linux-kernel - Re: [Patch V2 01/18] dt-bindings: phy: tegra-xusb: Add usb-role-switch

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Message-ID: <20200113150656.GB2436168@ulmo>
Date:   Mon, 13 Jan 2020 16:06:56 +0100
From:   Thierry Reding <thierry.reding@...il.com>
To:     Nagarjuna Kristam <nkristam@...dia.com>
Cc:     JC Kuo <jckuo@...dia.com>, balbi@...nel.org,
        gregkh@...uxfoundation.org, jonathanh@...dia.com,
        mark.rutland@....com, robh+dt@...nel.org, kishon@...com,
        devicetree@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [Patch V2 01/18] dt-bindings: phy: tegra-xusb: Add
 usb-role-switch

On Mon, Jan 13, 2020 at 10:07:08AM +0530, Nagarjuna Kristam wrote:
> 
> On 10-01-2020 16:46, Thierry Reding wrote:
> > On Fri, Dec 20, 2019 at 04:08:30PM +0800, JC Kuo wrote:
> > > On 12/19/19 9:05 PM, Thierry Reding wrote:
> > > > On Wed, Dec 18, 2019 at 02:46:14PM +0530, Nagarjuna Kristam wrote:
> > > > > Add usb-role-switch property for Tegra210 and Tegra186 platforms. This
> > > > > entry is used by XUSB pad controller driver to register for role changes
> > > > > for OTG/Peripheral capable USB 2 ports.
> > > > > 
> > > > > Signed-off-by: Nagarjuna Kristam<nkristam@...dia.com>
> > > > > ---
> > > > > V2:
> > > > >   - Moved usb-role-switch to seperate Required section as suggested by Thierry.
> > > > >   - Added reference to usb/usb-conn-gpio.txt for connector subnode.
> > > > > ---
> > > > >   .../devicetree/bindings/phy/nvidia,tegra124-xusb-padctl.txt         | 6 ++++++
> > > > >   1 file changed, 6 insertions(+)
> > > > > 
> > > > > diff --git a/Documentation/devicetree/bindings/phy/nvidia,tegra124-xusb-padctl.txt b/Documentation/devicetree/bindings/phy/nvidia,tegra124-xusb-padctl.txt
> > > > > index 9fb682e..23bf354 100644
> > > > > --- a/Documentation/devicetree/bindings/phy/nvidia,tegra124-xusb-padctl.txt
> > > > > +++ b/Documentation/devicetree/bindings/phy/nvidia,tegra124-xusb-padctl.txt
> > > > > @@ -174,6 +174,12 @@ Required properties:
> > > > >     - "device": for USB device mode
> > > > >     - "otg": for USB OTG mode
> > > > > +Required properties for OTG/Peripheral capable USB2 ports:
> > > > > +- usb-role-switch: Boolean property to indicate that the port support OTG or
> > > > "supports", and also, why if it supports OTG*or*  peripheral? Doesn't
> > > > OTG imply peripheral? OTG means it can be either peripheral or host,
> > > > right? So I think the end of that sentence can be just:
> > > > 
> > > > 	"... the port supports OTG."
> > > An USB OTG port is capable of both USB host and peripheral operations. An USB
> > > peripheral port can only act as an USB peripheral.
> > > 
> > > The micro USB ports found on Jetson TX1/TX2 platforms are micro-AB ports which
> > > should implement both host and peripheral capabilities. We say such ports
> > > support OTG. The micro USB port found on Jetson Nano is a micro-B port which
> > > should implement peripheral capability only. We say such ports support
> > > peripheral, rather than OTG.
> > I the port supports only peripheral mode, why do we need to have a
> > usb-role-switch property? Shouldn't we in that case have a mode property
> > with value "device"?
> > 
> > usb-mode-switch is only needed if mode = "otg", isn't it? In all other
> > cases the functionality is fixed (either host or peripheral) and the
> > mode cannot be switched.
> > 
> > Thierry
> 
> usb-role-switch is needed when mode == "otg" or "peripheral".
> 
> Device mode is detected via vbus GPIO irrespective of mode being peripheral
> only or OTG.
> Host mode is detected via id-gpio, in OTG case.
> 
> When mode is peripheral, role changes happens between USB_ROLE_DEVICE and
> USB_ROLE_NONE, which are generally based on Vbus GPIO(hot plug) detection.
> 
> When mode is otg, role changes happens between USB_ROLE_HOST,
> USB_ROLE_DEVICE and USB_ROLE_NONE, which are detected via id-gpio, vbus-gpio
> and no detection respectively.

Right, that makes perfect sense. Thanks for putting it so clearly. With
the "support" -> "supports" typo fixed, this patch:

Acked-by: Thierry Reding <treding@...dia.com>

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