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

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Message-ID: <53897886.3020200@ahsoftware.de>
Date:	Sat, 31 May 2014 08:36:54 +0200
From:	Alexander Holler <holler@...oftware.de>
To:	Marcel Holtmann <marcel@...tmann.org>
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

Am 31.05.2014 07:32, schrieb Marcel Holtmann:
> 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.

As I said in another mail, I don't think it is the chip. On the system
where I'm experiencing these timeouts there's still the USB-subsysten
inbetween. And this system boots from USB too, which means there's a lot
of other traffic on the USB-bus besides the one for the USB-BT-dongle.
And I don't know how the USB-stack (and hw) schedules the traffic, if he
is able to schedule that at all.

Regards,

Alexander
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