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

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Date:	Thu, 24 Mar 2016 08:51:04 +0200
From:	Felipe Balbi <balbi@...nel.org>
To:	John Youn <John.Youn@...opsys.com>,
	John Youn <John.Youn@...opsys.com>,
	Roger Quadros <rogerq@...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,

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.

Thank you :-)

-- 
balbi

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