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

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Date:	Tue, 22 Mar 2016 08:39:34 +0200
From:	Felipe Balbi <balbi@...nel.org>
To:	John Youn <John.Youn@...opsys.com>, 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,

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 ?

-- 
balbi

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