linux-kernel - Re: [RFT PATCH 2/2] Revert "usb: dwc2: Fix probe problem on bcm2835"

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Date:	Wed, 16 Mar 2016 11:28:56 -0700
From:	John Youn <John.Youn@...opsys.com>
To:	Doug Anderson <dianders@...omium.org>,
	Stefan Wahren <stefan.wahren@...e.com>
CC:	Michael Niewoehner <linux@...ewoehner.de>,
	Tao Huang <huangtao@...k-chips.com>,
	Julius Werner <jwerner@...omium.org>,
	"Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	John Youn <John.Youn@...opsys.com>,
	Caesar Wang <caesar.upstream@...il.com>,
	Heiko Stuebner <heiko@...ech.de>,
	Felipe Balbi <balbi@...nel.org>,
	Remi Pommarel <repk@...plefau.lt>
Subject: Re: [RFT PATCH 2/2] Revert "usb: dwc2: Fix probe problem on bcm2835"

On 3/10/2016 11:14 AM, John Youn wrote:
> On 3/9/2016 11:06 AM, Doug Anderson wrote:
>> Stefan,
>>
>> On Wed, Mar 9, 2016 at 11:01 AM, Stefan Wahren <stefan.wahren@...e.com> wrote:
>>>
>>>> Doug Anderson <dianders@...omium.org> hat am 7. März 2016 um 22:30
>>>> geschrieben:
>>>>
>>>>
>>>> Stefan,
>>>>
>>>> On Mon, Mar 7, 2016 at 10:40 AM, Stefan Wahren <stefan.wahren@...e.com> wrote:
>>>>> Hi Doug,
>>>>>
>>>>>> Douglas Anderson <dianders@...omium.org> hat am 4. März 2016 um 19:23
>>>>>> geschrieben:
>>>>>>
>>>>>>
>>>>>> This reverts commit 192cb07f7928 ("usb: dwc2: Fix probe problem on
>>>>>> bcm2835") now that we've found the root cause. See the change
>>>>>> titled ("usb: dwc2: Add a 10 ms delay to dwc2_core_reset()").
>>>>>
>>>>> adding a delay of 10 ms after a core reset might be a idea, but applying
>>>>> both
>>>>> patches breaks USB support on RPi :-(
>>>>>
>>>>> I'm getting the wrong register values ...
>>>>
>>>> Ugh. :(
>>>>
>>>> Just out of curiosity, if you loop and time long it takes for the
>>>> registers to get to the right state after reset, what do you get?
>>>> AKA, pick:
>>>>
>>>> https://chromium-review.googlesource.com/331260
>>>>
>>>> ...and let me know what it prints out.
>>>
>>> On my Raspberry Pi B i get the following:
>>>
>>> [    2.084411] dwc2 20980000.usb: mapped PA 20980000 to VA cc880000
>>> [    2.084461] dwc2 20980000.usb: cannot get otg clock
>>> [    2.084549] dwc2 20980000.usb: registering common handler for irq33
>>> [    2.084713] dwc2 20980000.usb: Configuration mismatch. dr_mode forced to host
>>> [    2.153965] dwc2 20980000.usb: Waited 49996 us, 0x00201000 => 0x01001000,
>>> 0x00000000 => 0x02002000
>>> [    2.174930] dwc2 20980000.usb: Forcing mode to host
>>>
>>> So i changed the delay in patch #1 to msleep(50) and then both patches work like
>>> a charm.
>>
>> Great news!  :-)
>>
>> John: it's pretty clear that there's something taking almost exactly
>> 10ms on my system and almost exactly 50ms on Stefan's system.  Is
>> there some register we could poll to see when this process is done?
>> ...or can we look at the dwc2 revision number / feature register and
>> detect how long to delay?
>>
> 
> Hi Doug,
> 
> I'll have to ask around to see if anyone knows about this. And I'll
> run some tests on the platforms I have available to me as well.
> 

There's still nothing definitive on our end as to why this is
happening. Also I don't think there is any other way to poll the
reset. Our hardware engineers asked for some more information to look
into it further. Doug, Stefan, Caesar, and anyone else with a related
platform, do you know the answers to the following:

1. What is the AHB Clock frequency? Is the AHB Clock gated during
Reset?

2. Also is the PHY clock stopped during the reset or is the PHY PLL
lock times high in the order of ms?

3. In these cases, is the PHY actually an FS Transceiver and not a
UTMI/ULPI PHY?

4. Which version of the controller is being used in these cases?

Regards,
John