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

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Date:	Mon, 13 Jul 2015 16:55:40 +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 17:37, Sergei wrote:
> On 07/13/2015 06:02 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.
> 
> > Since the MAX3355 device doesn't
> > directly provide any vbus signals,  this shouldn't be part of the extcon driver,
> > so where should it be?
> 
>     Sure, MAX3355 does provide voltage on Vbus, controlled by -OFFVBUS input.
> It's just that the driver has only ID sensing support.
>     Do you have the MAX3355 datasheet at all?
Sorry, I meant that the max3355 device does not directly provide vbus signals
suitable for input as a gpio. Though as it provides the vbus signal to the usb
connector, there is no reason this can't be used as a gpio input to rcar (just
a level shifter needed ala the Koelsch board).

> > On the other hand, the MAX3355 has a pair of status pins that can be used
> > to get vbus instead.
> 
>     Sure, these bits reflect 4 OTG Vbus thresholds.
> 
> > If these pins aren't used for other functions, maybe
> > it's better to use these in the extcon driver.
> 
>     They are not.
My comments were based on the view that vbus output from the max3355
device wasn't a signal that could be input to the rcar via gpio. Since it is, I agree
that we should use that!

> > 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)?

> > 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?

>     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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