Re: [PATCH v1] Bluetooth: disable filter dup when scan for adv monitor

Hi Marcel,
Thanks for the comments.

On Thu, May 20, 2021 at 4:47 AM Marcel Holtmann [off-list ref] wrote:

Hi Howard,

quoted

Disable duplicates filter when scanning for advertisement monitor for
the following reasons. The scanning includes active scan and passive
scan.

For HW pattern filtering (ex. MSFT), some controllers ignore
RSSI_Sampling_Period when the duplicates filter is enabled.

For SW pattern filtering, when we're not doing interleaved scanning, it
is necessary to disable duplicates filter, otherwise hosts can only
receive one advertisement and it's impossible to know if a peer is still
in range.

can we be a bit more specific on which controller does what. I am not inclined to always disable duplicate filtering unless your controller doesn’t do what you want it to do.

Will update the commit message and submit again.

I also disagree with the last statement. If the device moved out of range (or comes back for that matter) you should get a HCI_VS_MSFT_LE_Monitor_Device_Event event that tells you if a device is in range or not.

The last statement is about software filtering, which is used when
MSFT is not supported. Software filtering in the kernel is basically
doing an LE passive scan. When the duplicate filter is enabled, some
controllers consider packets with the same address but different RSSIs
as duplicate thus not reporting to the host, which makes userspace not
able to tell if a peer is in range or not.

Device leaving:

quoted

HCI Event: LE Meta Event (0x3e) plen 43

      LE Advertising Report (0x02)
        Num reports: 1
        Event type: Non connectable undirected - ADV_NONCONN_IND (0x03)
        Address type: Random (0x01)
        Address: 01:9A:1F:C0:30:15 (Non-Resolvable)
        Data length: 31
        Flags: 0x1a
          LE General Discoverable Mode
          Simultaneous LE and BR/EDR (Controller)
          Simultaneous LE and BR/EDR (Host)
        16-bit Service UUIDs (complete): 1 entry
          Apple, Inc. (0xfd6f)
        Service Data (UUID 0xfd6f): f47698ff9243617d917ac521b5fcfd436afdb285
        RSSI: -86 dBm (0xaa)

quoted

HCI Event: Vendor (0xff) plen 18

        23 79 54 33 77 88 97 68 02 01 15 30 c0 1f 9a 01  #yT3w..h...0....
        00 00                                            ..

Device coming back:

quoted

HCI Event: Vendor (0xff) plen 18

        23 79 54 33 77 88 97 68 02 01 95 b9 0b 32 22 2a  #yT3w..h.....2"*
        00 01                                            ..

quoted

HCI Event: LE Meta Event (0x3e) plen 43

      LE Advertising Report (0x02)
        Num reports: 1
        Event type: Non connectable undirected - ADV_NONCONN_IND (0x03)
        Address type: Random (0x01)
        Address: 2A:22:32:0B:B9:95 (Non-Resolvable)
        Data length: 31
        Flags: 0x1a
          LE General Discoverable Mode
          Simultaneous LE and BR/EDR (Controller)
          Simultaneous LE and BR/EDR (Host)
        16-bit Service UUIDs (complete): 1 entry
          Apple, Inc. (0xfd6f)
        Service Data (UUID 0xfd6f): 0b861791a0fb7adcf8b45f951f7d4b7c7fc8e3fd
        RSSI: -27 dBm (0xe5)

Regards

Marcel