Message-ID: <CABBYNZL26agc8mDaWZhSpWO1uzhZ78QY96n3OEQW3GJw9+UPYQ@mail.gmail.com>
Date: Sun, 7 Jan 2024 18:49:15 -0500
From: Luiz Augusto von Dentz <luiz.dentz@...il.com>
To: Jonas Dreßler <verdre@...d.nl>
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
Subject: Re: [PATCH v2 0/4] Power off HCI devices before rfkilling them

Hi Jonas,

On Sun, Jan 7, 2024 at 1:11 PM Jonas Dreßler <verdre@...d.nl> wrote:
>
> On 1/3/24 13:15, Jonas Dreßler wrote:
> > 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?
>
> Sent v3 of the patchset now, I didn't add a test to mgmt-tester because
> it's actually quite tricky to notice the full shutdown sequence happened
> rather than just closing the device. As long as no devices are
> connected, the difference is mostly in a few (faily random) events:
>
> btmon without the patch:
>
> @ MGMT Event: Class Of Device Changed (0x0007) plen 3
>
>         {0x0001} [hci0] 169.101804
>          Class: 0x000000
>            Major class: Miscellaneous
>            Minor class: 0x00
> @ MGMT Event: New Settings (0x0006) plen 4
>
>         {0x0001} [hci0] 169.101820
>          Current settings: 0x00000ac0
>            Secure Simple Pairing
>            BR/EDR
>            Low Energy
>            Secure Connections
>
> btmon with the patch:
>
> < HCI Command: Write Scan Enable (0x03|0x001a) plen 1
>
>               #109 [hci0] 7.031852
>          Scan enable: No Scans (0x00)
>  > HCI Event: Command Complete (0x0e) plen 4
>
>                #110 [hci0] 7.033026
>        Write Scan Enable (0x03|0x001a) ncmd 1
>          Status: Success (0x00)
> < HCI Command: LE Set Extended Advertising Enable (0x08|0x0039) plen 2
>
>               #111 [hci0] 7.033055
>          Extended advertising: Disabled (0x00)
>          Number of sets: Disable all sets (0x00)
>  > HCI Event: Command Complete (0x0e) plen 4
>
>                #112 [hci0] 7.034202
>        LE Set Extended Advertising Enable (0x08|0x0039) ncmd 1
>          Status: Success (0x00)
> < HCI Command: LE Clear Advertising Sets (0x08|0x003d) plen 0
>
>               #113 [hci0] 7.034233
>  > HCI Event: Command Complete (0x0e) plen 4
>
>                #114 [hci0] 7.035527
>        LE Clear Advertising Sets (0x08|0x003d) ncmd 1
>          Status: Success (0x00)
> @ MGMT Event: Class Of Device Changed (0x0007) plen 3
>
>           {0x0001} [hci0] 7.035554
>          Class: 0x000000
>            Major class: Miscellaneous
>            Minor class: 0x00
> @ MGMT Event: New Settings (0x0006) plen 4
>
>           {0x0001} [hci0] 7.035568
>          Current settings: 0x00000ac0
>            Secure Simple Pairing
>            BR/EDR
>            Low Energy
>            Secure Connections
>
> Maybe we could add a fake connection and check whether that is
> disconnected on the rfkill, but I don't think mgmt-tester supports that..
>
> Fwiw, I don't think having a test for this is super important, this is a
> regression a lot of people would notice very quickly I think.

Afaik we did something similar to suspend to test its sequence when
suspending while connected, I will look it up tomorrow since I
responding from my phone.

> >
> > 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
>
> Cheers,
> Jonas



-- 
Luiz Augusto von Dentz

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