netdev - Re: [PATCH] Bluetooth: silence a dmesg error message in hci

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Date:   Thu, 17 Nov 2022 20:34:16 +0000
From:   "Gix, Brian" <brian.gix@...el.com>
To:     "mat.jonczyk@...pl" <mat.jonczyk@...pl>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-bluetooth@...r.kernel.org" <linux-bluetooth@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     "Von Dentz, Luiz" <luiz.von.dentz@...el.com>,
        "johan.hedberg@...il.com" <johan.hedberg@...il.com>,
        "marcel@...tmann.org" <marcel@...tmann.org>
Subject: Re: [PATCH] Bluetooth: silence a dmesg error message in hci_request.c

Hi Mateusz,

On Wed, 2022-11-16 at 21:28 +0100, Mateusz Jończyk wrote:
> On kernel 6.1-rcX, I have been getting the following dmesg error
> message
> on every boot, resume from suspend and rfkill unblock of the
> Bluetooth
> device:
> 
>         Bluetooth: hci0: HCI_REQ-0xfcf0
> 

This has a patch that fixes the usage of the deprecated HCI_REQ
mechanism rather than hiding the fact it is being called, as in this
case.

I am still waiting for someone to give me a "Tested-By:" tag to patch:

[PATCH 1/1] Bluetooth: Convert MSFT filter HCI cmd to hci_sync

Which will also stop the dmesg error. If you could try that patch, and
resend it to the list with a Tested-By tag, it can be applied.

We still want to be allerted to deprecated usage situations.

> After some investigation, it turned out to be caused by
> commit dd50a864ffae ("Bluetooth: Delete unreferenced hci_request
> code")
> which modified hci_req_add() in net/bluetooth/hci_request.c to always
> print an error message when it is executed. In my case, the function
> was
> executed by msft_set_filter_enable() in net/bluetooth/msft.c, which
> provides support for Microsoft vendor opcodes.
> 
> As explained by Brian Gix, "the error gets logged because it is using
> a
> deprecated (but still working) mechanism to issue HCI opcodes" [1].
> So
> this is just a debugging tool to show that a deprecated function is
> executed. As such, it should not be included in the mainline kernel.
> See for example
> commit 771c035372a0 ("deprecate the '__deprecated' attribute warnings
> entirely and for good")
> Additionally, this error message is cryptic and the user is not able
> to
> do anything about it.
> 
> [1]
> Link:
> https://lore.kernel.org/lkml/beb8dcdc3aee4c5c833aa382f35995f17e7961a1.camel@intel.com/
> 
> Fixes: dd50a864ffae ("Bluetooth: Delete unreferenced hci_request
> code")
> Signed-off-by: Mateusz Jończyk <mat.jonczyk@...pl>
> Cc: Brian Gix <brian.gix@...el.com>
> Cc: Luiz Augusto von Dentz <luiz.von.dentz@...el.com>
> Cc: Marcel Holtmann <marcel@...tmann.org>
> Cc: Johan Hedberg <johan.hedberg@...il.com>
> ---
>  net/bluetooth/hci_request.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/bluetooth/hci_request.c
> b/net/bluetooth/hci_request.c
> index 5a0296a4352e..f7e006a36382 100644
> --- a/net/bluetooth/hci_request.c
> +++ b/net/bluetooth/hci_request.c
> @@ -269,7 +269,7 @@ void hci_req_add_ev(struct hci_request *req, u16
> opcode, u32 plen,
>  void hci_req_add(struct hci_request *req, u16 opcode, u32 plen,
>                  const void *param)
>  {
> -       bt_dev_err(req->hdev, "HCI_REQ-0x%4.4x", opcode);
> +       bt_dev_dbg(req->hdev, "HCI_REQ-0x%4.4x", opcode);
>         hci_req_add_ev(req, opcode, plen, param, 0);
>  }
>  
> 
> base-commit: 094226ad94f471a9f19e8f8e7140a09c2625abaa

Regards,
--Brian Gix