Messages in this thread | | | Subject | Re: [PATCH] Bluetooth: btusb: Lower passive lescan interval on Marvell 88W8897 | From | Jonas Dreßler <> | Date | Fri, 17 Sep 2021 14:36:50 +0200 |
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On 9/17/21 2:30 PM, Pali Rohár wrote: > On Friday 17 September 2021 14:27:18 Jonas Dreßler wrote: >> 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. > > Hello! Do you know if this issue is specific only to this one Marvell > 88W8897 chip or if this issue affects also other Marvell wifi+bt combo > chips?
Hi! No idea, good question, but I don't own any other devices with Marvell chips. Maybe it's even safe to apply it to all Bluetooth devices, I guess less scanning load is good for everyone (as long as it doesn't impact the scanning results of course, so that would need testing).
> >> 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@v0yd.nl> >> --- >> 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; >> + } >> + >> if (IS_ENABLED(CONFIG_BT_HCIBTUSB_MTK) && >> (id->driver_info & BTUSB_MEDIATEK)) { >> hdev->setup = btusb_mtk_setup; >> -- >> 2.31.1 >>
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