[3/8] dt-bindings: phy: tegra-xusb-padctl: Add nvidia,usb3-port-fake entry

[Thierry Reding <thierry.reding@gmail.com>]

On Wed, Feb 13, 2019 at 04:08:15PM +0530, Nagarjuna Kristam wrote:
> 
> 
> On 04-02-2019 17:18, Thierry Reding wrote:
> > On Thu, Jan 03, 2019 at 03:34:54PM +0530, Nagarjuna Kristam wrote:
> >> Add binding details regarding nvidia,usb3-port-fake
> >>
> >> Signed-off-by: Nagarjuna Kristam <nkristam@nvidia.com>
> >> ---
> >>  Documentation/devicetree/bindings/phy/nvidia,tegra124-xusb-padctl.txt | 3 +++
> >>  1 file changed, 3 insertions(+)
> >>
> >> diff --git a/Documentation/devicetree/bindings/phy/nvidia,tegra124-xusb-padctl.txt b/Documentation/devicetree/bindings/phy/nvidia,tegra124-xusb-padctl.txt
> >> index 3742c15..21a5541 100644
> >> --- a/Documentation/devicetree/bindings/phy/nvidia,tegra124-xusb-padctl.txt
> >> +++ b/Documentation/devicetree/bindings/phy/nvidia,tegra124-xusb-padctl.txt
> >> @@ -158,6 +158,9 @@ Optional properties:
> >>    is internal. In the absence of this property the port is considered to be
> >>    external.
> >>  - vbus-supply: phandle to a regulator supplying the VBUS voltage.
> >> +- nvidia,usb3-port-fake: A integer property whose presense informs that a
> >> +  fake USB3 port needs to be mapped for corresponding USB2 port. This entry
> >> +  is applicable only for Tegra210 based platforms which has USB2 only ports.
> > 
> > You don't provide a rationale fo why this fake USB3 port needs to be
> > specified. Doesn't the OTG port work without the fake USB3 port? Why
> > does it need to be specified and which one should be used as fake?
> > 
> 
> Yes, on Tegra210 based platforms, USB2 only device/OTG ports don't work
> 
> > You mention elsewhere that an unused USB3 port is used on Jetson TX1,
> > but what if there are no unused ports on a platform? Can we use any
> > USB3 port for this purpose?
> > 
> 
> If we dont have any unused port, we cannot get device mode working on USB2 only port.
> We cannot use any USB3 port, we need to use an un-used USB3 port, so that we can
> fake that corresponding USB2 only port as USB2 and USB3 port.

Hm... seems to me like we should be able to do this without an extra
device tree property. Surely we can determine at runtime which of the
ports are actually unused and pick one? If it doesn't matter which one,
we can just pick the first one that's unused, or an unused one at
random.

Thierry