Hi,
I am using hciattach to bind tty to bluetooth HCI.
There is an error printout:
Code:
Bluetooth: hci0: sending frame failed (-49)
After some investigation, I found the kernel may miss some sync in bluetooth codes.
1. hciattach command calls ioctl(HCIUARTSETPROTO) to set prototype, it goes down to kernel through syscall, calls hci_uart_tty_ioctl, then hci_uart_set_proto, then hci_uart_register_dev and finally set HCI_UART_PROTO_READY.
2. For hci_uart_register_dev which I mentioned in the 1st step, it calls hci_register_dev, and starts a workqueue hdev->power_on.
3. For hdev->power_on workqueue, it in further callls hci_dev_do_open, then hci_uart_setup, then set_baudrate, then __hci_cmd_sync which starts another workqueue hdev->cmd_work.
4. For hdev->cmd_work workqueue, it calls hci_send_frame, then hci_uart_send_frame, which will test HCI_PROTO_READ bit, if it is not set, then return -EUNATCH, which is -49.
So for all these complicated calls and workqueues, the workqueue which is triggered by hci_uart_register_dev, may be executed before HCI_UART_PROTO_READY which is set in hci_uart_set_proto right after hci_uart_register_dev, that leads to -49 error.
After adding a piece of code before __hci_cmd_sync in send_baudrate, it works alright
Code:
do {
if (test_bit(HCI_UART_PROTO_READY, &hu->flags)) {
return 0;
}
udelay(100);
} while (time_before(jiffies, timeout));
I am working on kernel version v5.4, but I checked the latest kernel v6.6.7, seems it is the same.
Has anyone met a similar issue before? Is it the kernel bluetooth that lacks sync in this case?
Any help will be appreciated! Thank you!
BR,
Peng
Kernel miss sync when binding bluetooth HCI interface?
