linux-kernel - RE: [PATCH 04/18] reset: rzv2h-usb2phy: Set VBENCTL register for OTG mode

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Message-ID:
 <TY3PR01MB1134623A14F4F313986F631ED86E0A@TY3PR01MB11346.jpnprd01.prod.outlook.com>
Date: Tue, 7 Oct 2025 11:04:04 +0000
From: Biju Das <biju.das.jz@...renesas.com>
To: Philipp Zabel <p.zabel@...gutronix.de>, Tommaso Merciai
	<tommaso.merciai.xr@...renesas.com>, Tommaso Merciai <tomm.merciai@...il.com>
CC: "linux-renesas-soc@...r.kernel.org" <linux-renesas-soc@...r.kernel.org>,
	Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>, Vinod Koul
	<vkoul@...nel.org>, Kishon Vijay Abraham I <kishon@...nel.org>, Geert
 Uytterhoeven <geert+renesas@...der.be>, magnus.damm <magnus.damm@...il.com>,
	Fabrizio Castro <fabrizio.castro.jz@...esas.com>, Prabhakar Mahadev Lad
	<prabhakar.mahadev-lad.rj@...renesas.com>, "linux-phy@...ts.infradead.org"
	<linux-phy@...ts.infradead.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 04/18] reset: rzv2h-usb2phy: Set VBENCTL register for OTG
 mode

Hi Philipp,

> -----Original Message-----
> From: Philipp Zabel <p.zabel@...gutronix.de>
> Sent: 07 October 2025 10:44
> Subject: Re: [PATCH 04/18] reset: rzv2h-usb2phy: Set VBENCTL register for OTG mode
> 
> Hi Biju,
> 
> On Di, 2025-10-07 at 04:02 +0000, Biju Das wrote:
> > Hi Philipp,
> >
> > Thanks for the feedback.
> >
> > > -----Original Message-----
> > > From: Philipp Zabel <p.zabel@...gutronix.de>
> > > Sent: 06 October 2025 17:32
> > > Subject: Re: [PATCH 04/18] reset: rzv2h-usb2phy: Set VBENCTL
> > > register for OTG mode
> > >
> > > On Mi, 2025-10-01 at 23:26 +0200, Tommaso Merciai wrote:
> > > > Add logic to set the VBENCTL register when the USB controller
> > > > operates in OTG mode. This is required to ensure proper USB
> > > > transceiver behavior when the device is configured as OTG.
> > > >
> > > > Signed-off-by: Tommaso Merciai <tommaso.merciai.xr@...renesas.com>
> > >
> > > I had reservations about this driver before, because of the opaque
> > > register initialization sequence, and I was told that no, this is a reset driver alright [1].
> >
> > The latest hardware manual document about VBENCTRL register which sets source for VBUS selection.
> > s
> 
> I still can't look at this, right? The USB2PHY control register space appears to be documented in
> the "RZ/V2H Group User's Manual: Hardware (Additional document)" (under NDA).	

It is documented here[1], Page 2177, USB2PHY Control Register (USB2m_PHY_VBENCTL)

[1]
https://www.renesas.com/en/document/mah/rzg3e-group-users-manual-hardware?r=25574493


> 
> > > Can you please try to find a proper abstraction for this, because
> > > drivers/reset is not the correct place for USB OTG mode handling.
> >
> > Sorry for the confusion. This driver is not handling USB OTG mode. It
> > just configures VBENCTRL(one time setting) that selects the source for
> > VBUS_SEL. Actual USB OTG mode handling is done USB PHY driver which sets host/device mode based on
> ID detection.
> 
> So this is a mux for the VBUS_SEL signal?

Yes, Please find the bit definition.

0 VBUS_SEL 0h RW Select VBUSEN control
0b: Output PP controlled by PORTSC1 register of the Host Controller as VBUSEN.
1b: Output VBOUT controlled by VBCTRL register of the Host Controller as VBUSEN.

We have USB PHY control driver(This driver)-> USB PHY driver->| USB HOST(Generic ehci/ohci)
                                                       	  | USB function (renesas usbhs)

We plan to set 1b for this IP in this driver for OTG channel during probe.
After that using VBOUT register the PHY driver can switch between Host and device.

> 
> Why don't the USB host controller drivers parse their "dr_mode"
> property themselves and control USB2PHY VBENCTRL via the mux API, for example?

Currently for OTG channel, based ID detection IRQ, the USB PHY driver switches between host
and device. We use method2 below for the host operation.

For Host operation:
Method1: USB2m_PHY_VBENCTL.VBUS_SEL=0
or
method2: USB2m_PHY_VBENCTL.VBUS_SEL=1 and USB_HOST_VBCTRL.VBOUT = 1

For device operation:
USB2m_PHY_VBENCTL.VBUS_SEL=1 and USB_HOST_VBCTRL.VBOUT = 0

Are you suggesting to use method1(mux) for host operation?

Currently this is one time configuration. If we plan to
use mux, then it becomes dynamic.

How we can we make use of PHY driver using mux API to select the mux register(VBUS_SEL)
in USB PHY control Driver?

Cheers,
Biju