the peer replies, and returns the
actual volume as per its namesake AVRCP command. This should address
both issues.

Note that it is also impossible to distinguish Volume property changes
from an action invoked on the peer (ie. the user pressing physical
buttons or using a volume slider on headphones) or the result of an
earlier Set(Volume) call as these to my knowledge all happen async, may
be intertwined, may involve rounding (on the peer) to make the resulting
number different, etc.

>
>> The solution in this patch is to not send any SetAbsoluteVolume command
>> if there is an in-progress one. Instead we should queue this command to
>> be executed after the in-progress one receives the response.
>>
>> Reviewed-by: Archie Pusaka <[email protected]>
>> Reviewed-by: Miao-chen Chou <[email protected]>
>>
>> ---
>> profiles/audio/avrcp.c | 49 ++++++++++++++++++++++++++++++++++++++++++
>> 1 file changed, 49 insertions(+)
>>
>> diff --git a/profiles/audio/avrcp.c b/profiles/audio/avrcp.c
>> index ccf34b220..c6946dc46 100644
>> --- a/profiles/audio/avrcp.c
>> +++ b/profiles/audio/avrcp.c
>> @@ -256,6 +256,11 @@ struct avrcp_data {
>> GSList *players;
>> };
>>
>> +struct set_volume_command {
>> + uint8_t volume;
>> + bool notify;
>> +};
>> +
>> struct avrcp {
>> struct avrcp_server *server;
>> struct avctp *conn;
>> @@ -275,6 +280,12 @@ struct avrcp {
>> uint8_t transaction;
>> uint8_t transaction_events[AVRCP_EVENT_LAST + 1];
>> struct pending_pdu *pending_pdu;
>> + // Whether there is a SetAbsoluteVolume command that is still waiting
>> + // for response.
>> + bool is_set_volume_in_progress;
>> + // If this is non-null, then we need to issue SetAbsoluteVolume
>> + // after the current in-progress SetAbsoluteVolume receives response.
>> + struct set_volume_command *queued_set_volume;
>> };
>>
>> struct passthrough_handler {
>> @@ -4252,6 +4263,24 @@ static void target_destroy(struct avrcp *session)
>> g_free(target);
>> }
>>
>> +void update_queued_set_volume(struct avrcp *session, uint8_t volume,
>> + bool notify)
>> +{
>> + if (!session->queued_set_volume)
>> + session->queued_set_volume = g_new0(struct set_volume_command,
>> + 1);
>> + session->queued_set_volume->volume = volume;
>> + session->queued_set_volume->notify = notify;
>> +}
>> +
>> +void clear_queued_set_volume(struct avrcp *session)
>> +{
>> + if (!session->queued_set_volume)
>> + return;
>> + g_free(session->queued_set_volume);
>> + session->queued_set_volume = NULL;
>> +}
>> +
>> static void session_destroy(struct avrcp *session, int err)
>> {
>> struct avrcp_server *server = session->server;
>> @@ -4295,6 +4324,8 @@ static void session_destroy(struct avrcp *session, int err)
>> if (session->browsing_id > 0)
>> avctp_unregister_browsing_pdu_handler(session->browsing_id);
>>
>> + clear_queued_set_volume(session);
>> +
>> g_free(session);
>> }
>>
>> @@ -4486,6 +4517,8 @@ static gboolean avrcp_handle_set_volume(struct avctp *conn, uint8_t code,
>> struct avrcp_header *pdu = (void *) operands;
>> int8_t volume;
>>
>> + session->is_set_volume_in_progress = false;
>
> I rather have a volume and volume_pending with the respectively
> current volume and volume change in progress, if notification comes
> with volume_pending then we are done otherwise we need to send another
> command, only the last volume_pending is tracked so we don't have to
> queue anything since changes done in between would be override only
> the last volume change matters.
>
>> if (code == AVC_CTYPE_REJECTED || code == AVC_CTYPE_NOT_IMPLEMENTED ||
>> pdu == NULL)
>> return FALSE;
>> @@ -4495,6 +4528,13 @@ static gboolean avrcp_handle_set_volume(struct avctp *conn, uint8_t code,
>> /* Always attempt to update the transport volume */
>> media_transport_update_device_volume(session->dev, volume);
>>
>> + if (session->queued_set_volume) {
>> + avrcp_set_volume(session->dev,
>> + session->queued_set_volume->volume,
>> + session->queued_set_volume->notify);
>> + clear_queued_set_volume(session);
>> + }
>
> Here it would be something like:
>
> if (session->volume_pending != -1) {
> if (session->volume_pending != volume)
> avrcp_set_volume(session->dev, session->volume_pending, true);
> else
> session->volume_pending = -1;
> }
>
> Though there is a problem with the above, if for some odd reason the
> device don't notify the exact volume we requested this will lead the
> an endless loop since the volume would never match.
>
>> +
>> if (player != NULL)
>> player->cb->set_volume(volume, session->dev, player->user_data);
>>
>> @@ -4570,6 +4610,14 @@ int avrcp_set_volume(struct btd_device *dev, int8_t volume, bool notify)
>> if (session == NULL)
>> return -ENOTCONN;
>>
>> + // If there is an in-progress SetAbsoluteVolume, just update the
>> + // queued_set_volume. Once the in-progress SetAbsoluteVolume receives
>> + // response, it will send the queued SetAbsoluteVolume command.
>> + if (session->is_set_volume_in_progress) {
>
> Let do something like the following:
>
> if (session->volume_pending != -1 && session->volume_pending != volume) {
> session->volume_pending = value;
> return 0;
> }
>
>> + update_queued_set_volume(session, volume, notify);
>> + return 0;
>> + }
>> +
>> if (notify) {
>> if (!session->target)
>> return -ENOTSUP;
>> @@ -4589,6 +4637,7 @@ int avrcp_set_volume(struct btd_device *dev, int8_t volume, bool notify)
>> pdu->params[0] = volume;
>> pdu->params_len = htons(1);
>>
>> + session->is_set_volume_in_progress = TRUE;
>> return avctp_send_vendordep_req(session->conn,
>> AVC_CTYPE_CONTROL, AVC_SUBUNIT_PANEL,
>> buf, sizeof(buf),
>> --
>> 2.31.0
>>
>
>
> --
> Luiz Augusto von Dentz
>

- Marijn

2021-06-07 23:53:42

by Luiz Augusto von Dentz

[permalink] [raw]
Subject: Re: [PATCH BlueZ] Queue SetAbsoluteVolume if there is an in-progress one.

Hi Marijn,

On Mon, Jun 7, 2021 at 3:46 PM Marijn Suijten
<[email protected]> wrote:
>
> Hi Luiz, Sonny,
>
> On 6/7/21 11:16 PM, Luiz Augusto von Dentz wrote:
> > Hi Sonny,
> >
> > On Mon, Jun 7, 2021 at 1:40 PM Sonny Sasaka <[email protected]> wrote:
> >>
> >> SetAbsoluteVolume command may receive late response for Target Device
> >> that have high latency processing. In that case we may send the next
> >> SetAbsoluteVolume commands before the previous SetAbsoluteVolume
> >> response is received. This causes the media transport volume to jitter.
> >
> > You have to explain better what is the situation here, does the upper
> > layer queue several volume changes in a row and why? If this is coming
> > from different entities then there is obviously a conflict, but I
> > think we only allow the volume to changed from the entity that is
> > handling the A2DP stream.
>
>
> We've been running into a similar issue with PulseAudio. There is no
> way to track a Set call for the Volume property back to the
> property-change notification, running into both jitter on quick
> successive volume changes and the inability to reflect peer hardware
> volume in case the peer rounds the requested volume to a coarser scale.
> This rounded value is supposedly returned from SetAbsoluteVolume
> according to AVRCP spec 1.6.2, section 6.13.2:
>
> The volume level which has actually been set on the TG is returned in
> the response.
>
> I would have proposed a new DBUS function SetAbsoluteVolume that accepts
> volume as sole argument, blocks until the peer replies, and returns the
> actual volume as per its namesake AVRCP command. This should address
> both issues.
>
> Note that it is also impossible to distinguish Volume property changes
> from an action invoked on the peer (ie. the user pressing physical
> buttons or using a volume slider on headphones) or the result of an
> earlier Set(Volume) call as these to my knowledge all happen async, may
> be intertwined, may involve rounding (on the peer) to make the resulting
> number different, etc.

Yep, the volume may actually be rounded like you said, so Im not
really sure how we can queue because we will not be able to verify the
volume has been set properly, we could do a blocking call even in case
of setting as a property we only need to delay the call to
g_dbus_pending_property_success until we actually receive a response,
that said there maybe some impact on the user experience since if you
have the volume implemented with something like a slider it will not
move smoothly anymore, but I guess that is better than have it
flipping back and forth, well except that can still happens because
the volume can be changed on the device in the meantime but I guess
the client wont see those changes until the method returns if it is
blocking waiting for the reply, which means it will only see that the
value flipped to something else later when the signals are dispatched.

If you feel like that is acceptable I'm happy to review any patches in
that direction.

> >
> >> The solution in this patch is to not send any SetAbsoluteVolume command
> >> if there is an in-progress one. Instead we should queue this command to
> >> be executed after the in-progress one receives the response.
> >>
> >> Reviewed-by: Archie Pusaka <[email protected]>
> >> Reviewed-by: Miao-chen Chou <[email protected]>
> >>
> >> ---
> >> profiles/audio/avrcp.c | 49 ++++++++++++++++++++++++++++++++++++++++++
> >> 1 file changed, 49 insertions(+)
> >>
> >> diff --git a/profiles/audio/avrcp.c b/profiles/audio/avrcp.c
> >> index ccf34b220..c6946dc46 100644
> >> --- a/profiles/audio/avrcp.c
> >> +++ b/profiles/audio/avrcp.c
> >> @@ -256,6 +256,11 @@ struct avrcp_data {
> >> GSList *players;
> >> };
> >>
> >> +struct set_volume_command {
> >> + uint8_t volume;
> >> + bool notify;
> >> +};
> >> +
> >> struct avrcp {
> >> struct avrcp_server *server;
> >> struct avctp *conn;
> >> @@ -275,6 +280,12 @@ struct avrcp {
> >> uint8_t transaction;
> >> uint8_t transaction_events[AVRCP_EVENT_LAST + 1];
> >> struct pending_pdu *pending_pdu;
> >> + // Whether there is a SetAbsoluteVolume command that is still waiting
> >> + // for response.
> >> + bool is_set_volume_in_progress;
> >> + // If this is non-null, then we need to issue SetAbsoluteVolume
> >> + // after the current in-progress SetAbsoluteVolume receives response.
> >> + struct set_volume_command *queued_set_volume;
> >> };
> >>
> >> struct passthrough_handler {
> >> @@ -4252,6 +4263,24 @@ static void target_destroy(struct avrcp *session)
> >> g_free(target);
> >> }
> >>
> >> +void update_queued_set_volume(struct avrcp *session, uint8_t volume,
> >> + bool notify)
> >> +{
> >> + if (!session->queued_set_volume)
> >> + session->queued_set_volume = g_new0(struct set_volume_command,
> >> + 1);
> >> + session->queued_set_volume->volume = volume;
> >> + session->queued_set_volume->notify = notify;
> >> +}
> >> +
> >> +void clear_queued_set_volume(struct avrcp *session)
> >> +{
> >> + if (!session->queued_set_volume)
> >> + return;
> >> + g_free(session->queued_set_volume);
> >> + session->queued_set_volume = NULL;
> >> +}
> >> +
> >> static void session_destroy(struct avrcp *session, int err)
> >> {
> >> struct avrcp_server *server = session->server;
> >> @@ -4295,6 +4324,8 @@ static void session_destroy(struct avrcp *session, int err)
> >> if (session->browsing_id > 0)
> >> avctp_unregister_browsing_pdu_handler(session->browsing_id);
> >>
> >> + clear_queued_set_volume(session);
> >> +
> >> g_free(session);
> >> }
> >>
> >> @@ -4486,6 +4517,8 @@ static gboolean avrcp_handle_set_volume(struct avctp *conn, uint8_t code,
> >> struct avrcp_header *pdu = (void *) operands;
> >> int8_t volume;
> >>
> >> + session->is_set_volume_in_progress = false;
> >
> > I rather have a volume and volume_pending with the respectively
> > current volume and volume change in progress, if notification comes
> > with volume_pending then we are done otherwise we need to send another
> > command, only the last volume_pending is tracked so we don't have to
> > queue anything since changes done in between would be override only
> > the last volume change matters.
> >
> >> if (code == AVC_CTYPE_REJECTED || code == AVC_CTYPE_NOT_IMPLEMENTED ||
> >> pdu == NULL)
> >> return FALSE;
> >> @@ -4495,6 +4528,13 @@ static gboolean avrcp_handle_set_volume(struct avctp *conn, uint8_t code,
> >> /* Always attempt to update the transport volume */
> >> media_transport_update_device_volume(session->dev, volume);
> >>
> >> + if (session->queued_set_volume) {
> >> + avrcp_set_volume(session->dev,
> >> + session->queued_set_volume->volume,
> >> + session->queued_set_volume->notify);
> >> + clear_queued_set_volume(session);
> >> + }
> >
> > Here it would be something like:
> >
> > if (session->volume_pending != -1) {
> > if (session->volume_pending != volume)
> > avrcp_set_volume(session->dev, session->volume_pending, true);
> > else
> > session->volume_pending = -1;
> > }
> >
> > Though there is a problem with the above, if for some odd reason the
> > device don't notify the exact volume we requested this will lead the
> > an endless loop since the volume would never match.
> >
> >> +
> >> if (player != NULL)
> >> player->cb->set_volume(volume, session->dev, player->user_data);
> >>
> >> @@ -4570,6 +4610,14 @@ int avrcp_set_volume(struct btd_device *dev, int8_t volume, bool notify)
> >> if (session == NULL)
> >> return -ENOTCONN;
> >>
> >> + // If there is an in-progress SetAbsoluteVolume, just update the
> >> + // queued_set_volume. Once the in-progress SetAbsoluteVolume receives
> >> + // response, it will send the queued SetAbsoluteVolume command.
> >> + if (session->is_set_volume_in_progress) {
> >
> > Let do something like the following:
> >
> > if (session->volume_pending != -1 && session->volume_pending != volume) {
> > session->volume_pending = value;
> > return 0;
> > }
> >
> >> + update_queued_set_volume(session, volume, notify);
> >> + return 0;
> >> + }
> >> +
> >> if (notify) {
> >> if (!session->target)
> >> return -ENOTSUP;
> >> @@ -4589,6 +4637,7 @@ int avrcp_set_volume(struct btd_device *dev, int8_t volume, bool notify)
> >> pdu->params[0] = volume;
> >> pdu->params_len = htons(1);
> >>
> >> + session->is_set_volume_in_progress = TRUE;
> >> return avctp_send_vendordep_req(session->conn,
> >> AVC_CTYPE_CONTROL, AVC_SUBUNIT_PANEL,
> >> buf, sizeof(buf),
> >> --
> >> 2.31.0
> >>
> >
> >
> > --
> > Luiz Augusto von Dentz
> >
>
> - Marijn



--
Luiz Augusto von Dentz

2021-06-08 09:53:21

by Marijn Suijten

[permalink] [raw]
Subject: Re: [PATCH BlueZ] Queue SetAbsoluteVolume if there is an in-progress one.

Hi Luiz,

On 6/8/21 1:47 AM, Luiz Augusto von Dentz wrote:
> Hi Marijn,
>
[..]
>> We've been running into a similar issue with PulseAudio. There is no
>> way to track a Set call for the Volume property back to the
>> property-change notification, running into both jitter on quick
>> successive volume changes and the inability to reflect peer hardware
>> volume in case the peer rounds the requested volume to a coarser scale.
>> This rounded value is supposedly returned from SetAbsoluteVolume
>> according to AVRCP spec 1.6.2, section 6.13.2:
>>
>> The volume level which has actually been set on the TG is returned in
>> the response.
>>
>> I would have proposed a new DBUS function SetAbsoluteVolume that accepts
>> volume as sole argument, blocks until the peer replies, and returns the
>> actual volume as per its namesake AVRCP command. This should address
>> both issues.
>>
>> Note that it is also impossible to distinguish Volume property changes
>> from an action invoked on the peer (ie. the user pressing physical
>> buttons or using a volume slider on headphones) or the result of an
>> earlier Set(Volume) call as these to my knowledge all happen async, may
>> be intertwined, may involve rounding (on the peer) to make the resulting
>> number different, etc.
>
> Yep, the volume may actually be rounded like you said, so Im not
> really sure how we can queue because we will not be able to verify the
> volume has been set properly, we could do a blocking call even in case
> of setting as a property we only need to delay the call to
> g_dbus_pending_property_success until we actually receive a response,
> that said there maybe some impact on the user experience since if you
> have the volume implemented with something like a slider it will not
> move smoothly anymore, but I guess that is better than have it
> flipping back and forth, well except that can still happens because
> the volume can be changed on the device in the meantime but I guess
> the client wont see those changes until the method returns if it is
> blocking waiting for the reply, which means it will only see that the
> value flipped to something else later when the signals are dispatched.


The main use-case is software volume compensation for devices with
limited granularity, for which we need to know exactly what is replied
to AVRCP's SetAbsoluteVolume call. Delaying
g_dbus_pending_property_success will only block the call longer but
won't exactly let us know the resulting value. We can immediately Get
the new property after (or try and relate the change notification to
it), but there's nothing preventing a change on the device intervening.
In that case we should discard requested volume (on the host) and
software compensation, and take/display device volume as-is.
This seems unfortunate as the AVRCP spec provides exactly the
consistency we're looking for here.

As for user experience it seems acceptable to make such a call block
until the peer replies, if only for a much more predictable API. It is
then up to the caller (ie. PulseAudio) to deal with that by
disabling/blocking the slider, or scheduling the most recent volume
update to be sent as soon as a reply is received (the DBus call returns).

>
> If you feel like that is acceptable I'm happy to review any patches in
> that direction.
>

[..]

> --
> Luiz Augusto von Dentz
- Marijn

2021-06-08 18:46:52

by Sonny Sasaka

[permalink] [raw]
Subject: Re: [PATCH BlueZ] Queue SetAbsoluteVolume if there is an in-progress one.

Hi Marijn,

Thanks for your inputs. Having a separate SetAbsoluteVolume API that
blocks (until the peer acknowledges the change) is certainly more
featureful than this patch's approach, since the media player can
decide what to do with pending SetAbsoluteVolume calls and have the
flexibility to handle the situation. However, there is also a value in
the shorter term approach that this patch without any changes in the
media player part and has been tested to solve the janky slider issue
in Chrome OS. I believe that this would also solve PulseAudio's
similar janky slider issue for the short term.

If Marijn and Luiz are okay with the shorter term approach first, I
will continue updating this patch according to Luiz's comments, but
otherwise I will abandon this patch in favor of the separate
SetAbsoluteVolume API that Marijn will provide.

On Tue, Jun 8, 2021 at 2:50 AM Marijn Suijten
<[email protected]> wrote:
>
> Hi Luiz,
>
> On 6/8/21 1:47 AM, Luiz Augusto von Dentz wrote:
> > Hi Marijn,
> >
> [..]
> >> We've been running into a similar issue with PulseAudio. There is no
> >> way to track a Set call for the Volume property back to the
> >> property-change notification, running into both jitter on quick
> >> successive volume changes and the inability to reflect peer hardware
> >> volume in case the peer rounds the requested volume to a coarser scale.
> >> This rounded value is supposedly returned from SetAbsoluteVolume
> >> according to AVRCP spec 1.6.2, section 6.13.2:
> >>
> >> The volume level which has actually been set on the TG is returned in
> >> the response.
> >>
> >> I would have proposed a new DBUS function SetAbsoluteVolume that accepts
> >> volume as sole argument, blocks until the peer replies, and returns the
> >> actual volume as per its namesake AVRCP command. This should address
> >> both issues.
> >>
> >> Note that it is also impossible to distinguish Volume property changes
> >> from an action invoked on the peer (ie. the user pressing physical
> >> buttons or using a volume slider on headphones) or the result of an
> >> earlier Set(Volume) call as these to my knowledge all happen async, may
> >> be intertwined, may involve rounding (on the peer) to make the resulting
> >> number different, etc.
> >
> > Yep, the volume may actually be rounded like you said, so Im not
> > really sure how we can queue because we will not be able to verify the
> > volume has been set properly, we could do a blocking call even in case
> > of setting as a property we only need to delay the call to
> > g_dbus_pending_property_success until we actually receive a response,
> > that said there maybe some impact on the user experience since if you
> > have the volume implemented with something like a slider it will not
> > move smoothly anymore, but I guess that is better than have it
> > flipping back and forth, well except that can still happens because
> > the volume can be changed on the device in the meantime but I guess
> > the client wont see those changes until the method returns if it is
> > blocking waiting for the reply, which means it will only see that the
> > value flipped to something else later when the signals are dispatched.
>
>
> The main use-case is software volume compensation for devices with
> limited granularity, for which we need to know exactly what is replied
> to AVRCP's SetAbsoluteVolume call. Delaying
> g_dbus_pending_property_success will only block the call longer but
> won't exactly let us know the resulting value. We can immediately Get
> the new property after (or try and relate the change notification to
> it), but there's nothing preventing a change on the device intervening.
> In that case we should discard requested volume (on the host) and
> software compensation, and take/display device volume as-is.
> This seems unfortunate as the AVRCP spec provides exactly the
> consistency we're looking for here.
>
> As for user experience it seems acceptable to make such a call block
> until the peer replies, if only for a much more predictable API. It is
> then up to the caller (ie. PulseAudio) to deal with that by
> disabling/blocking the slider, or scheduling the most recent volume
> update to be sent as soon as a reply is received (the DBus call returns).
>
> >
> > If you feel like that is acceptable I'm happy to review any patches in
> > that direction.
> >
>
> [..]
>
> > --
> > Luiz Augusto von Dentz
> - Marijn