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Bluetooth: HCI: Reword BT_BUF_ACL_* description

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Some part of the descriptions were wrong. Also, the description of
`BT_BUF_ACL_RX_SIZE` was too verbose and no longer needed with the
updated L2CAP documentation.

Signed-off-by: Théo Battrel <theo.battrel@nordicsemi.no>
This commit is contained in:
Théo Battrel 2024-04-03 13:22:03 +02:00 • committed by Anas Nashif
commit 2e7befe240
1 changed files with 14 additions and 27 deletions
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41
subsys/bluetooth/common/Kconfig
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@ -14,13 +14,14 @@ config BT_BUF_ACL_TX_SIZE
help help
Maximum supported ACL size of data packets sent from the Host to the Maximum supported ACL size of data packets sent from the Host to the
Controller. This value does not include the HCI ACL header. Controller. This value does not include the HCI ACL header.
The Host will segment the data transmitted to the Controller so that
packets sent to the Controller will contain data up to this size.
In a combined build this value will be set in both the Host and the In a combined build this value will be set in both the Host and the
Controller. Controller.
In a Host-only build the Host will read the maximum ACL size supported In a Host-only build the Host will read the maximum ACL size supported
by the Controller and use the smallest value supported by both the by the Controller and use the smallest value supported by both the
Host and the Controller. Host and the Controller.
The Host supports sending of larger L2CAP PDUs than the ACL size and The Host supports sending of larger L2CAP PDUs than the ACL size and
will fragment L2CAP PDUs into ACL data packets. will fragment L2CAP PDUs into ACL data packets.
The Controller will return this value in the HCI LE Read Buffer The Controller will return this value in the HCI LE Read Buffer
@ -60,37 +61,21 @@ config BT_BUF_ACL_RX_SIZE
help help
Maximum support ACL size of data packets sent from the Controller to Maximum support ACL size of data packets sent from the Controller to
the Host. This value does not include the HCI ACL header. the Host. This value does not include the HCI ACL header.
In a combined Host and Controller build the buffer sizes in both the
Host and the Controller will use this value for buffer sizes, and In a combined Host and Controller build, both the
therefore Controller to Host flow Controller is not needed. Host and the Controller will use this value for buffer sizes, making
Controller to Host flow control not strictly necessary.
In a Host only build with Controller to Host flow control enabled In a Host only build with Controller to Host flow control enabled
the Host will inform the Controller about the maximum ACL data size it the Host will inform the Controller about the maximum ACL data size it
can send by setting this value in the Host Buffer Size command. can send by setting this value in the Host Buffer Size command.
If Controller to Host flow control is not enabled then the Controller If Controller to Host flow control is not enabled then the Controller
can assume the Host has infinite buffer size so this value should then can assume the Host has to receive and process ACL data faster than
be set to something that is guaranteed the Controller will not exceed the controller can produce it.
or the data packets will be dropped.
In a Controller only build this will determine the maximum ACL size In a Controller only build this will determine the maximum ACL size
that the Controller will send to the Host. that the Controller will send to the Host.
The Host supports reassembling of L2CAP PDUs from ACL data packets,
but the maximum supported L2CAP PDU size is limited by the maximum
supported ACL size.
This means the maximum L2CAP PDU MTU is restricted by the maximum ACL
size subtracting the 4 byte header of an L2CAP PDU.
When using L2CAP Connection oriented Channels without segmentation
then the L2CAP SDU MTU is also restricted by the maximum ACL size
subtracting the 4 Byte header of an L2CAP PDU plus the 2 byte header
of an L2CAP SDU.
With Enhanced ATT enabled the minimum of 70 is needed to support the
minimum ATT_MTU of 64 octets in an L2CAP SDU without segmentation.
With SMP LE Secure Connections enabled the minimum of 69 is needed to
support the minimum SMP MTU of 65 octets (public key + opcode) in an
L2CAP PDU.
An L2CAP PDU is also referred to as an L2CAP basic frame or B-frame.
An L2CAP SDU is also referred to as an L2CAP Credit-based frame or
K-frame.
config BT_BUF_ACL_RX_COUNT config BT_BUF_ACL_RX_COUNT
int "Number of incoming ACL data buffers" int "Number of incoming ACL data buffers"
@ -102,9 +87,11 @@ config BT_BUF_ACL_RX_COUNT
Host. Host.
In a combined Host and Controller build the buffers are shared and In a combined Host and Controller build the buffers are shared and
therefore Controller to Host flow control is not needed. therefore Controller to Host flow control is not needed.
In a Host only build with Controller to Host flow control enabled In a Host only build with Controller to Host flow control enabled
the Host will inform the Controller about the maximum number of the Host will inform the Controller about the maximum number of
buffers by setting this value in the Host Buffer Size command. buffers by setting this value in the Host Buffer Size command.
When Controller to Host flow control is not enabled the Controller When Controller to Host flow control is not enabled the Controller
can assume that the Host has infinite amount of buffers. can assume that the Host has infinite amount of buffers.