linux-kernel - Re: [RFC 11/19] dwc3: add OTG handling code

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Date:	Thu, 19 Mar 2015 13:08:13 +0530
From:	George Cherian <gcherianv@...il.com>
To:	Robert Baldyga <r.baldyga@...sung.com>
Cc:	balbi@...com, gregkh@...uxfoundation.org, myungjoo.ham@...sung.com,
	cw00.choi@...sung.com, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org, m.szyprowski@...sung.com
Subject: Re: [RFC 11/19] dwc3: add OTG handling code

Hi Robert,

On Wed, Mar 18, 2015 at 7:34 PM, Robert Baldyga <r.baldyga@...sung.com> wrote:
>
> This patch introduces OTG support in DWC3 driver. OTG feature is responsible
> for dynamic USB role switching (between host and peripheral modes) based
> on detected cable type.
>
> Each role switch causes complete core reinitialization. In peripheral

Do you really want to do complete core reinitialization?
While switching to HOST mode you might need to issue a LHRESET and
while switching
to Device mode make sure you re-initiallize the event buffer addresses.

If LHRESET is not used then you should do what you have done.

But I don't think adding and removing the platform_device for XHCI is
the way to go.
This might impact SoC's which really implement the OTG for DWC3.

I made an attempt on the same  and could'nt work on it more.
This still has some issues, but could be fixed.
https://lkml.org/lkml/2014/11/25/600

> mode UDC device is activated using VBUS session control mechanism. In
> host mode the new XHCI device is registered to make bus visible in system.
>
> This code is inspired by DWC3 driver from Hardkernel Linux sources [1].
>
> [1] https://github.com/hardkernel/linux.
>
> Signed-off-by: Robert Baldyga <r.baldyga@...sung.com>

Regards
-George
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