Return-Path: MIME-Version: 1.0 In-Reply-To: References: <35c90d960911121639o8b0b0bfxde880af69adc9f95@mail.gmail.com> <1258082098.7715.7.camel@violet> <35c90d960911121931n687a2cd4ie8130f919041ee70@mail.gmail.com> <1258084357.7715.26.camel@violet> <35c90d960911131445w16076c70sa0473e9b459d7d15@mail.gmail.com> <35c90d961001122046o733c7e10nf28bfed9e7f5465@mail.gmail.com> <1263366291.922.5.camel@localhost.localdomain> Date: Tue, 3 Aug 2010 17:32:46 +0800 Message-ID: Subject: Re: What is the motivation for conn->power_save From: Liang Bao To: Nick Pelly Cc: Andrei Emeltchenko , Marcel Holtmann , linux-bluetooth@vger.kernel.org Content-Type: text/plain; charset=ISO-8859-1 List-ID: Hi, 2010/7/9 Nick Pelly > > On Thu, Jul 8, 2010 at 8:07 AM, Andrei Emeltchenko > wrote: > > Hi, > > > > On Wed, Jan 13, 2010 at 10:04 AM, Marcel Holtmann = 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 dat= a to > >>> >>> >> send, then it seems like a good idea for the host stack to exp= licitly > >>> >>> >> 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 mode= s. But > >>> >>> >> the conn->power_save code is getting in the way and doesn't ap= pear 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 fall= s flat on > >>> >>> > its face. They need to stay in control of sniff mode if they in= itiated > >>> >>> > 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 thi= s 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 t= hen it is > >>> >>> > clearly not an HID device. However even A2DP has this sort of p= roblems > >>> >>> > sometimes where the stream setup takes time. > >>> >>> > >>> >>> Makes sense. Thanks for the explanation. > >>> >> > >>> >> this means you will be working on a patch for this :) > >>> > >>> Actually, I want to put a patch together for a socket option to not > >>> use power_save (so that we *always* exit sniff mode when sending ACL > >>> data). We're seeing this problem with the Plantronics Voyager 855 > >>> which enters sniff mode during A2DP. > >>> > >>> Given that power_save is just for HID devices, my preferred design is > >>> to disable power_save by default, and have an L2CAP socket option to > >>> turn on power_save that would be used by HID L2CAP sockets. > >>> Unfortunately this would require userspace HID code to use the new > >>> socket option to keep current behavior. But it seems preferable to th= e > >>> alternative of having every single other L2CAP socket use a new socke= t > >>> option just to disable power_save for the sake of HID. > >> > >> actually you still mix up the meaning of the power_save option. From t= he > >> stack side, the automatic sniff mode is off by default. You have to > >> enable via sysfs first. The power_save option is just to control when > >> sniff mode is activated and the remote enters sniff mode, that we are > >> not getting out of it if we have ACL data. > >> > >> In conclusion, I am fine with a socket option that allows to control > >> sniff mode (preferable with interval details) and sniff subrate detail= s > >> so that we can use them for that ACL link. > >> > >> So go ahead and work on this. We can fix userspace easily since a new > >> socket can be detected easily with newer kernels. > > > > We have found that some Nokia BT headsets stop working after idle > > period when they enter > > "power save" mode. > > > > Do we have any solution for this problem? So far I see good enough > > patch :-)) below: > > > > http://android.git.kernel.org/?p=3Dkernel/common.git;a=3Dblobdiff;f=3Dn= et/bluetooth/hci_conn.c;h=3Dfa8b412205cd89546b4a325c558c68040eeaf491;hp=3D0= cf25114a3f576fc2788a549eb96d0087dd39b44;hb=3Dd8488237646920cd71ef43e5f3ae10= 01c6f4cf7b;hpb=3D3f68e5050c5ae559f56d5da9202cb88928d42b36 > > > > - =A0 =A0 =A0 if (conn->mode !=3D HCI_CM_SNIFF || !conn->power_save) > > + =A0 =A0 =A0 if (conn->mode !=3D HCI_CM_SNIFF /* || !conn->power_save = */) > > > > Nick have you done socket option for "power_save"? > > No. We'll do it once we need it for HID support. Can we do this: try to do check against some existing fields in structure hci_conn, for example device_class and then determine if conn->power_save shall be used here? By doing this, applications in user space can be saved from having knowledge how sniff mode works for different devices. Alternatively, is it possible to add another flag - I know the structure is getting big so I agree adding something might not be a good idea. :) > > Nick > -- > To unsubscribe from this list: send the line "unsubscribe linux-bluetooth= " in > the body of a message to majordomo@vger.kernel.org > More majordomo info at =A0http://vger.kernel.org/majordomo-info.html