linux-kernel - Re: [PATCH v2 4/4] usb: dwc3: Workaround for super-speed host on dra7 in dual-role mode

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Message-ID: <a5253006-0ba3-0e9d-ba8d-cc6ba0769d6c@ti.com>
Date:   Wed, 29 Mar 2017 12:57:55 +0300
From:   Roger Quadros <rogerq@...com>
To:     Felipe Balbi <balbi@...nel.org>
CC:     <vivek.gautam@...eaurora.org>, <linux-usb@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 4/4] usb: dwc3: Workaround for super-speed host on dra7
 in dual-role mode

On 28/03/17 14:10, Felipe Balbi wrote:
> 
> Hi,
> 
> Roger Quadros <rogerq@...com> writes:
>> dra7 OTG core limits the host controller to USB2.0 (high-speed) mode
>> when we're operating in dual-role.
> 
> yeah, that's not a quirk. DRA7 supports OTGv2, not OTGv3. There was no
> USB3 when OTGv2 was written.
> 
> DRA7 just shouldn't use OTG core altogether. In fact, this is the very
> thing I've been saying for a long time. Make the simplest implementation
> possible. The dead simple, does-one-thing-only sort of implementation.
> 
> All we need for Dual-Role (without OTG extras) is some input for ID and
> VBUS, then we add/remove HCD/UDC conditionally and set PRTCAPDIR.
> 

The catch is that on AM437x there is no way to get ID and VBUS events other
than the OTG controller so we have to rely on the OTG controller for that. :(

I agree on the simplicity part. Let's do what minimal is necessary first.

cheers,
-roger