linux-kernel - Re: [PATCHv2] Bluetooth: quirk disabling LE Read Transmit Power

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Date:   Fri, 5 Nov 2021 14:47:39 -0700
From:   Luiz Augusto von Dentz <luiz.dentz@...il.com>
To:     Orlando Chamberlain <redecorating@...tonmail.com>
Cc:     Daniel Winkler <danielwinkler@...gle.com>,
        Johan Hedberg <johan.hedberg@...el.com>,
        "linux-bluetooth@...r.kernel.org" <linux-bluetooth@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Marcel Holtmann <marcel@...tmann.org>,
        regressions@...ts.linux.dev,
        Sonny Sasaka <sonnysasaka@...omium.org>
Subject: Re: [PATCHv2] Bluetooth: quirk disabling LE Read Transmit Power

Hi Orlando,

On Fri, Oct 1, 2021 at 1:56 AM Orlando Chamberlain
<redecorating@...tonmail.com> wrote:
>
> The LE Read Transmit Power command is Advertised on some Broadcom
> controlers, but not supported. Using this command breaks Bluetooth
> on the MacBookPro16,1 and iMac20,1. Added a quirk disabling LE Read
> Transmit Power for these devices, based off their common chip id 150.
>
> Link: https://lore.kernel.org/r/4970a940-211b-25d6-edab-21a815313954@protonmail.com
> Signed-off-by: Orlando Chamberlain <redecorating@...tonmail.com>
> ---
> v1->v2: Clarified quirk description
>
>  drivers/bluetooth/btbcm.c   |  4 ++++
>  include/net/bluetooth/hci.h | 11 +++++++++++
>  net/bluetooth/hci_core.c    |  3 ++-
>  3 files changed, 17 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/bluetooth/btbcm.c b/drivers/bluetooth/btbcm.c
> index e4182acee488..4ecc50d93107 100644
> --- a/drivers/bluetooth/btbcm.c
> +++ b/drivers/bluetooth/btbcm.c
> @@ -353,6 +353,10 @@ static int btbcm_read_info(struct hci_dev *hdev)
>                 return PTR_ERR(skb);
>
>         bt_dev_info(hdev, "BCM: chip id %u", skb->data[1]);
> +
> +       if (skb->data[1] == 150)
> +               set_bit(HCI_QUIRK_BROKEN_READ_TRANSMIT_POWER, &hdev->quirks);
> +
>         kfree_skb(skb);
>
>         /* Read Controller Features */
> diff --git a/include/net/bluetooth/hci.h b/include/net/bluetooth/hci.h
> index b80415011dcd..6da9bd6b7259 100644
> --- a/include/net/bluetooth/hci.h
> +++ b/include/net/bluetooth/hci.h
> @@ -246,6 +246,17 @@ enum {
>          * HCI after resume.
>          */
>         HCI_QUIRK_NO_SUSPEND_NOTIFIER,
> +
> +       /* When this quirk is set, LE Read Transmit Power is disabled.
> +        * This is mainly due to the fact that the HCI LE Read Transmit
> +        * Power command is advertised, but not supported; these
> +        * controllers often reply with unknown command and need a hard
> +        * reset.
> +        *
> +        * This quirk can be set before hci_register_dev is called or
> +        * during the hdev->setup vendor callback.
> +        */
> +       HCI_QUIRK_BROKEN_READ_TRANSMIT_POWER,
>  };
>
>  /* HCI device flags */
> diff --git a/net/bluetooth/hci_core.c b/net/bluetooth/hci_core.c
> index 8a47a3017d61..9a23fe7c8d67 100644
> --- a/net/bluetooth/hci_core.c
> +++ b/net/bluetooth/hci_core.c
> @@ -742,7 +742,8 @@ static int hci_init3_req(struct hci_request *req, unsigned long opt)
>                         hci_req_add(req, HCI_OP_LE_READ_ADV_TX_POWER, 0, NULL);
>                 }
>
> -               if (hdev->commands[38] & 0x80) {
> +               if (hdev->commands[38] & 0x80 &&
> +                       !test_bit(HCI_QUIRK_BROKEN_READ_TRANSMIT_POWER, &hdev->quirks)) {
>                         /* Read LE Min/Max Tx Power*/
>                         hci_req_add(req, HCI_OP_LE_READ_TRANSMIT_POWER,
>                                     0, NULL);
> --
> 2.33.0

Nowadays it is possible to treat errors such like this on a per
command basis (assuming it is not essential for the init sequence):

diff --git a/include/net/bluetooth/hci.h b/include/net/bluetooth/hci.h
index 979da5179ff4..f244f42cc609 100644
--- a/include/net/bluetooth/hci.h
+++ b/include/net/bluetooth/hci.h
@@ -551,6 +551,7 @@ enum {
 #define HCI_LK_AUTH_COMBINATION_P256   0x08

 /* ---- HCI Error Codes ---- */
+#define HCI_ERROR_UNKNOWN_CMD          0x01
 #define HCI_ERROR_UNKNOWN_CONN_ID      0x02
 #define HCI_ERROR_AUTH_FAILURE         0x05
 #define HCI_ERROR_PIN_OR_KEY_MISSING   0x06
diff --git a/net/bluetooth/hci_sync.c b/net/bluetooth/hci_sync.c
index bb88d31d2212..9c697e058974 100644
--- a/net/bluetooth/hci_sync.c
+++ b/net/bluetooth/hci_sync.c
@@ -3325,11 +3325,18 @@ static int
hci_le_read_adv_tx_power_sync(struct hci_dev *hdev)
 /* Read LE Min/Max Tx Power*/
 static int hci_le_read_tx_power_sync(struct hci_dev *hdev)
 {
+       int status;
+
        if (!(hdev->commands[38] & 0x80))
                return 0;

-       return __hci_cmd_sync_status(hdev, HCI_OP_LE_READ_TRANSMIT_POWER,
-                                    0, NULL, HCI_CMD_TIMEOUT);
+       status = __hci_cmd_sync_status(hdev, HCI_OP_LE_READ_TRANSMIT_POWER,
+                                      0, NULL, HCI_CMD_TIMEOUT);
+       /* Ignore if command is not really supported */
+       if (status == HCI_ERROR_UNKNOWN_CMD)
+               return 0;
+
+       return status;
 }

 /* Read LE Accept List Size */

Anyway, it would probably be worth pointing out to the vendor they
have a broken firmware if they do mark the command as supported but
return such error.

-- 
Luiz Augusto von Dentz