Hi Marijn, On Tue, Oct 19, 2021 at 2:17 AM Marijn Suijten <marijn.suijten@xxxxxxxxxxxxxx> wrote: > > The AVRCP spec (1.6.2) does not mention anything about a version > requirement for Absolute Volume, despite this feature only existing > since spec version 1.4. Android reports a version of 1.3 [1] for its > "AVRCP remote" (CT) service and mentions in the comment above it itself > relies on feature bits rather than the exposed version. As it stands > BlueZ requires at least version 1.4 making it unable to communicate > absolute volume levels with even the most recent Android phones running > Fluoride (have not checked the version on Gabeldorsche). > > The spec states that supporting SetAbsoluteVolume and > EVENT_VOLUME_CHANGED are mandatory when feature level 2 is declared, > excluded otherwise. This feature bit is set on Android and, when used > by this patch, allows for successfully communicating volume back and > forth despite the version theoretically being too low. > > [1]: https://android.googlesource.com/platform/system/bt/+/android-11.0.0_r28/bta/av/bta_av_main.cc#761 But I don't think this is valid, if EVENT_VOLUME_CHANGED was introduced in 1.4 it should have been a reserved value in 1.3 so it cannot be used. So Android should really report 1.4 on its controller record, have you tried submitting a patch to Android to change it to report the version as 1.4? Anyway I'd only adopt such a change if we could identify the remote end is Android otherwise we risk IOP issues by reporting a value that is considered reserved with other stacks. > --- > > Changes since v1: > - Use block comment intead of single-line comment. > > profiles/audio/avrcp.c | 8 ++++++-- > 1 file changed, 6 insertions(+), 2 deletions(-) > > diff --git a/profiles/audio/avrcp.c b/profiles/audio/avrcp.c > index d3c9cb795..e530eeab4 100644 > --- a/profiles/audio/avrcp.c > +++ b/profiles/audio/avrcp.c > @@ -4175,13 +4175,17 @@ static void target_init(struct avrcp *session) > (1 << AVRCP_EVENT_TRACK_REACHED_END) | > (1 << AVRCP_EVENT_SETTINGS_CHANGED); > > + /* Remote device supports receiving volume notifications */ > + if (target->features & AVRCP_FEATURE_CATEGORY_2) > + session->supported_events |= > + (1 << AVRCP_EVENT_VOLUME_CHANGED); > + > if (target->version < 0x0104) > return; > > session->supported_events |= > (1 << AVRCP_EVENT_ADDRESSED_PLAYER_CHANGED) | > - (1 << AVRCP_EVENT_AVAILABLE_PLAYERS_CHANGED) | > - (1 << AVRCP_EVENT_VOLUME_CHANGED); > + (1 << AVRCP_EVENT_AVAILABLE_PLAYERS_CHANGED); > > /* Only check capabilities if controller is not supported */ > if (session->controller == NULL) > -- > 2.33.1 > -- Luiz Augusto von Dentz
