Re: [RFC] Bluetooth: Use non-flushable pb flag by default for ACL data on capable chipsets.

[Mat Martineau <mathewm@codeaurora.org>]

On Thu, 16 Dec 2010, Andrei Emeltchenko wrote:

> Hi,
>
> On Wed, Dec 15, 2010 at 6:35 PM, Mat Martineau <mathewm@codeaurora.org> wrote:
> <skipped>
>> There is one more thing missing:  Even though there is an L2CAP socket
>> option to set flush_to, and the flush_to is passed around during L2CAP
>> configuration, there is no use of the "Write Automatic Flush Timeout" HCI
>> command to tell the baseband what the flush timeout is!  Since the flush
>> timeout is shared across all connections on the ACL, how should BlueZ handle
>> the case where different flush timeouts are set on connections that share
>> the same ACL?  (My guess is that either the longest or shortest timeout
>> should be used, but there are good arguments either way)
>
> I would suggest bluetoothd to take care about setting Flush Timeout. 
> There is of course possibility to have sockopt for timeout and send 
> HCI command but this looks like a dirty hack.
>
> I think bluetoothd can read compare and write new flush timeout value.

There is *already* a sockopt for flush timeout (flush_to in 
l2cap_options, it was added before 2005), but it is not terribly 
useful because it does not configure the baseband.

One more piece of background information: The spec requires the 
default flush timeout to be infinite, so if no "Write Automatic Flush 
Timeout" command is sent, none of this flush code will accomplish 
anything.  Android has customized their version of BlueZ to send this 
command for A2DP connections, with certain BR/EDR basebands.

I don't have any major objection to managing this setting from 
bluetoothd.  My only minor objection is that it requires an 
application to manipulate the setting via DBus instead of using the 
existing sockopt - it would be confusing to have both available, but I 
suppose the sockopt could be deprecated or made read-only.  The flush 
timeout would seem to fit well as a device property.


--
Mat Martineau
Employee of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum