[PATCH v1] Bluetooth: Increase HCI_AUTO_OFF_TIMEOUT to 10 seconds

[Shuai Zhang]

HCI_AUTO_OFF_TIMEOUT controls how long the kernel waits after an
adapter completes its initial setup before automatically powering
it off, in case userspace (bluetoothd) has not yet issued
MGMT_OP_SET_POWERED. This avoids leaving the controller powered
while unused.

On platforms where other services are ordered ahead of it, the
actual time at which bluetooth.service starts and issues
SET_POWERED can be delayed past this 2 second window. For example,
cloud-init-local.service can perform a network metadata probe
during early boot, delaying bluetooth.service startup by several
seconds:

    $ systemd-analyze critical-chain bluetooth.service
    bluetooth.service +594ms
     `-basic.target @9.342s
        `-sockets.target @9.335s
           `-snapd.socket @9.267s +58ms
              `-sysinit.target @9.025s
                 `-cloud-init.service @8.377s +604ms
                    `-cloud-init-local.service @7.000s +1.340s
                       `-systemd-remount-fs.service @3.257s +44ms
                          `-systemd-fsck-root.service @2.803s +394ms
                             `-systemd-journald.socket @2.223s
                                `-system.slice @1.772s
                                   `--.slice @1.772s

Once the 2 second window is exceeded, HCI_AUTO_OFF fires before
SET_POWERED is received, powering off the controller and losing
its firmware state. The SET_POWERED that bluetoothd eventually
sends then has to reopen the device, triggering an otherwise
avoidable repeat setup and firmware re-download, adding several
more seconds of delay.

Increase the timeout from 2 to 10 seconds to give userspace on
systems with slower service ordering a more realistic window to
take over, avoiding this unnecessary repeat setup, while still
bounding how long an unclaimed controller stays powered on.

Signed-off-by: Shuai Zhang <shuai.zhang@xxxxxxxxxxxxxxxx>
---
 include/net/bluetooth/hci.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/net/bluetooth/hci.h b/include/net/bluetooth/hci.h
index 50f0eef71..ee3f295f9 100644
--- a/include/net/bluetooth/hci.h
+++ b/include/net/bluetooth/hci.h
@@ -483,7 +483,7 @@ enum {
 #define HCI_CMD_TIMEOUT		msecs_to_jiffies(2000)	/* 2 seconds */
 #define HCI_NCMD_TIMEOUT	msecs_to_jiffies(4000)	/* 4 seconds */
 #define HCI_ACL_TX_TIMEOUT	msecs_to_jiffies(45000)	/* 45 seconds */
-#define HCI_AUTO_OFF_TIMEOUT	msecs_to_jiffies(2000)	/* 2 seconds */
+#define HCI_AUTO_OFF_TIMEOUT	msecs_to_jiffies(10000)	/* 10 seconds */
 #define HCI_ACL_CONN_TIMEOUT	msecs_to_jiffies(20000)	/* 20 seconds */
 #define HCI_LE_CONN_TIMEOUT	msecs_to_jiffies(20000)	/* 20 seconds */
 #define HCI_ISO_TX_TIMEOUT	usecs_to_jiffies(0x7fffff) /* 8388607 usecs */
-- 
2.34.1