linux-kernel - Re: [PATCH 2/2] bluetooth: raise HCI_CMD

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Message-Id: <B76D7881-8AE8-480D-A53B-B300DDEEBC47@holtmann.org>
Date:	Sat, 31 May 2014 07:32:31 +0200
From:	Marcel Holtmann <marcel@...tmann.org>
To:	Alexander Holler <holler@...oftware.de>
Cc:	linux-kernel@...r.kernel.org, linux-bluetooth@...r.kernel.org,
	"Gustavo F. Padovan" <gustavo@...ovan.org>,
	Johan Hedberg <johan.hedberg@...il.com>
Subject: Re: [PATCH 2/2] bluetooth: raise HCI_CMD_TIMEOUT from 2s to 8s

Hi Alexander,

> The reasoning to do this is the following:
> 
> - If a timeout occurs, the HCI-communication is broken afterwards and the
>  dongle isn't usable anymore.
> - If it works after e.g. waiting 4s everyone is still happy but if it
>  just breaks after only waiting 2s nothing is gained.
> - Having to wait some more seconds until an error occurs doesn't change
>  anything.
> 
> So there is no disadvantage in rasing the timeout but a great advantage
> in case the dongle needs more than 2s to process an HCI command.
> E.g. I had sometimes HCI command timeouts at boot (but never after the BT stack
> was successfull started). I assume the reason might be the USB-probing which
> happend before through the bootloader, which might have confused the dongle
> such that it needs a bit more time, but I'm not sure.
> 
> Together with the patch which limits the timeout only to the actual time the
> dongle needs to process an HCI command (and doesn't include the time the
> kernel needs to process the answer to an HCI command), my problems were gone.
> 
> Signed-off-by: Alexander Holler <holler@...oftware.de>
> ---
> 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 be150cf..d50fd34 100644
> --- a/include/net/bluetooth/hci.h
> +++ b/include/net/bluetooth/hci.h
> @@ -180,7 +180,7 @@ enum {
> #define HCI_DISCONN_TIMEOUT	msecs_to_jiffies(2000)	/* 2 seconds */
> #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_CMD_TIMEOUT		msecs_to_jiffies(8000)	/* 8 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 */

I think moving the command timeout handling into a delayed work struct might actually solve this problem nicely and does not force us to increase the timeout. A chip that does not respond for 8 seconds is a pretty bad chip.

Regards

Marcel

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