[PATCH v3 2/3] ARM: dts: bcm2837-rpi-3-b: Add bcm43438 as serial slave

Eric Anholt eric at anholt.net
Thu Aug 17 09:21:12 PDT 2017

Marcel Holtmann <marcel at holtmann.org> writes:

> Hi Loic,
>>>>> < HCI Command: Broadcom Write UART Clock Setting (0x3f|0x0045) plen 1
>>>>>        01                                               .
>>>>>> HCI Event: Command Complete (0x0e) plen 4
>>>>>      Broadcom Write UART Clock Setting (0x3f|0x0045) ncmd 1
>>>>>        Status: Unknown HCI Command (0x01)
>>>>> And I am seeing fun stuff like failed frame assembly.
>>>>> [  888.687594] Bluetooth: hci0: BCM: chip id 94
>>>>> [  888.687821] Bluetooth: hci0: BCM43430A1 (001.002.009) build 0182
>>>>> [  892.059023] Bluetooth: hci0: Frame reassembly failed (-84)
>>>>> [  892.316936] Bluetooth: hci0: BCM: failed to write clock (-56)
>>>>> [  892.429478] Bluetooth: hci0: BCM (001.002.009) build 0182
>>>>> Actually not providing the firmware makes the controller work. It however is stuck ad AA:AA:.. default address. Providing the firmware turns the address active. However then it never completes.
>>>> I've tried on and off to get the BT working, there seems to lots of
>>>> options and bits needed including some patches to the bluez [1] stuff
>>>> but between not quite upstream kernel bits and numerous distros all
>>>> doing it slightly differently I've never got it to work well.
>>>> The yocto [1] bits seem fairly representative of some the patches
>>>> flying around "to get it working" although I'm not sure how many of
>>>> these are actually required and how many are superfluous with this
>>>> patch set. There seems to be a firmware required that's not
>>>> distributed with linux-firmware which would also be nice to resolve.
>>> Non of these Yocto patches are actually needed. The culprit is the .oper_speed setting to be 4Mbps. Once you reduce that to 921600 thing will start to work smoothly. I sent a patch that takes the .oper_speed out completely and only applies it for the ACPI based devices where we know that it works.
>>> With my patch and the right DT entries for uart0 it actually works with “btattach -B /dev/ttyAMA0 -P bcm”. It will load the firmware, configure it and head towards the right path.
>>> Obviously btattach is only an interim step here. Loic’s patches for serdev integration and changing the DT to expose uart0 as serial-slave for Bluetooth is the right approach. Once Loic’s resends the patches we can get them into bluetooth-next and start merging these towards upstream. After that, Bluetooth should work just out of the box like with any USB dongle.
>>> And the Yocto patches should be abandoned. If using H:5 (aka 3-Wire) instead of H:4 is possible, we could consider it, but as long as the UART wiring doesn’t cause any bit errors, it is not worth it.
>>> That said, I do see a "Bluetooth: hci0: Frame reassembly failed (-84)” error. I need to figure out where that is. Frankly we really need to hexdump the packet when this happens.
>> I also meet this Frame reassembly failure, Seems we receive a 0x00 byte from the controller (unknown pkt type).
> that means adding something like this will silence it.
> +#define BCM_RECV_NULL \
> +       .type = 0x00, \
> +       .hlen = 0, \
> +       .loff = 0, \
> +       .lsize = 0, \
> +       .maxlen = 0
> +
> +static int bcm_recv_null(struct hci_dev *hdev, struct sk_buff *skb)
> +{
> +       kfree_skb(skb);
> +       return 0;
> +}
> +
>  static const struct h4_recv_pkt bcm_recv_pkts[] = {
>         { H4_RECV_ACL,      .recv = hci_recv_frame },
>         { H4_RECV_SCO,      .recv = hci_recv_frame },
>         { H4_RECV_EVENT,    .recv = hci_recv_frame },
>         { BCM_RECV_LM_DIAG, .recv = hci_recv_diag  },
> +       { BCM_RECV_NULL,    .recv = bcm_recv_null  },
>  };
> It does silence it indeed. Maybe this is some of their markers to
> ensure that the baud rate change worked. Or it is the indication that
> the reset completed. Do you happen to know between which commands we
> receive it?
>> Regarding the speed, I'm unable to reach 3Mbps, I selected 921600
>> because this is the baudrate used by raspbian bt script.
> That is the same I experienced. The 921600 works fine, but trying
> 3Mbps doesn’t. However it seems with hciattach you can crank it up to
> 3Mpbs somehow. Maybe the delay is just to short for the UART switching
> in that case.
>> Maybe they had some issues at higher speed (empirical value ?),
>> However 2Mbps seems ok on my side (need to double check/adjust).
> We have to make it a DT max-speed param anyway. So I am not that
> worried.
>> In a second step, need to check If we can use hardware flow control,
>> I heard that pin 16&17 are routed to the bcm RTS/CTS.  Since there is
>> no DMA usage, it could help.

The BT's CTS/RTS are tied to 3v3/ground.

> Eric, any chance you can dig out the recommendation for the Bluetooth
> controller usage? I would also like to see the recommended PCM
> settings for this hardware. It bet it is somehow wired up to the sound
> controller.

BT's PCM is connected to gpio 28-31 on the pi3, which you can pinmux to
the i2s controller (pcm_gpio28 pin group).

I'm not clear on what you're asking for, or where I would go to find
anything else.  However, for integration stuff on the board, Phil, Dom,
and Gordon at RPi are likely to know more.
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