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From: Arik Nemtsov <arik@wizery.com>
Date: Mon, 12 Mar 2012 20:07:08 +0200
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Subject: Re: [PATCH] mgmt-api: add read Tx power level command
To: Marcel Holtmann <marcel@holtmann.org>
Cc: linux-bluetooth@vger.kernel.org
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List-ID: <linux-bluetooth.vger.kernel.org>

On Mon, Mar 12, 2012 at 19:29, Marcel Holtmann <marcel@holtmann.org> wrote:
> Hi Arik,
>
>> >> This command reads the Tx power level for a given connected device
>> >> ---
>> >> =A0doc/mgmt-api.txt | =A0 28 ++++++++++++++++++++++++++++
>> >> =A01 files changed, 28 insertions(+), 0 deletions(-)
>> >>
>> >> diff --git a/doc/mgmt-api.txt b/doc/mgmt-api.txt
>> >> index 4ede43d..8dae2b4 100644
>> >> --- a/doc/mgmt-api.txt
>> >> +++ b/doc/mgmt-api.txt
>> >> @@ -815,6 +815,34 @@ Unblock Device Command
>> >> =A0 =A0 =A0 or failure.
>> >>
>> >>
>> >> +Read Tx Power Level Command
>> >> +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
>> >> +
>> >> + =A0 =A0 Command Code: =A0 =A0 =A0 =A0 =A0 0x0028
>> >
>> > how is this suppose to work. This command and Set Device ID are suppos=
e
>> > to have the same command code?
>>
>> Ah you're right I missed that. I'll put 0x29 then.
>>
>> >
>> >> + =A0 =A0 Controller Index: =A0 =A0 =A0 <controller id>
>> >> + =A0 =A0 Command Parameters: =A0 =A0 Address (6 Octets)
>> >> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 Address_Typ=
e (1 Octet)
>> >> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 Type (1 Oct=
et)
>> >> + =A0 =A0 Return Parameters: =A0 =A0 =A0Address (6 Octets)
>> >> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 Address_Typ=
e (1 Octet)
>> >> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 Status (1 O=
ctet)
>> >> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 Level (1 Oc=
tet)
>> >> +
>> >> + =A0 =A0 Possible values for the Address_Type parameter:
>> >> + =A0 =A0 =A0 =A0 =A0 =A0 0 =A0 =A0 =A0 BR/EDR
>> >> + =A0 =A0 =A0 =A0 =A0 =A0 1 =A0 =A0 =A0 LE Public
>> >> + =A0 =A0 =A0 =A0 =A0 =A0 2 =A0 =A0 =A0 LE Random
>> >> +
>> >> + =A0 =A0 Possible values for the Type parameter:
>> >> + =A0 =A0 =A0 =A0 =A0 =A0 0 =A0 =A0 =A0 Current Transmit Power Level
>> >> + =A0 =A0 =A0 =A0 =A0 =A0 1 =A0 =A0 =A0 Maximum Transmit Power Level
>> >
>> > Which ones do you care about? And why not just read both and return bo=
th
>> > at the same time.
>> >
>> > I think that I made this pretty clear multiple times already. The mgmt
>> > API is not for stuffing random HCI commands into it. Please explain yo=
ur
>> > usage pattern of the results clearly.
>> >
>> > Who is triggering this command and who is consuming the results?
>>
>> Well the proximity reporter and proximity monitor profiles are the
>> ones using this (with LE connections only). The proximity monitor can
>> query the reporter for the Tx power level. The spec claims there's no
>> point in polling for this, as the value doesn't change during an LE
>> connection.
>
> so why are we not just reading that value when creating a LE connection?
> What is the penalty for doing it on every LE connection?

Well presumably it should only be read when the TPS profile if
enabled. The cost is sending another command to the controller on each
connection. Not sure it's very high.
Maybe we can even integrate it into the "device connected" event, and
just read it for all connecting devices.

I guess it's a matter of personal preference.

I think this API is better for future proofing - it gives the caller
the option to get the Tx power for BR/EDR devices as well, at
arbitrary times (since it can change during a BR connection).
Some earlier emails suggested it might be useful.

>
>> Both profiles only care about the current Tx power level. I added the
>> type for flexibility. It can be removed of course.
>>
>> In the proposed implementation the reporter reads this value when a
>> device connects and caches it. When a remote device asks for this
>> value (via an ATT read as part of the TPS profile), we return the
>> cached value.
>
> So it gets always read anyway.

Only when TPS server is enabled.

Arik