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bluetooth: classic: GOEP: fix L2CAP MTU calculation

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Correct the minimum MTU calculation for GOEP over L2CAP to account
for the L2CAP I-frame overhead.

- Update BT_BUF_ACL_RX_SIZE default from 264 to 265 bytes for GOEP
- Update BT_GOEP_L2CAP_MTU minimum range from 259 to 265 bytes
- Add detailed comment explaining L2CAP I-frame field length (6 bytes):
  * 4 bytes for extended control field
  * 2 bytes for FCS field

The previous calculation only accounted for the L2CAP header (4 bytes)
but missed the 6-byte L2CAP I-frame overhead (extended control field
and FCS), resulting in an incorrect minimum of 264 bytes instead
of the correct 265 bytes. And it causes the minimum MTU of L2CAP
to be incorrectly set to 254. The MTU cannot meet the minimum
requirement of GOEP MOPL.

The correct calculation for GOEP over L2CAP is:
255 bytes (GOEP minimum MTU) + 4 bytes (L2CAP header) + 6 bytes
(L2CAP I-frame) = 265 bytes total.

Set the default value of CONFIG_BT_BUF_ACL_RX_SIZE to 265 if GOEP is
enabled.

Signed-off-by: Lyle Zhu <lyle.zhu@nxp.com>
This commit is contained in:
Lyle Zhu
2025-12-31 11:51:36 +08:00
committed by Henrik Brix Andersen
parent 2247f4dc7a
commit cc18a23ec9
2 changed files with 12 additions and 3 deletions
Download Patch File Download Diff File Expand all files Collapse all files

10
subsys/bluetooth/common/Kconfig
View File

@@ -50,11 +50,17 @@ config BT_BUF_ACL_TX_COUNT
config BT_BUF_ACL_RX_SIZE
int "Maximum supported ACL size for incoming data"
# For GOEP over RFCOMM, including,
# For GOEP over RFCOMM, the minimum MTU of GOEP is 264, including,
# 255 bytes - the minimum MTU of GOEP,
# 4 bytes - L2CAP Header,
# 5 bytes - 4 bytes for RFCOMM header with extended length, 1 byte for FCS.
default 264 if BT_CLASSIC && BT_GOEP
# For GOEP over L2CAP, the minimum MTU of GOEP is 265, including,
# 255 bytes - the minimum MTU of GOEP,
# 4 bytes - L2CAP Header,
# 6 bytes - Field length of L2CAP I-frame, including,
# 4 bytes - extended control field,
# 2 bytes - FCS field.
default 265 if BT_CLASSIC && BT_GOEP
default 200 if BT_CLASSIC
default 70 if BT_EATT
default 69 if BT_SMP

5
subsys/bluetooth/host/classic/Kconfig
View File

@@ -685,7 +685,10 @@ config BT_GOEP_L2CAP_MTU
# For GOEP over L2CAP, including,
# 255 bytes - the minimum MTU of GOEP,
# 4 bytes - L2CAP Header,
range 259 BT_BUF_ACL_RX_SIZE
# 6 bytes - Field length of L2CAP I-frame, including,
# 4 bytes - extended control field,
# 2 bytes - FCS field.
range 265 BT_BUF_ACL_RX_SIZE
help
Maximum size of L2CAP MTU for GOEP.
RX MTU will be truncated to account for ACL data and type overhead, and the L2CAP PDU