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

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Date:	Wed, 23 Mar 2016 17:40:14 -0700
From:	John Youn <John.Youn@...opsys.com>
To:	Felipe Balbi <balbi@...nel.org>,
	John Youn <John.Youn@...opsys.com>,
	"Roger Quadros" <rogerq@...com>
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 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.

Regards,
John