linux-kernel - Re: [PATCH 1/2] usb: dwc3: core: Introduce dwc3_device

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Message-ID: <87r3eqg1us.fsf@intel.com>
Date:	Thu, 31 Mar 2016 17:26:35 +0300
From:	Felipe Balbi <balbi@...nel.org>
To:	Roger Quadros <rogerq@...com>, John Youn <John.Youn@...opsys.com>
Cc:	"nsekhar\@ti.com" <nsekhar@...com>,
	"linux-usb\@vger.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] usb: dwc3: core: Introduce dwc3_device_reinit()


Hi,

Roger Quadros <rogerq@...com> 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@...com>
>>>>>>>>>
>>>>>>>>> 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
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
Run/Stop was in a metastable state, considering that Run/Stop signal is
not visible outside the die ?

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

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

-- 
balbi

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