2021-04-08 08:12:47

by Marcel Holtmann

[permalink] [raw]
Subject: Re: [PATCH v2] Bluetooth: Add ncmd=0 recovery handling

Hi Manish,

> During command status or command complete event, the controller may set
> ncmd=0 indicating that it is not accepting any more commands. In such a
> case, host holds off sending any more commands to the controller. If the
> controller doesn't recover from such condition, host will wait forever,
> until the user decides that the Bluetooth is broken and may power cycles
> the Bluetooth.
>
> This patch triggers the hardware error to reset the controller and
> driver when it gets into such state as there is no other wat out.
>
> Reviewed-by: Abhishek Pandit-Subedi <[email protected]>
> Signed-off-by: Manish Mandlik <[email protected]>
> ---
>
> Changes in v2:
> - Emit the hardware error when ncmd=0 occurs
>
> include/net/bluetooth/hci.h | 1 +
> include/net/bluetooth/hci_core.h | 1 +
> net/bluetooth/hci_core.c | 15 +++++++++++++++
> net/bluetooth/hci_event.c | 10 ++++++++++
> 4 files changed, 27 insertions(+)
>
> diff --git a/include/net/bluetooth/hci.h b/include/net/bluetooth/hci.h
> index ea4ae551c426..c4b0650fb9ae 100644
> --- a/include/net/bluetooth/hci.h
> +++ b/include/net/bluetooth/hci.h
> @@ -339,6 +339,7 @@ enum {
> #define HCI_PAIRING_TIMEOUT msecs_to_jiffies(60000) /* 60 seconds */
> #define HCI_INIT_TIMEOUT msecs_to_jiffies(10000) /* 10 seconds */
> #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_POWER_OFF_TIMEOUT msecs_to_jiffies(5000) /* 5 seconds */
> diff --git a/include/net/bluetooth/hci_core.h b/include/net/bluetooth/hci_core.h
> index ebdd4afe30d2..f14692b39fd5 100644
> --- a/include/net/bluetooth/hci_core.h
> +++ b/include/net/bluetooth/hci_core.h
> @@ -470,6 +470,7 @@ struct hci_dev {
> struct delayed_work service_cache;
>
> struct delayed_work cmd_timer;
> + struct delayed_work ncmd_timer;
>
> struct work_struct rx_work;
> struct work_struct cmd_work;
> diff --git a/net/bluetooth/hci_core.c b/net/bluetooth/hci_core.c
> index b0d9c36acc03..c102a8763cb5 100644
> --- a/net/bluetooth/hci_core.c
> +++ b/net/bluetooth/hci_core.c
> @@ -2769,6 +2769,20 @@ static void hci_cmd_timeout(struct work_struct *work)
> queue_work(hdev->workqueue, &hdev->cmd_work);
> }
>
> +/* HCI ncmd timer function */
> +static void hci_ncmd_timeout(struct work_struct *work)
> +{
> + struct hci_dev *hdev = container_of(work, struct hci_dev,
> + ncmd_timer.work);
> +
> + bt_dev_err(hdev, "Controller not accepting commands anymore: ncmd = 0");
> +
> + /* This is an irrecoverable state. Inject hw error event to reset
> + * the device and driver.
> + */
> + hci_reset_dev(hdev);

/* This is an irrecoverable state, inject hardware error event */
hci_reset_dev(hdev);

Since you will not be resetting the driver here. You just tell the core stack to reset itself and with HCI_Reset hopefully bring the hardware back to life. Or if the ncmd=0 is a hardware bug, just start sending a new command.

> +}
> +
> struct oob_data *hci_find_remote_oob_data(struct hci_dev *hdev,
> bdaddr_t *bdaddr, u8 bdaddr_type)
> {
> @@ -3831,6 +3845,7 @@ struct hci_dev *hci_alloc_dev(void)
> init_waitqueue_head(&hdev->suspend_wait_q);
>
> INIT_DELAYED_WORK(&hdev->cmd_timer, hci_cmd_timeout);
> + INIT_DELAYED_WORK(&hdev->ncmd_timer, hci_ncmd_timeout);
>
> hci_request_setup(hdev);
>
> diff --git a/net/bluetooth/hci_event.c b/net/bluetooth/hci_event.c
> index cf2f4a0abdbd..114a9170d809 100644
> --- a/net/bluetooth/hci_event.c
> +++ b/net/bluetooth/hci_event.c
> @@ -3635,6 +3635,11 @@ static void hci_cmd_complete_evt(struct hci_dev *hdev, struct sk_buff *skb,
> if (*opcode != HCI_OP_NOP)
> cancel_delayed_work(&hdev->cmd_timer);
>
> + if (!ev->ncmd &&!test_bit(HCI_RESET, &hdev->flags))
> + schedule_delayed_work(&hdev->ncmd_timer, HCI_NCMD_TIMEOUT);
> + else
> + cancel_delayed_work(&hdev->ncmd_timer);
> +
> if (ev->ncmd && !test_bit(HCI_RESET, &hdev->flags))
> atomic_set(&hdev->cmd_cnt, 1);
>

if (!test_bit(HCI_RESET, &hdev->flags)) {
if (ev->ncmd) {
cancel_delayed_work(&hdev->ncmd_timer);
atomic_set(&hdev->cmd_cnt, 1);
} else {
schedule_delayed_work(&hdev->ncmd_timer,
HCI_NCMD_TIMEOUT);
}
}

I think doing it this way is a bit cleaner and avoid the check of !ncmd and !HCI_RESET twice.

And I wonder if there isn’t a cancel_delayed_work missing in hci_dev_do_close or some related location when we are shutting down.

What do we do when this happens during HCI_INIT. I think if ncmd_timer triggers during HCI_INIT, then hci_up needs to be aborted and no hardware error event to be injected.

In addition since you are now calling hci_reset_dev also from the core stack (perviously, it was just up to the drivers to do that), I would add an extra error.

diff --git a/net/bluetooth/hci_core.c b/net/bluetooth/hci_core.c
index fd12f1652bdf..1c9ef5608930 100644
--- a/net/bluetooth/hci_core.c
+++ b/net/bluetooth/hci_core.c
@@ -4073,6 +4073,8 @@ int hci_reset_dev(struct hci_dev *hdev)
hci_skb_pkt_type(skb) = HCI_EVENT_PKT;
skb_put_data(skb, hw_err, 3);

+ bt_dev_err(hdev, "Injecting HCI hardware error event");
+
/* Send Hardware Error to upper stack */
return hci_recv_frame(hdev, skb);
}

This has the advantage that if you take a btmon trace, you know this event is injected. Or more precisely eventually will be able to know since we haven’t merged my patches yet that will redirect bt_dev_{err,warn,..} into btmon as well.

Regards

Marcel