linux-kernel - RE: [PATCH v3] phy: rcar-gen2 usb: Add Host/Function switching for USB0

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Date:	Mon, 13 Jul 2015 17:44:09 +0000
From:	Phil Edworthy <phil.edworthy@...esas.com>
To:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
	"Kishon Vijay Abraham I" <kishon@...com>
CC:	Rob Herring <robh+dt@...nel.org>, Pawel Moll <pawel.moll@....com>,
	"Mark Rutland" <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-sh@...r.kernel.org" <linux-sh@...r.kernel.org>
Subject: RE: [PATCH v3] phy: rcar-gen2 usb: Add Host/Function switching for
 USB0

Hi Sergei,

On 13 July 2015 18:10, Sergei wrote:
> On 07/13/2015 07:55 PM, Phil Edworthy wrote:
> 
> >>>>>>> Instead of statically selecting the PHY connection to either the
> >>>>>>> USBHS (Function) or PCI0 (Host) IP blocks, this change allows the
> >>>>>>> dts to specifiy gpio pins for the vbus and id signals. Additional
> 
> >>>>>>        These GPIOs don't have anything to do with the PHY, they're
> interfacing
> 
> >>>>       Perhaps that was too strong statement but nevertheless...
> 
> >>> Looking at your MAX3355 extcon driver, I can't see how it would work on it's
> >>> own.
> 
> >>      I've added the 'extcon' support into the Renesas USBHS driver, so that it
> >> should be able to sense the ID pin status.
> 
> >>> The system needs to sense vbus in order to determine that the board
> >>> has been plugged into a USB Host.
<snip>
Ok, so in summary, the max3355 device has two ways to communicate vbus
back to a processor. You can either use the vbus signal or the status1/2 signals
connected as gpios. The status1/2 signals give HNP information for OTG and
are preferred, but depending on the board, they might not be available.

 
> >>> My intention is to make the USB PHY driver listen for extcon events instead
> >>> of directly accessing the ID and VBUS signals, but otherwise behave in the
> >>> same way it currently does.
> 
> >>      I'm not sure the PHY driver should be interested in that...
> 
> > Then how is the PHY going to know when to switch between pci0 (host) and
> > hsusb (function)?
> 
>     As I said, I planted the extcon hooks directly into USBHS (merged patch)
> and USB HCD code (unmerged, low quality hack).
Unless I am missing something, the problem I see with this is that it will not
dynamically switch between Host and Gadget, hence my suggestion that the
USB PHY driver be interested in the extcon events.


> >>> After reading some other threads, I also intend to set up a fixed regulator
> >>> for the MAX3355 device to setup the shutdown and vbus enable pins.  I
> know
> >>> that the vbus enable should really be controlled some other way depending
> >>> on the role, but for the moment I think it's ok just to enable it always.
> 
> >>      It's OK only in the host mode.
> >>      I don't think we need regulators. SHDN- is already supported by the driver
> >> (though it only drives it high at start-up time), in fact it was the only reason
> >> not to use gpio.
> 
> >>> Do you think that is the correct way to progress this?
> 
> >>      I didn't have a clear picture how to implement the OTG support at the time
> >> of writing the MAX3355 driver; actually, I was tasked to only support ID p[in
> >> sensing.
> 
> > Right, so the max3355 driver needs some changes to include vbus handling.
> > Are you working on this, or should I take it on?
> 
>     No, not working yet, I have other things on my plate still...
Ok, thanks for your comments! Hopefully I'll find the time to have a stab at this.


> >>      Note that there's some ongoing effort now on linux-usb to support OTG
> >> functionality.
> 
> > Yes, I need to spend some time reading that list!
> 
> > Thanks
> > Phil
> 
> WBR, Sergei

Thanks
Phil
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