linux-kernel - Re: [PATCH 1/2] usb: dwc3: gadget: Fix full speed mode

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Date:   Tue, 20 Dec 2016 14:23:38 +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:     "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: gadget: Fix full speed mode


Hi,

John Youn <John.Youn@...opsys.com> writes:
> On 12/7/2016 7:06 PM, John Youn wrote:
>> On 12/7/2016 4:44 AM, Felipe Balbi wrote:
>>>
>>> Hi,
>>>
>>> Roger Quadros <rogerq@...com> writes:
>>>>>> Roger Quadros <rogerq@...com> writes:
>>>>>>> DCFG.DEVSPD == 0x3 is not valid and we need to set
>>>>>>> DCFG.DEVSPD to 0x1 for full speed mode.
>>>>>>
>>>>>> seems like it has been made invalid somewhere between 1.73a and
>>>>>> 2.60a. Can you figure it out from Documentation why and when it was made
>>>>>> invalid? We might need revision checks here.
>>>>>>
>>>>>
>>>>> I'll try to dig out more.
>>>>
>>>> I couldn't figure out more information on this. The changelogs in the TRMs
>>>> don't capture this change and I don't have access to all TRM versions
>>>> so I can't say which version it got changed and why.
>>>>
>>>> Can we please involve someone from Synopsis to provide this information?
>>>> Thanks.
>>>
>>> John, could you help us with this query? We'd like to understand why one
>>> of the FULLSPEED modes got removed. Do we need a revision check or can
>>> we assume that the other mode was never supposed to be used?
>>>
>> 
>> Full speed is 0x1. 0x3 may still work due to how the bits are
>> checked. But it definitely should be 0x1.
>> 
>> I'm not sure if it was 0x3 before. I still need to confirm whether
>> that was the case or not and if so why.
>> 
>
> Hi Felipe,
>
> According to the old databook, 0x3 was for FS in 48MHz mode for 1.1
> transceiver, which was never supported. UTMI FS was still specified as
> 0x1 in those old databooks.

Thank you, so Roger we should actually completely remove FULLSPEED
setting of 0x3. Can you update the patch accordingly?

-- 
balbi

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