Re: [PATCH V2] usb: xhci: add support for performing fake doorbell

[Jon Mason <jon.mason@broadcom.com>]

On Mon, Jan 16, 2017 at 2:32 AM, Rafał Miłecki <zajec5@gmail.com> wrote:
> On 21 November 2016 at 16:31, Mathias Nyman
> <mathias.nyman@linux.intel.com> wrote:
>> On 21.11.2016 09:57, Rafał Miłecki wrote:
>>>
>>> Hi Mathias,
>>>
>>> On 17 October 2016 at 22:30, Rafał Miłecki <zajec5@gmail.com> wrote:
>>>>
>>>> From: Rafał Miłecki <rafal@milecki.pl>
>>>>
>>>> Broadcom's Northstar XHCI controllers seem to need a special start
>>>> procedure to work correctly. There isn't any official documentation of
>>>> this, the problem is that controller doesn't detect any connected
>>>> devices with default setup. Moreover connecting USB device to controller
>>>> that doesn't run properly can cause SoC's watchdog issues.
>>>>
>>>> A workaround that was successfully tested on multiple devices is to
>>>> perform a fake doorbell. This patch adds code for doing this and enables
>>>> it on BCM4708 family.
>>>>
>>>> Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
>>>> ---
>>>> V2: Enable quirk for brcm,bcm4708 machines instead of adding separated
>>>> binding
>>>>      for it. Thanks Rob for your comment on this.
>>>
>>>
>>> Do you think you can pick & push this one? V2 follows Rob's suggestion
>>> and he has some DT knowledge for sure, so I guess it should be OK.
>>> --
>>
>>
>> Is there some more background information on this?
>>
>> I don't have any contacts to Broadcom myself, adding the BMC Kernel Feedback
>> list to CC.
>> Maybe someone over there has an errata, documentation or just general
>> feedback.
>>
>> How was this workaround even figured out? ringing the doorbell for the first
>> device doesn't seem like something found by trial and error,  especially
>> when
>> xhci specs state that:
>>
>> "Software shall not write the Doorbell of an endpoint until after it has
>> issued a
>> Configure Endpoint Command for the endpoint and received a successful
>> Command
>> Completion Event."
>>
>> The whole workaround is a bit intrusive, allocating a fake device, ring a
>> doorbell for a
>> fake device in the wrong state, clearing off HSE (host system error) which
>> should only be set
>> when things really go bad, some random usleeps, and possible calling
>> xhci_start() twice.
>>
>> I can't take this as is without some more info.
>
> Hi (ping) Broadcom guys, could you help us with this USB workaround, please?

Investigating internally.  I'll let you know if I can find anything.

Thanks,
Jon

>
> --
> Rafał