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

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Date:	Thu, 31 Mar 2016 17:02:59 +0300
From:	Roger Quadros <rogerq@...com>
To:	John Youn <John.Youn@...opsys.com>, Felipe Balbi <balbi@...nel.org>
CC:	"nsekhar@...com" <nsekhar@...com>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] usb: dwc3: core: Introduce dwc3_device_reinit()

On 30/03/16 21:44, John Youn wrote:
> On 3/23/2016 11:52 PM, Felipe Balbi wrote:
>>
>> Hi,
>>
>> John Youn <John.Youn@...opsys.com> writes:
>>> [ text/plain ]
>>> On 3/21/2016 11:40 PM, Felipe Balbi wrote:
>>>>
>>>> Hi,
>>>>
>>>> John Youn <John.Youn@...opsys.com> writes:
>>>>> [ text/plain ]
>>>>> On 3/18/2016 12:17 PM, John Youn wrote:
>>>>>> On 3/16/2016 6:56 AM, Felipe Balbi wrote:
>>>>>>>
>>>>>>> heh, +john
>>>>>>>
>>>>>>> Felipe Balbi <balbi@...nel.org> writes:
>>>>>>>> [ text/plain ]
>>>>>>>>
>>>>>>>> Hi,
>>>>>>>>
>>>>>>>> Roger Quadros <rogerq@...com> writes:
>>>>>>>>> [ text/plain ]
>>>>>>>>> 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?

cheers,
-roger