Hi Marcel, On Thu, Nov 12, 2009 at 7:14 PM, Marcel Holtmann <marcel@xxxxxxxxxxxx> wrote: > Hi Nick, > >> If I understand correctly, conn->power_save prevents the host stack >> from requesting active mode if it was not the host stack that >> requested sniff mode. >> >> I don't understand the motivation for this. If we have ACL data to >> send, then it seems like a good idea for the host stack to explicitly >> request active mode, regardless of the reason that we entered sniff >> mode. >> >> We want to enter active mode more aggressively when setting up SCO >> connections, to avoid a 5 second delay with certain sniff modes. But >> the conn->power_save code is getting in the way and doesn't appear to >> be useful in the first place. > > we have discussed this a few times. And if you lock through the code > history then you see that initially we just took devices out of sniff > mode if we had to send data. However with HID devices this falls flat on > its face. They need to stay in control of sniff mode if they initiated > it. Some of them crash and others just drain the battery. With sniff > mode you can send small amounts of data even while in sniff and for HID > that is sometimes used. So the remote side better not interfere. > > What we really need is a socket option where we can control this on a > per socket basis if we take devices out of sniff mode. And one extra > case might be when we try to establish a SCO channel, because then it is > clearly not an HID device. However even A2DP has this sort of problems > sometimes where the stream setup takes time. Makes sense. Thanks for the explanation. > Not sure if we have to make SCO setup special. The only reason would be > if there is a case where we don't get an AT command before SCO needs to > be established. If you are in-call, and transfer audio from handset to BT headset, then there is SCO setup without any AT command. I think for the SCO setup case we would always want to enter active mode. I could modify enter_active_mode() to take a parameter like 'int force' that would force us to enter active mode regardless of the state of power_save, and use this when setting up SCO. What do you think? Nick -- To unsubscribe from this list: send the line "unsubscribe linux-bluetooth" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
