linux-kernel - Re: [PATCH V5 11/16] dt-bindings: PHY: P2U: Add Tegra 194 P2U block

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Date:   Fri, 26 Apr 2019 18:07:23 +0200
From:   Thierry Reding <thierry.reding@...il.com>
To:     Rob Herring <robh@...nel.org>
Cc:     Vidya Sagar <vidyas@...dia.com>, lorenzo.pieralisi@....com,
        bhelgaas@...gle.com, mark.rutland@....com, jonathanh@...dia.com,
        kishon@...com, catalin.marinas@....com, will.deacon@....com,
        jingoohan1@...il.com, gustavo.pimentel@...opsys.com,
        mperttunen@...dia.com, linux-pci@...r.kernel.org,
        devicetree@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        kthota@...dia.com, mmaddireddy@...dia.com, sagar.tv@...il.com
Subject: Re: [PATCH V5 11/16] dt-bindings: PHY: P2U: Add Tegra 194 P2U block

On Fri, Apr 26, 2019 at 10:45:19AM -0500, Rob Herring wrote:
> On Wed, Apr 24, 2019 at 10:49:59AM +0530, Vidya Sagar wrote:
> > Add support for Tegra194 P2U (PIPE to UPHY) module block which is a glue
> > module instantiated one for each PCIe lane between Synopsys Designware core
> > based PCIe IP and Universal PHY block.
> 
> Missing Sob.
> 
> > ---
> > Changes since [v4]:
> > * None
> > 
> > Changes since [v3]:
> > * None
> > 
> > Changes since [v2]:
> > * Changed node label to reflect new format that includes either 'hsio' or
> >   'nvhs' in its name to reflect which UPHY brick they belong to
> > 
> > Changes since [v1]:
> > * This is a new patch in v2 series
> > 
> >  .../bindings/phy/phy-tegra194-p2u.txt         | 28 +++++++++++++++++++
> >  1 file changed, 28 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/phy/phy-tegra194-p2u.txt
> > 
> > diff --git a/Documentation/devicetree/bindings/phy/phy-tegra194-p2u.txt b/Documentation/devicetree/bindings/phy/phy-tegra194-p2u.txt
> > new file mode 100644
> > index 000000000000..8b543cba483b
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/phy/phy-tegra194-p2u.txt
> > @@ -0,0 +1,28 @@
> > +NVIDIA Tegra194 P2U binding
> > +
> > +Tegra194 has two PHY bricks namely HSIO (High Speed IO) and NVHS (NVIDIA High
> > +Speed) each interfacing with 12 and 8 P2U instances respectively.
> > +A P2U instance is a glue logic between Synopsys DesignWare Core PCIe IP's PIPE
> > +interface and PHY of HSIO/NVHS bricks. Each P2U instance represents one PCIe
> > +lane.
> > +
> > +Required properties:
> > +- compatible: For Tegra19x, must contain "nvidia,tegra194-p2u".
> > +- reg: Should be the physical address space and length of respective each P2U
> > +       instance.
> > +- reg-names: Must include the entry "ctl".
> 
> -names is pointless when there is only 1.

We've occasionally done this in the past for other types of resources.
When we did it was to preempt having to verbosely describe exactly what
order -names entries need to be in if ever a new entry was required.

For example, if we document only one clock for a module and leave out
the clock-names property, then if ever we need to add another clock, it
means that clock-names must be documented in such a way that the "main"
clock (the one that was always documented) would need to be first in the
list of clock-names, so that it's matching entry in the clocks property
is at index 0, because that's effectively what the ABI is.

I think the same essentially applies to memory regions, though
admittedly I have a hard time seeing us add a second region at any point
in the future.

Thierry

> > +
> > +Required properties for PHY port node:
> > +- #phy-cells: Defined by generic PHY bindings.  Must be 0.
> > +
> > +Refer to phy/phy-bindings.txt for the generic PHY binding properties.
> > +
> > +Example:
> > +
> > +p2u_hsio_0: p2u@...0000 {
> 
> phy@...
> 
> > +	compatible = "nvidia,tegra194-p2u";
> > +	reg = <0x03e10000 0x10000>;
> > +	reg-names = "ctl";
> > +
> > +	#phy-cells = <0>;
> > +};
> > -- 
> > 2.17.1
> > 

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