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From:   Luiz Augusto von Dentz <luiz.dentz@gmail.com>
Date:   Mon, 8 Jun 2020 13:28:37 -0700
Message-ID: <CABBYNZJNoiEdt2yi3CFbELRGRFrH+SwGzbnwXM_8OO=fattfZg@mail.gmail.com>
Subject: Re: Should we disable ERTM as default?
To:     Yun-hao Chung <howardchung@google.com>
Cc:     Marcel Holtmann <marcel@holtmann.org>,
        Bluez mailing list <linux-bluetooth@vger.kernel.org>
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Hi Yun-hao,

On Mon, Jun 8, 2020 at 9:15 AM Luiz Augusto von Dentz
<luiz.dentz@gmail.com> wrote:
>
> Hi Yun-hao,
>
> On Mon, Jun 8, 2020 at 6:11 AM Yun-hao Chung <howardchung@google.com> wro=
te:
> >
> > Hi Marcel,
> >
> > Here is the piece of the btmon trace.  What should be the next step?
> >
> > < ACL Data TX: Handle 256 flags 0x00 dlen 6
> >       Channel: 66 len 2 [PSM 25 mode Basic (0x00)] {chan 2}
> >       AVDTP: Discover (0x01) Command (0x00) type 0x00 label 3 nosp 0
> > > HCI Event: Number of Completed Packets (0x13) plen 5
> >         Num handles: 1
> >         Handle: 256
> >         Count: 1
> > > HCI Event: Number of Completed Packets (0x13) plen 5
> >         Num handles: 1
> >         Handle: 256
> >         Count: 1
> > > ACL Data RX: Handle 256 flags 0x02 dlen 8
> >       Channel: 66 len 4 [PSM 25 mode Basic (0x00)] {chan 2}
> >       AVDTP: Discover (0x01) Response Accept (0x02) type 0x00 label 3 n=
osp 0
> >         ACP SEID: 1
> >           Media Type: Audio (0x00)
> >           SEP Type: SNK (0x01)
> >           In use: No
> > < ACL Data TX: Handle 256 flags 0x00 dlen 18
> >       Channel: 66 len 14 [PSM 25 mode Basic (0x00)] {chan 2}
> >       AVDTP: Set Configuration (0x03) Command (0x00) type 0x00 label 4 =
nosp 0
> >         ACP SEID: 1
> >         INT SEID: 1
> >         Service Category: Media Transport (0x01)
> >         Service Category: Media Codec (0x07)
> >           Media Type: Audio (0x00)
> >           Media Codec: SBC (0x00)
> >             Frequency: 48000 (0x10)
> >             Channel Mode: Joint Stereo (0x01)
> >             Block Length: 16 (0x10)
> >             Subbands: 8 (0x04)
> >             Allocation Method: Loudness (0x01)
> >             Minimum Bitpool: 2
> >             Maximum Bitpool: 64
> > > HCI Event: Number of Completed Packets (0x13) plen 5
> >         Num handles: 1
> >         Handle: 256
> >         Count: 1
> > > ACL Data RX: Handle 256 flags 0x02 dlen 6
> >       Channel: 66 len 2 [PSM 25 mode Basic (0x00)] {chan 2}
> >       AVDTP: Set Configuration (0x03) Response Accept (0x02) type 0x00 =
label 4 nosp 0
> > < ACL Data TX: Handle 256 flags 0x00 dlen 7
> >       Channel: 66 len 3 [PSM 25 mode Basic (0x00)] {chan 2}
> >       AVDTP: Open (0x06) Command (0x00) type 0x00 label 5 nosp 0
> >         ACP SEID: 1
> > > HCI Event: Number of Completed Packets (0x13) plen 5
> >         Num handles: 1
> >         Handle: 256
> >         Count: 1
> > > ACL Data RX: Handle 256 flags 0x02 dlen 6
> >       Channel: 66 len 2 [PSM 25 mode Basic (0x00)] {chan 2}
> >       AVDTP: Open (0x06) Response Accept (0x02) type 0x00 label 5 nosp =
0
> > < ACL Data TX: Handle 256 flags 0x00 dlen 12
> >       L2CAP: Connection Request (0x02) ident 6 len 4
> >         PSM: 25 (0x0019)
> >         Source CID: 67
> > > HCI Event: Number of Completed Packets (0x13) plen 5
> >         Num handles: 1
> >         Handle: 256
> >         Count: 1
> > > ACL Data RX: Handle 256 flags 0x02 dlen 16
> >       L2CAP: Connection Response (0x03) ident 6 len 8
> >         Destination CID: 67
> >         Source CID: 67
> >         Result: Connection pending (0x0001)
> >         Status: No further information available (0x0000)
> > > ACL Data RX: Handle 256 flags 0x02 dlen 16
> >       L2CAP: Connection Response (0x03) ident 6 len 8
> >         Destination CID: 67
> >         Source CID: 67
> >         Result: Connection successful (0x0000)
> >         Status: No further information available (0x0000)
> > < ACL Data TX: Handle 256 flags 0x00 dlen 23
> >       L2CAP: Configure Request (0x04) ident 7 len 15
> >         Destination CID: 67
> >         Flags: 0x0000
> >         Option: Retransmission and Flow Control (0x04) [mandatory]
> >           Mode: Basic (0x00)
> >           TX window size: 0
> >           Max transmit: 0
> >           Retransmission timeout: 0
> >           Monitor timeout: 0
> >           Maximum PDU size: 0
> > > ACL Data RX: Handle 256 flags 0x02 dlen 23
> >       L2CAP: Configure Request (0x04) ident 222 len 15
> >         Destination CID: 67
> >         Flags: 0x0000
> >         Option: Retransmission and Flow Control (0x04) [mandatory]
> >           Mode: Streaming (0x04)
>
> Looks like we should be using BT_IO_MODE_STREAMING with MPS then.
>
> >           TX window size: 0
> >           Max transmit: 0
> >           Retransmission timeout: 0
> >           Monitor timeout: 0
> >           Maximum PDU size: 672
> > < ACL Data TX: Handle 256 flags 0x00 dlen 25
> >       L2CAP: Configure Response (0x05) ident 222 len 17
> >         Source CID: 67
> >         Flags: 0x0000
> >         Result: Failure - unacceptable parameters (0x0001)
> >         Option: Retransmission and Flow Control (0x04) [mandatory]
> >           Mode: Basic (0x00)
> >           TX window size: 0
> >           Max transmit: 0
> >           Retransmission timeout: 0
> >           Monitor timeout: 0
> >           Maximum PDU size: 672
> > > HCI Event: Number of Completed Packets (0x13) plen 5
> >         Num handles: 1
> >         Handle: 256
> >         Count: 1
> > > HCI Event: Number of Completed Packets (0x13) plen 5
> >         Num handles: 1
> >         Handle: 256
> >         Count: 1
> > > ACL Data RX: Handle 256 flags 0x02 dlen 29
> >       L2CAP: Configure Response (0x05) ident 7 len 21
> >         Source CID: 67
> >         Flags: 0x0000
> >         Result: Success (0x0000)
> >         Option: Maximum Transmission Unit (0x01) [mandatory]
> >           MTU: 672
> >         Option: Retransmission and Flow Control (0x04) [mandatory]
> >           Mode: Basic (0x00)
> >           TX window size: 0
> >           Max transmit: 0
> >           Retransmission timeout: 0
> >           Monitor timeout: 0
> >           Maximum PDU size: 0
> > > ACL Data RX: Handle 256 flags 0x02 dlen 12
> >       L2CAP: Configure Request (0x04) ident 223 len 4
> >         Destination CID: 67
> >         Flags: 0x0000
> > < ACL Data TX: Handle 256 flags 0x00 dlen 18
> >       L2CAP: Configure Response (0x05) ident 223 len 10
> >         Source CID: 67
> >         Flags: 0x0000
> >         Result: Success (0x0000)
> >         Option: Maximum Transmission Unit (0x01) [mandatory]
> >           MTU: 672
> >
> > Thanks.
> >
> > On Mon, Jun 8, 2020 at 3:58 PM Marcel Holtmann <marcel@holtmann.org> wr=
ote:
> >>
> >> Hi Yun-hao,
> >>
> >> > I think it is more likely to be the PTS's limitations. I realized th=
e
> >> > problem is in the media channel not in the signaling channel. PTS
> >> > wants to use streaming mode, but bluez rejects it, and then PTS abor=
ts
> >> > the test. According to the MPS 1.0 Spec 6.2, L2CAP streaming mode is
> >> > the recommendation for optimization when using MPS media control
> >> > channels, so I think bluez doesn't do anything wrong during this tes=
t.
> >>
> >> do you have the btmon trace for this. I think we should accept ERTM on=
 the media channel. The unfortunate part is that control and media channels=
 both use PSM 25 and so we can=E2=80=99t be really selective when we are th=
e acceptor. If MPS wants us to accept ERTM on the media channel we should a=
llow. For all I care we can even accept it on the control channel, but it i=
s just a waste of overhead on the L2CAP headers. Actually the new Enhanced =
Flow Control mode on BR/EDR would be more efficient for A2DP.
>
> Perhaps we can default to Streaming mode if MPS is enabled, we could
> actually do use it only for the transport channel while initiating but
> as a receiver I don't think it is possible to change after listen.

I've sent a patch implementing this, let me know if that works with PTS.

--=20
Luiz Augusto von Dentz