linux-kernel - Re: [PATCH RESEND V4 5/9] of: Add NVIDIA Tegra xHCI controller binding

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Date:	Thu, 30 Oct 2014 18:24:35 +0100
From:	Thierry Reding <thierry.reding@...il.com>
To:	Andrew Bresticker <abrestic@...omium.org>
Cc:	Stephen Warren <swarren@...dotorg.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	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>,
	Russell King <linux@....linux.org.uk>,
	Jassi Brar <jassisinghbrar@...il.com>,
	Linus Walleij <linus.walleij@...aro.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Mathias Nyman <mathias.nyman@...el.com>,
	Grant Likely <grant.likely@...aro.org>,
	Alan Stern <stern@...land.harvard.edu>,
	Arnd Bergmann <arnd@...db.de>,
	Kishon Vijay Abraham I <kishon@...com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>
Subject: Re: [PATCH RESEND V4 5/9] of: Add NVIDIA Tegra xHCI controller
 binding

On Thu, Oct 30, 2014 at 10:19:21AM -0700, Andrew Bresticker wrote:
> On Thu, Oct 30, 2014 at 6:55 AM, Thierry Reding
> <thierry.reding@...il.com> wrote:
> > On Wed, Oct 29, 2014 at 09:37:14AM -0700, Andrew Bresticker wrote:
> >> On Wed, Oct 29, 2014 at 2:43 AM, Thierry Reding
> >> <thierry.reding@...il.com> wrote:
> >> > On Tue, Oct 28, 2014 at 03:27:50PM -0700, Andrew Bresticker wrote:
> >> > [...]
> >> >> diff --git a/Documentation/devicetree/bindings/pinctrl/nvidia,tegra124-xusb-padctl.txt b/Documentation/devicetree/bindings/pinctrl/nvidia,tegra124-xusb-padctl.txt
> >> > [...]
> >> >> +Optional properties:
> >> >> +-------------------
> >> >> +- vbus-{0,1,2}-supply: VBUS regulator for the corresponding UTMI pad.
> >> >> +- vddio-hsic-supply: VDDIO regulator for the HSIC pads.
> >> >> +- nvidia,usb3-port-{0,1}-lane: PCIe/SATA lane to which the corresponding USB3
> >> >> +  port is mapped.  See <dt-bindings/pinctrl/pinctrl-tegra-xusb.h> for the list
> >> >> +  of valid values.
> >> >
> >> > I dislike how we now need to provide a list of all pins in the header
> >> > file, where previously we used strings for this. This could become very
> >> > ugly if the set of pins changes in future generations of this IP block.
> >> >
> >> > Could we instead derive this from the pinmux nodes? For example you have
> >> > this in the example below:
> >> >
> >> >         usb3p0 {
> >> >                 nvidia,lanes = "pcie-0";
> >> >                 ...
> >> >         };
> >> >
> >> > Perhaps what we need is to either key off the node name or add another
> >> > property, such as:
> >> >
> >> >         nvidia,usb3-port = <0>;
> >> >
> >> > This would match the nvidia,usb2-port property that you've added below.
> >>
> >> That is actually how I described the USB3 port to SS lane mapping
> >> originally, but in review of an earlier version of this series,
> >> Stephen suggested that I make it a separate, not pinconfig property
> >> since it wasn't a value written directly to the hardware.  I'm fine
> >> with changing it back as the pinconfig property makes more sense to me
> >> as well.
> >
> > Hmm... I had considered it a mux option of the specific lane. If the
> > function is usb3, it'd still need to be muxed to one of the ports. So
> > it's additional information associated with the usb3 function.
> >
> > I did look through the driver changes and can't really make out which
> > part of the code actually performs this assignment. Can you point me to
> > it?
> 
> There's not really an assignment.  The property is used to map between
> a lane (e.g. PCIe-0 or SATA) and the USB3.0 port it's mapped to.  For
> an example of where it's used, take a look at usb3_phy_power_on().
> There are certain per-lane registers which need to be programmed in
> addition to the per-USB3.0 port pad registers.  This mapping is used
> to determine which lane needs to be programmed.

Are you saying the mapping of lane to USB port is fixed? That is, PCIe-0
lane is always used for USB port X and SATA always for USB port Y?

If so I'd argue that we don't need this property in DT at all.

Thierry

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