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

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Message-ID: <CACna6ryJ7fod1KUOa9BVuQQWpCKg0_ArtMzHq_P5xYfW9Namxw@mail.gmail.com>
Date:   Mon, 16 Jan 2017 08:32:45 +0100
From:   Rafał Miłecki <zajec5@...il.com>
To:     Mathias Nyman <mathias.nyman@...ux.intel.com>,
        Jon Mason <jon.mason@...adcom.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        BCM Kernel Feedback <bcm-kernel-feedback-list@...adcom.com>
Cc:     Mathias Nyman <mathias.nyman@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Hauke Mehrtens <hauke@...ke-m.de>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Rafał Miłecki <rafal@...ecki.pl>
Subject: Re: [PATCH V2] usb: xhci: add support for performing fake doorbell

On 21 November 2016 at 16:31, Mathias Nyman
<mathias.nyman@...ux.intel.com> wrote:
> On 21.11.2016 09:57, Rafał Miłecki wrote:
>>
>> Hi Mathias,
>>
>> On 17 October 2016 at 22:30, Rafał Miłecki <zajec5@...il.com> wrote:
>>>
>>> From: Rafał Miłecki <rafal@...ecki.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@...ecki.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?

-- 
Rafał