linux-kernel - Re: [PATCH v2] Bluetooth: btusb: Configure altsetting for USER

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Message-ID: <2025022407-polo-disgrace-9655@gregkh>
Date: Mon, 24 Feb 2025 07:44:34 +0100
From: Greg KH <gregkh@...uxfoundation.org>
To: Hsin-chen Chuang <chharry@...gle.com>
Cc: linux-bluetooth@...r.kernel.org, luiz.dentz@...il.com,
	chromeos-bluetooth-upstreaming@...omium.org,
	Hsin-chen Chuang <chharry@...omium.org>,
	Marcel Holtmann <marcel@...tmann.org>,
	Ying Hsu <yinghsu@...omium.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] Bluetooth: btusb: Configure altsetting for
 USER_CHANNEL

On Mon, Feb 24, 2025 at 02:25:52PM +0800, Hsin-chen Chuang wrote:
> Hi Greg,
> 
> On Mon, Feb 24, 2025 at 2:10 PM Greg KH <gregkh@...uxfoundation.org> wrote:
> >
> > On Mon, Feb 24, 2025 at 12:52:32PM +0800, Hsin-chen Chuang wrote:
> > > From: Hsin-chen Chuang <chharry@...omium.org>
> > >
> > > Automatically configure the altsetting for USER_CHANNEL when a SCO is
> > > connected. This adds support for the USER_CHANNEL to transfer SCO data
> > > over USB transport.
> > >
> > > Fixes: b16b327edb4d ("Bluetooth: btusb: add sysfs attribute to control USB alt setting")
> > > Signed-off-by: Hsin-chen Chuang <chharry@...omium.org>
> > > ---
> > >
> > > Changes in v2:
> > > - Give up tracking the SCO handles. Only configure the altsetting when
> > >   SCO connected.
> > > - Put the change behind Kconfig/module parameter
> > >
> > >  drivers/bluetooth/Kconfig | 11 ++++++++++
> > >  drivers/bluetooth/btusb.c | 46 +++++++++++++++++++++++++++++++++++++++
> > >  2 files changed, 57 insertions(+)
> > >
> > > diff --git a/drivers/bluetooth/Kconfig b/drivers/bluetooth/Kconfig
> > > index 4ab32abf0f48..7c497f878732 100644
> > > --- a/drivers/bluetooth/Kconfig
> > > +++ b/drivers/bluetooth/Kconfig
> > > @@ -56,6 +56,17 @@ config BT_HCIBTUSB_POLL_SYNC
> > >         Say Y here to enable USB poll_sync for Bluetooth USB devices by
> > >         default.
> > >
> > > +config BT_HCIBTUSB_AUTO_SET_ISOC_ALT
> > > +     bool "Auto set isoc_altsetting for USER_CHANNEL when SCO connected"
> > > +     depends on BT_HCIBTUSB
> > > +     default n
> > > +     help
> > > +       Say Y here to enable auto set isoc_altsetting for USER_CHANNEL
> > > +       when SCO connected
> > > +
> > > +       This can be overridden by passing btusb.auto_set_isoc_alt=[y|n]
> > > +       on the kernel commandline.
> > > +
> > >  config BT_HCIBTUSB_BCM
> > >       bool "Broadcom protocol support"
> > >       depends on BT_HCIBTUSB
> > > diff --git a/drivers/bluetooth/btusb.c b/drivers/bluetooth/btusb.c
> > > index de3fa725d210..af93d757911b 100644
> > > --- a/drivers/bluetooth/btusb.c
> > > +++ b/drivers/bluetooth/btusb.c
> > > @@ -34,6 +34,8 @@ static bool force_scofix;
> > >  static bool enable_autosuspend = IS_ENABLED(CONFIG_BT_HCIBTUSB_AUTOSUSPEND);
> > >  static bool enable_poll_sync = IS_ENABLED(CONFIG_BT_HCIBTUSB_POLL_SYNC);
> > >  static bool reset = true;
> > > +static bool auto_set_isoc_alt =
> > > +     IS_ENABLED(CONFIG_BT_HCIBTUSB_AUTO_SET_ISOC_ALT);
> > >
> > >  static struct usb_driver btusb_driver;
> > >
> > > @@ -1113,6 +1115,42 @@ static inline void btusb_free_frags(struct btusb_data *data)
> > >       spin_unlock_irqrestore(&data->rxlock, flags);
> > >  }
> > >
> > > +static void btusb_sco_connected(struct btusb_data *data, struct sk_buff *skb)
> > > +{
> > > +     struct hci_event_hdr *hdr = (void *) skb->data;
> > > +     struct hci_ev_sync_conn_complete *ev =
> > > +             (void *) skb->data + sizeof(*hdr);
> > > +     struct hci_dev *hdev = data->hdev;
> > > +     unsigned int notify_air_mode;
> > > +
> > > +     if (hci_skb_pkt_type(skb) != HCI_EVENT_PKT)
> > > +             return;
> > > +
> > > +     if (skb->len < sizeof(*hdr) || hdr->evt != HCI_EV_SYNC_CONN_COMPLETE)
> > > +             return;
> > > +
> > > +     if (skb->len != sizeof(*hdr) + sizeof(*ev) || ev->status)
> > > +             return;
> > > +
> > > +     switch (ev->air_mode) {
> > > +     case BT_CODEC_CVSD:
> > > +             notify_air_mode = HCI_NOTIFY_ENABLE_SCO_CVSD;
> > > +             break;
> > > +
> > > +     case BT_CODEC_TRANSPARENT:
> > > +             notify_air_mode = HCI_NOTIFY_ENABLE_SCO_TRANSP;
> > > +             break;
> > > +
> > > +     default:
> > > +             return;
> > > +     }
> > > +
> > > +     bt_dev_info(hdev, "enabling SCO with air mode %u", ev->air_mode);
> > > +     data->sco_num = 1;
> > > +     data->air_mode = notify_air_mode;
> > > +     schedule_work(&data->work);
> > > +}
> > > +
> > >  static int btusb_recv_event(struct btusb_data *data, struct sk_buff *skb)
> > >  {
> > >       if (data->intr_interval) {
> > > @@ -1120,6 +1158,11 @@ static int btusb_recv_event(struct btusb_data *data, struct sk_buff *skb)
> > >               schedule_delayed_work(&data->rx_work, 0);
> > >       }
> > >
> > > +     /* Configure altsetting for HCI_USER_CHANNEL on SCO connected */
> > > +     if (auto_set_isoc_alt &&
> > > +         hci_dev_test_flag(data->hdev, HCI_USER_CHANNEL))
> > > +             btusb_sco_connected(data, skb);
> > > +
> > >       return data->recv_event(data->hdev, skb);
> > >  }
> > >
> > > @@ -4354,6 +4397,9 @@ MODULE_PARM_DESC(enable_autosuspend, "Enable USB autosuspend by default");
> > >  module_param(reset, bool, 0644);
> > >  MODULE_PARM_DESC(reset, "Send HCI reset command on initialization");
> > >
> > > +module_param(auto_set_isoc_alt, bool, 0644);
> > > +MODULE_PARM_DESC(auto_set_isoc_alt, "Auto set isoc_altsetting for USER_CHANNEL when SCO connected");
> >
> > This is not the 1990's, why are you adding new module parameters when we
> > have so many other more proper ways to do this?  And really, this would
> 
> Sorry but could you please provide an example to guard a feature like this.

Depends on what you want to do with this configuration.  Why is it an
option at all?  Why can't it "just work"?  Module parameters are a pain
to configure, we have loads of other ways to do this now (configfs,
debugfs for debugging stuff, sysfs for device-specific things, etc.)

> > not work at all for multiple controllers in teh same system, right?
> 
> Do you mean we can't have separate parameters for different
> controllers? Yes that's true, but why would a user want the different
> behavior on the same machine?

Why would you prevent them from allowing this to happen for a
device-specific option?

thanks,

greg k-h