Re: [PATCH] Bluetooth: btusb: Lower passive lescan interval on Marvell 88W8897

[Jonas Dreßler]

On 9/17/21 2:35 PM, Marcel Holtmann wrote:
> Hi Jonas,
>
> > The Marvell 88W8897 combined wifi and bluetooth card (pcie+usb version)
> > is used in a lot of Microsoft Surface devices, and all those devices
> > suffer from very low 2.4GHz wifi connection speeds while bluetooth is
> > enabled. The reason for that is that the default passive scanning
> > interval for Bluetooth Low Energy devices is quite high on Linux
> > (interval of 60 msec and scan window of 30 msec, see le_scan_interval
> > and le_scan_window in hci_core.c), and the Marvell chip is known for its
> > bad bt+wifi coexisting performance.
> >
> > So decrease that passive scan interval and make the scan window shorter
> > on this particular device to allow for spending more time transmitting
> > wifi signals: The new scan interval is 250 msec (0x190 * 0.625 msec) and
> > the new scan window is 6.25 msec (0xa * 0.625 msec).
> >
> > This change has a very large impact on the 2.4GHz wifi speeds and gets
> > it up to performance comparable with the Windows driver, which seems to
> > apply a similar quirk.
> >
> > The scan interval and scan window length were tested and found to work
> > very well with a bunch of Bluetooth Low Energy devices, including the
> > Surface Pen, a Bluetooth Speaker and two modern Bluetooth headphones.
> > All devices were discovered immediately after turning them on. Even
> > lower values were also tested, but these introduced longer delays until
> > devices get discovered.
> >
> > Signed-off-by: Jonas Dreßler <verdre@xxxxxxx>
> > ---
> > drivers/bluetooth/btusb.c | 15 +++++++++++++++
> > 1 file changed, 15 insertions(+)
> >
> > diff --git a/drivers/bluetooth/btusb.c b/drivers/bluetooth/btusb.c
> > index 60d2fce59a71..05b11179c839 100644
> > --- a/drivers/bluetooth/btusb.c
> > +++ b/drivers/bluetooth/btusb.c
> > @@ -59,6 +59,7 @@ static struct usb_driver btusb_driver;
> > #define BTUSB_WIDEBAND_SPEECH	0x400000
> > #define BTUSB_VALID_LE_STATES   0x800000
> > #define BTUSB_QCA_WCN6855	0x1000000
> > +#define BTUSB_LOWER_LESCAN_INTERVAL	0x2000000
> > #define BTUSB_INTEL_BROKEN_INITIAL_NCMD 0x4000000
> >
> > static const struct usb_device_id btusb_table[] = {
> > @@ -356,6 +357,7 @@ static const struct usb_device_id blacklist_table[] = {
> > 	{ USB_DEVICE(0x1286, 0x2044), .driver_info = BTUSB_MARVELL },
> > 	{ USB_DEVICE(0x1286, 0x2046), .driver_info = BTUSB_MARVELL },
> > 	{ USB_DEVICE(0x1286, 0x204e), .driver_info = BTUSB_MARVELL },
> > +	{ USB_DEVICE(0x1286, 0x204c), .driver_info = BTUSB_LOWER_LESCAN_INTERVAL },
> >
> > 	/* Intel Bluetooth devices */
> > 	{ USB_DEVICE(0x8087, 0x0025), .driver_info = BTUSB_INTEL_COMBINED },
> > @@ -3813,6 +3815,19 @@ static int btusb_probe(struct usb_interface *intf,
> > 	if (id->driver_info & BTUSB_MARVELL)
> > 		hdev->set_bdaddr = btusb_set_bdaddr_marvell;
> >
> > +	/* The Marvell 88W8897 combined wifi and bluetooth card is known for
> > +	 * very bad bt+wifi coexisting performance.
> > +	 *
> > +	 * Decrease the passive BT Low Energy scan interval a bit
> > +	 * (0x0190 * 0.625 msec = 250 msec) and make the scan window shorter
> > +	 * (0x000a * 0,625 msec = 6.25 msec). This allows for significantly
> > +	 * higher wifi throughput while passively scanning for BT LE devices.
> > +	 */
> > +	if (id->driver_info & BTUSB_LOWER_LESCAN_INTERVAL) {
> > +		hdev->le_scan_interval = 0x0190;
> > +		hdev->le_scan_window = 0x000a;
> > +	}
> > +
>
> you can not do it this way. Modifying hci_dev internals from within the driver is not acceptable.
>
> Regards
>
> Marcel

Hi Marcel,

hmm okay, it seems to me that the intention of your commit 
bef64738e3fb87eabc6fbeededad0c44ea173384 was to allow configuring it on 
a per controller basis, also btusb changes a bunch of other hci_dev 
properties? Given that we also have to match by usb-id, I don't think 
there's another place to do that other than the usb driver, or is there?

Jonas