linux-kernel - Re: [PATCH v2 0/4] Power off HCI devices before rfkilling them

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Date: Wed, 3 Jan 2024 13:15:52 +0100
From: Jonas Dreßler <verdre@...d.nl>
To: Luiz Augusto von Dentz <luiz.dentz@...il.com>
Cc: Marcel Holtmann <marcel@...tmann.org>,
 Johan Hedberg <johan.hedberg@...il.com>, asahi@...ts.linux.dev,
 linux-bluetooth@...r.kernel.org, linux-kernel@...r.kernel.org,
 netdev@...r.kernel.org, verdre@...d.nl
Subject: Re: [PATCH v2 0/4] Power off HCI devices before rfkilling them

Hi Luiz,

On 1/2/24 19:39, Luiz Augusto von Dentz wrote:
> Hi Jonas,
> 
> On Tue, Jan 2, 2024 at 1:19 PM Jonas Dreßler <verdre@...d.nl> wrote:
>>
>> In theory the firmware is supposed to power off the bluetooth card
>> when we use rfkill to block it. This doesn't work on a lot of laptops
>> though, leading to weird issues after turning off bluetooth, like the
>> connection timing out on the peripherals which were connected, and
>> bluetooth not connecting properly when the adapter is turned on again
>> quickly after rfkilling.
>>
>> This series hooks into the rfkill driver from the bluetooth subsystem
>> to send a HCI_POWER_OFF command to the adapter before actually submitting
>> the rfkill to the firmware and killing the HCI connection.
>>
>> ---
>>
>> v1 -> v2: Fixed commit message title to make CI happy
>>
>> Jonas Dreßler (4):
>>    Bluetooth: Remove HCI_POWER_OFF_TIMEOUT
>>    Bluetooth: mgmt: Remove leftover queuing of power_off work
>>    Bluetooth: Add new state HCI_POWERING_DOWN
>>    Bluetooth: Queue a HCI power-off command before rfkilling adapters
> 
> Apart from the assumption of RFKILL actually killing the RF
> immediately or not, I'm fine with these changes, that said it would be
> great if we can have some proper way to test the behavior of rfkill,
> perhaps via mgmt-tester, since it should behave like the
> MGMT_OP_SET_POWERED.

Testing this sounds like a good idea, I guess we'd have to teach 
mgmt-tester to write to rfkill. The bigger problem seems to be that 
there's no MGMT event for power changes and also no MGMT_OP_GET_POWERED, 
so that's a bit concerning, could userspace even be notified about 
changes to adapter power?

Another thing I'm thinking about now is that queuing the HCI command 
using hci_cmd_sync_queue() might not be enough: The command is still 
executed async in a thread, and we won't actually block until it has 
been sent, so this might be introducing a race (rfkill could kill the 
adapter before we actually send the HCI command). The proper way might 
be to use a completion and wait until the 
set_powered_off_sync_complete() callback is invoked?

> 
>>   include/net/bluetooth/hci.h |  2 +-
>>   net/bluetooth/hci_core.c    | 33 ++++++++++++++++++++++++++++++---
>>   net/bluetooth/hci_sync.c    | 16 +++++++++++-----
>>   net/bluetooth/mgmt.c        | 30 ++++++++++++++----------------
>>   4 files changed, 56 insertions(+), 25 deletions(-)
>>
>> --
>> 2.43.0
>>
> 
> 

Cheers,
Jonas