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

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Date:   Fri, 17 Sep 2021 14:36:50 +0200
From:   Jonas Dreßler <verdre@...d.nl>
To:     Pali Rohár <pali@...nel.org>
Cc:     Amitkumar Karwar <amitkarwar@...il.com>,
        Ganapathi Bhat <ganapathi017@...il.com>,
        Xinming Hu <huxinming820@...il.com>,
        Kalle Valo <kvalo@...eaurora.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Marcel Holtmann <marcel@...tmann.org>,
        Johan Hedberg <johan.hedberg@...il.com>,
        Luiz Augusto von Dentz <luiz.dentz@...il.com>,
        Tsuchiya Yuto <kitakar@...il.com>,
        linux-wireless@...r.kernel.org, linux-bluetooth@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Maximilian Luz <luzmaximilian@...il.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Subject: Re: [PATCH] Bluetooth: btusb: Lower passive lescan interval on
 Marvell 88W8897

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@...d.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
>>