Bluetooth: Remove BT_HCI_RESERVE and BT_HCI_RAW_RESERVE

In most cases these were defined as 1. Saving one byte for the rest
doesn't really justify the added complexity that comes with these
options. Removing them also simplifies the interface between HCI
transports/drivers and the host stack, which in turn helps pave the way
for having HCI as a proper Zephyr driver API.

Fixes #71907

Signed-off-by: Johan Hedberg <johan.hedberg@gmail.com>

doc/releases/migration-guide-3.6.rst

@@ -476,6 +476,9 @@ Bluetooth
 * `BT_ISO_TIMESTAMP_NONE` has been removed and the `ts` parameter of :c:func:`bt_iso_chan_send` has
   as well. :c:func:`bt_iso_chan_send` now always sends without timestamp. To send with a timestamp,
   :c:func:`bt_iso_chan_send_ts` can be used.
+* The ``CONFIG_BT_HCI_RESERVE`` and ``CONFIG_BT_HCI_RAW_RESERVE`` Kconfig options were removed. All
+  buffers get by default one byte of headroom now, which HCI transport implementations can rely on
+  (whether they need it or not).
 
 Bluetooth Mesh
 ==============

include/zephyr/bluetooth/buf.h

@@ -51,11 +51,8 @@ struct bt_buf_data {
 	uint8_t type;
 };
 
-#if defined(CONFIG_BT_HCI_RAW)
+/* Headroom reserved in buffers, primarily for HCI transport encoding purposes */
-#define BT_BUF_RESERVE MAX(CONFIG_BT_HCI_RESERVE, CONFIG_BT_HCI_RAW_RESERVE)
+#define BT_BUF_RESERVE 1
-#else
-#define BT_BUF_RESERVE CONFIG_BT_HCI_RESERVE
-#endif
 
 /** Helper to include reserved HCI data in buffer calculations */
 #define BT_BUF_SIZE(size) (BT_BUF_RESERVE + (size))

samples/bluetooth/hci_ipc/nrf5340_cpunet_bis-bt_ll_sw_split.conf

@@ -10,7 +10,6 @@ CONFIG_HEAP_MEM_POOL_SIZE=8192
 
 CONFIG_BT=y
 CONFIG_BT_HCI_RAW=y
-CONFIG_BT_HCI_RAW_RESERVE=1
 CONFIG_BT_MAX_CONN=2
 
 # Workaround: Unable to allocate command buffer when using K_NO_WAIT since

samples/bluetooth/hci_ipc/nrf5340_cpunet_bt_mesh-bt_ll_sw_split.conf

@@ -8,7 +8,6 @@ CONFIG_SYSTEM_WORKQUEUE_STACK_SIZE=512
 
 CONFIG_BT=y
 CONFIG_BT_HCI_RAW=y
-CONFIG_BT_HCI_RAW_RESERVE=1
 CONFIG_BT_MAX_CONN=16
 
 

samples/bluetooth/hci_ipc/nrf5340_cpunet_cis-bt_ll_sw_split.conf

@@ -10,7 +10,6 @@ CONFIG_HEAP_MEM_POOL_SIZE=8192
 
 CONFIG_BT=y
 CONFIG_BT_HCI_RAW=y
-CONFIG_BT_HCI_RAW_RESERVE=1
 CONFIG_BT_MAX_CONN=2
 
 # Workaround: Unable to allocate command buffer when using K_NO_WAIT since

samples/bluetooth/hci_ipc/nrf5340_cpunet_df-bt_ll_sw_split.conf

@@ -10,7 +10,6 @@ CONFIG_HEAP_MEM_POOL_SIZE=8192
 
 CONFIG_BT=y
 CONFIG_BT_HCI_RAW=y
-CONFIG_BT_HCI_RAW_RESERVE=1
 CONFIG_BT_MAX_CONN=2
 
 # Workaround: Unable to allocate command buffer when using K_NO_WAIT since

samples/bluetooth/hci_ipc/nrf5340_cpunet_iso-bt_ll_sw_split.conf

@@ -11,7 +11,6 @@ CONFIG_CBPRINTF_REDUCED_INTEGRAL=y
 
 CONFIG_BT=y
 CONFIG_BT_HCI_RAW=y
-CONFIG_BT_HCI_RAW_RESERVE=1
 CONFIG_BT_MAX_CONN=2
 
 # Workaround: Unable to allocate command buffer when using K_NO_WAIT since

samples/bluetooth/hci_ipc/nrf5340_cpunet_iso_broadcast-bt_ll_sw_split.conf

@@ -10,7 +10,6 @@ CONFIG_HEAP_MEM_POOL_SIZE=8192
 
 CONFIG_BT=y
 CONFIG_BT_HCI_RAW=y
-CONFIG_BT_HCI_RAW_RESERVE=1
 
 # Workaround: Unable to allocate command buffer when using K_NO_WAIT since
 # Host number of completed commands does not follow normal flow control.

samples/bluetooth/hci_ipc/nrf5340_cpunet_iso_central-bt_ll_sw_split.conf

@@ -10,7 +10,6 @@ CONFIG_HEAP_MEM_POOL_SIZE=8192
 
 CONFIG_BT=y
 CONFIG_BT_HCI_RAW=y
-CONFIG_BT_HCI_RAW_RESERVE=1
 
 # Workaround: Unable to allocate command buffer when using K_NO_WAIT since
 # Host number of completed commands does not follow normal flow control.

samples/bluetooth/hci_ipc/nrf5340_cpunet_iso_peripheral-bt_ll_sw_split.conf

@@ -10,7 +10,6 @@ CONFIG_HEAP_MEM_POOL_SIZE=8192
 
 CONFIG_BT=y
 CONFIG_BT_HCI_RAW=y
-CONFIG_BT_HCI_RAW_RESERVE=1
 
 # Workaround: Unable to allocate command buffer when using K_NO_WAIT since
 # Host number of completed commands does not follow normal flow control.

samples/bluetooth/hci_ipc/nrf5340_cpunet_iso_receive-bt_ll_sw_split.conf

@@ -10,7 +10,6 @@ CONFIG_HEAP_MEM_POOL_SIZE=8192
 
 CONFIG_BT=y
 CONFIG_BT_HCI_RAW=y
-CONFIG_BT_HCI_RAW_RESERVE=1
 
 # Workaround: Unable to allocate command buffer when using K_NO_WAIT since
 # Host number of completed commands does not follow normal flow control.

samples/bluetooth/hci_ipc/prj.conf

@@ -8,7 +8,6 @@ CONFIG_SYSTEM_WORKQUEUE_STACK_SIZE=512
 
 CONFIG_BT=y
 CONFIG_BT_HCI_RAW=y
-CONFIG_BT_HCI_RAW_RESERVE=1
 CONFIG_BT_MAX_CONN=16
 
 

samples/bluetooth/hci_spi/prj.conf

@@ -6,7 +6,6 @@ CONFIG_BT=y
 CONFIG_BT_HCI_RAW=y
 CONFIG_BT_MAX_CONN=16
 CONFIG_BT_TINYCRYPT_ECC=n
-CONFIG_BT_HCI_RAW_RESERVE=1
 
 # Workaround: Unable to allocate command buffer when using K_NO_WAIT since
 # Host number of completed commands does not follow normal flow control.

subsys/bluetooth/Kconfig

@@ -61,15 +61,6 @@ config BT_HCI_RAW_H4_ENABLE
 	  This option enables use of H:4 transport for HCI RAW access at
 	  build time.
 
-config BT_HCI_RAW_RESERVE
-	int "Buffer headroom needed for HCI transport"
-	depends on BT_HCI_RAW
-	default 1 if BT_HCI_RAW_H4
-	default 0
-	help
-	  This option is used by the HCI raw transport implementation to
-	  declare how much headroom it needs for any HCI transport headers.
-
 config BT_HCI_RAW_CMD_EXT
 	bool "RAW HCI Command Extension"
 	help

subsys/bluetooth/host/Kconfig

@@ -72,27 +72,6 @@ config BT_HCI_TX_PRIO
 	int
 	default 7
 
-config BT_HCI_RESERVE
-	int
-	default 0 if BT_H4
-	default 1 if BT_H5
-	default 1 if BT_HCI_IPC
-	default 1 if BT_SPI
-	default 1 if BT_STM32_IPM
-	default 1 if BT_STM32WBA
-	default 1 if BT_USERCHAN
-	default 1 if BT_ESP32
-	default 0 if BT_B91
-	default 1 if BT_AMBIQ_HCI
-	default 1 if BT_SILABS_HCI
-	# Even if no driver is selected the following default is still
-	# needed e.g. for unit tests.
-	default 0
-	help
-	  Headroom that the driver needs for sending and receiving buffers. Add a
-	  new 'default' entry for each new driver.
-
-
 choice BT_RECV_CONTEXT
 	prompt "BT RX Thread Selection"
 	default BT_RECV_WORKQ_SYS if SOC_SERIES_NRF51X

tests/bsim/bluetooth/host/att/pipeline/tester/prj.conf

@@ -3,7 +3,6 @@ CONFIG_ASSERT=y
 
 CONFIG_BT=y
 CONFIG_BT_HCI_RAW=y
-CONFIG_BT_HCI_RAW_RESERVE=1
 CONFIG_BT_MAX_CONN=1
 
 CONFIG_BT_BUF_CMD_TX_COUNT=10

tests/bsim/bluetooth/host/att/sequential/tester/prj.conf

@@ -3,7 +3,6 @@ CONFIG_ASSERT=y
 
 CONFIG_BT=y
 CONFIG_BT_HCI_RAW=y
-CONFIG_BT_HCI_RAW_RESERVE=1
 CONFIG_BT_MAX_CONN=1
 
 CONFIG_BT_BUF_CMD_TX_COUNT=10

tests/bsim/bluetooth/host/l2cap/split/tester/prj.conf

@@ -3,7 +3,6 @@ CONFIG_ASSERT=y
 
 CONFIG_BT=y
 CONFIG_BT_HCI_RAW=y
-CONFIG_BT_HCI_RAW_RESERVE=1
 CONFIG_BT_MAX_CONN=16
 
 CONFIG_BT_BUF_CMD_TX_COUNT=10

tests/bsim/bluetooth/host/misc/disconnect/tester/prj.conf

@@ -3,7 +3,6 @@ CONFIG_ASSERT=y
 
 CONFIG_BT=y
 CONFIG_BT_HCI_RAW=y
-CONFIG_BT_HCI_RAW_RESERVE=1
 CONFIG_BT_MAX_CONN=1
 
 CONFIG_BT_BUF_CMD_TX_COUNT=10

tests/bsim/bluetooth/ll/cis/sysbuild/hci_ipc/nrf5340_cpunet_iso_acl_group-bt_ll_sw_split.conf

@@ -11,7 +11,6 @@ CONFIG_CBPRINTF_REDUCED_INTEGRAL=y
 
 CONFIG_BT=y
 CONFIG_BT_HCI_RAW=y
-CONFIG_BT_HCI_RAW_RESERVE=1
 CONFIG_BT_MAX_CONN=4
 
 # Workaround: Unable to allocate command buffer when using K_NO_WAIT since