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