Re: [PATCH 1/2] usb: dwc3: core: Introduce dwc3_device_reinit()

[Roger Quadros]

+Abhishek, Ravi,

Felipe,

On 31/03/16 17:26, Felipe Balbi wrote:
> 
> Hi,
> 
> Roger Quadros <rogerq@xxxxxx> writes:
>>>>>>>>>>> We will need this function for a workaround.
>>>>>>>>>>> The function issues a softreset only to the device
>>>>>>>>>>> controller and performs minimal re-initialization
>>>>>>>>>>> so that the device controller can be usable.
>>>>>>>>>>>
>>>>>>>>>>> As some code is similar to dwc3_core_init() take out
>>>>>>>>>>> common code into dwc3_get_gctl_quirks().
>>>>>>>>>>>
>>>>>>>>>>> We add a new member (prtcap_mode) to struct dwc3 to
>>>>>>>>>>> keep track of the current mode in the PRTCAPDIR register.
>>>>>>>>>>>
>>>>>>>>>>> Signed-off-by: Roger Quadros <rogerq@xxxxxx>
>>>>>>>>>>
>>>>>>>>>> I must say, I don't like this at all :-p There's ONE known silicon which
>>>>>>>>>> needs this because of a poor silicon integration which took an IP with a
>>>>>>>>>> known erratum where it can't be made to work on lower speeds and STILL
>>>>>>>>>> was integrated without a superspeed PHY.
>>>>>>>>>>
>>>>>>>>>> There's a reason why I never tried to push this upstream myself ;-)
>>>>>>>>>>
>>>>>>>>>> I'm really thinking we might be better off adding a quirk flag to skip
>>>>>>>>>> the metastability workaround and allow this ONE silicon to set the
>>>>>>>>>> controller to lower speed.
>>>>>>>>>>
>>>>>>>>>> John, can you check with your colleagues if we would ever fall into
>>>>>>>>>> STAR#9000525659 if we set maximum speed to high speed during driver
>>>>>>>>>> probe and never touch it again ? I would assume we don't really fall
>>>>>>>>>> into the metastability workaround, right ? We're not doing any sort of
>>>>>>>>>> PM for dwc3...
>>>>>>>>>>
>>>>>>>
>>>>>>> Hi Felipe,
>>>>>>>
>>>>>>> Do you mean to keep DCFG.speed to SS and set dwc->maximum_speed to HS?
>>>>>>> I don't see an issue with that as long as we always ignore
>>>>>>> dwc->maximum_speed when programming DCFG.speed for all affected
>>>>>>> versions of the core. As long as the DCFG.speed = SS, you should not
>>>>>>> hit the STAR.
>>>>>>
>>>>>> I actually mean changing DCFG.speed during driver probe and never
>>>>>> touching it again. Would that still cause problems ?
>>>>>>
>>>>>
>>>>> In that case I'm not sure. The engineer who would know is off until
>>>>> next week so I'll get back to you as soon as I can talk to him about
>>>>> it.
>>>>
>>>
>>> So the engineers said that this issue can occur while set to HS and
>>> the run/stop bit is changed so it seems that won't work.
>>
>> Thanks John.
>>
>> Felipe,
>>
>> any suggestion how we can fix this upstream?
> 
> no idea, I don't have a lot of memory about this problem. I really don't
> remember the details about this, is there an openly available errata
> document which I could read ? /me goes search for it.
> 
> I found [1] which tells me, the following:
> 
> 
> | i819        | A Device Control Bit Meta-Stability for USB3.0 Controller in USB2.0 Mode   |
> |-------------+----------------------------------------------------------------------------|
> | Criticality | Medium                                                                     |
> |             |                                                                            |
> | Descritiion | When USB3.0 controller core is programmed to be a USB 2.0-only device      |
> |             | hardware meta-stability on USB_DCTL[31]RUNSTOP bit causing the core to     |
> |             | attempt high speed as well as SuperSpeed connection or completely miss     |
> |             | the attach request.                                                        |
> |             |                                                                            |
> | Workaround  | If the requirement is to always function in USB 2.0 mode, there is no      |
> |             | workaround.                                                                |
> |             | Otherwise, you can always program the USB controller core to be SuperSpeed |
> |             | 3.0 capable (USB_DCFG[2:0]DEVSPD = 0x4)                                    |
> |             |                                                                            |
> | Revisions   | SR 1.1, 2.0                                                                |
> | Impacted    |                                                                            |
> |-------------+----------------------------------------------------------------------------|
> 
> So, TI's own documentation says that there is _no_ workaround. My

We are working on updating that document. Apparently Synopsis has suggested this workaround.
pasting verbatim

"
-          As last step of device configuration we set the RUNSTOP bit in DCTL.

-          Once we set the RUNSTOP bit, we need to monitor GDBGLTSSM for 100 ms until one of the two below happens:.

	o   We see the GDBGLTSSM.LTDB_LINK_STATE changing from 4

	o   We receive the USB 2.0 reset interrupt.

If none of above happens then we can stop monitoring it.

-          If state change from 4 occurs issue a SoftReset thru DCTL.CSftRst and reconfigure Device. This time it is guaranteed that no metastability will occur so no need to do the 100ms timeout.
"

> question is, then: How are you sure that resetting the device actually
> solves the issue ? Did you really hit the metastability problem and
> noted that it works after a soft-reset ? How did you verify that

I don't know if it solves the issue or not. It was suggested by Synopsis to TI's silicon team.
I never hit the metastability problem detection condition in my overnight tests (i.e. LTDB_LINK_STATE != 4).
I have verified that things work after a soft-reset by faking that the error happens.

> Run/Stop was in a metastable state, considering that Run/Stop signal is
> not visible outside the die ?

LTDB_LINK_STATE != 4 within 100ms or RUNSTOP set is the condition to detect that the issue occurred.

> 
> It seems to me that resetting the IP is just as "dangerous" as setting
> the IP to High-speed in the first place. No ?

The soft-reset is just a recovery mechanism if that error is ever hit.
Putting the controller in reset state means it is in a known state. Why do you say it
would be dangerous?

The original workaround i.e. setting the High-speed instance to Super-speed to avoid this errata
is causing another side effect. i.e. erratic interrupts happen and more than 2 seconds delay
to enumerations. This problem is more serious and so we have to keep the controller in
High-speed and tackle the meta-stability condition if it happens.

cheers,
-roger

> 
> [1] http://www.ti.com/lit/er/sprz429h/sprz429h.pdf
>