Hello Luiz
Sender : Luiz Augusto von Dentz <luiz.dentz@xxxxxxxxx>
>Hi Nagaraj,
>On Wed, May 2, 2018 at 11:40 AM Nagaraj D R <nagaraj.dr@xxxxxxxxxxx> wrote:
>> For BREDR-ATT, according to spec, ATT MTU is same has
>> L2CAP configured MTU on which ATT is running. So, set the MTU to
>> L2CAP configuration and for LE-ATT adjust the ATT MTU based on
>> EXCHANGE_MTU request and response.
>> ---
>> src/device.c | 2 +-
>> src/shared/gatt-helpers.c | 1 +
>> 2 files changed, 2 insertions(+), 1 deletion(-)
>> diff --git a/src/device.c b/src/device.c
>> index f693b70..cf4c8df 100644
>> --- a/src/device.c
>> +++ b/src/device.c
>> @@ -4922,7 +4922,7 @@ bool device_attach_att(struct btd_device *dev,
GIOChannel *io)
>> }
>> dev->att_mtu = MIN(mtu, BT_ATT_MAX_LE_MTU);
>> - attrib = g_attrib_new(io, BT_ATT_DEFAULT_LE_MTU, false);
>> + attrib = g_attrib_new(io, dev->att_mtu, false);
>This would actually undo the following patch:
> src/device: Use BT_ATT_DEFAULT_LE_MTU as default MTU
> Use the default MTU until an MTU exchange has taken place and
> something else has been negotiated. If either side does not support
> MTU exchange, the connection shall continue to use this default
> value instead of the device maximum which was the previous behavior.
>We should probably check if the cid is for LE or not and reset mtu to
>BT_ATT_DEFAULT_LE_MTU that way att_mtu should be valid for either LE or
>BR/EDR.
I agree, we should check for CID.
If it is BREDR-ATT connection only then consider L2CAP MTU otherwise
set the MTU to min value and set it through ATT_MTU exchange.
>> if (!attrib) {
>> error("Unable to create new GAttrib instance");
>> return false;
>> diff --git a/src/shared/gatt-helpers.c b/src/shared/gatt-helpers.c
>> index 6b39bb1..8ec65be 100644
>> --- a/src/shared/gatt-helpers.c
>> +++ b/src/shared/gatt-helpers.c
>> @@ -517,6 +517,7 @@ static void mtu_cb(uint8_t opcode, const void *pdu,
uint16_t length,
>> if (opcode == BT_ATT_OP_ERROR_RSP) {
>> success = false;
>> att_ecode = process_error(pdu, length);
>> + bt_att_set_mtu(op->att, BT_ATT_DEFAULT_LE_MTU);
>I not following this one, we only really use bt_att_set_mtu if the command
>succeeds so this should not be necessary, or this is due Exchange being
>used multiple times? I recall the spec not allowing that to happen, and if
>does Im not sure why we would have to return to the default instead of the
>value previously set in case the of error response.
This change was in connection with my proposed change.
i.e We set the MTU to L2CAP-MTU (for both LE-ATT and BREDR-ATT)
In case of LE-ATT, if remote does not support the ATT-MTU exchange procedure,
then it will return "BT_ATT_OP_ERROR_RSP" and we will fall back to default-MTU
With CID check that you advised, this change won't be necessary.
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