linux-kernel - Re: [PATCH v3 01/12] dt-bindings: clock: Add RaspberryPi RP1 clock bindings

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Message-ID: <ZzcxIYKcZ-z6ubrZ@apocalypse>
Date: Fri, 15 Nov 2024 12:31:45 +0100
From: Andrea della Porta <andrea.porta@...e.com>
To: Andrea della Porta <andrea.porta@...e.com>
Cc: Krzysztof Kozlowski <krzk@...nel.org>,
	Michael Turquette <mturquette@...libre.com>,
	Stephen Boyd <sboyd@...nel.org>, Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Florian Fainelli <florian.fainelli@...adcom.com>,
	Broadcom internal kernel review list <bcm-kernel-feedback-list@...adcom.com>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Krzysztof Wilczynski <kw@...ux.com>,
	Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Linus Walleij <linus.walleij@...aro.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>, Bartosz Golaszewski <brgl@...ev.pl>,
	Derek Kiernan <derek.kiernan@....com>,
	Dragan Cvetic <dragan.cvetic@....com>,
	Arnd Bergmann <arnd@...db.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Saravana Kannan <saravanak@...gle.com>, linux-clk@...r.kernel.org,
	devicetree@...r.kernel.org, linux-rpi-kernel@...ts.infradead.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org, linux-gpio@...r.kernel.org,
	Masahiro Yamada <masahiroy@...nel.org>,
	Stefan Wahren <wahrenst@....net>,
	Herve Codina <herve.codina@...tlin.com>,
	Luca Ceresoli <luca.ceresoli@...tlin.com>,
	Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
	Andrew Lunn <andrew@...n.ch>
Subject: Re: [PATCH v3 01/12] dt-bindings: clock: Add RaspberryPi RP1 clock
 bindings

Hi Krzysztof,

On 10:16 Thu 31 Oct     , Andrea della Porta wrote:
> Hi Krzysztof,
> 
> On 08:23 Tue 29 Oct     , Krzysztof Kozlowski wrote:
> > On Mon, Oct 28, 2024 at 03:07:18PM +0100, Andrea della Porta wrote:
> > > Add device tree bindings for the clock generator found in RP1 multi
> > > function device, and relative entries in MAINTAINERS file.
> > > 
> > > Signed-off-by: Andrea della Porta <andrea.porta@...e.com>
> > > ---
> > >  .../clock/raspberrypi,rp1-clocks.yaml         | 62 +++++++++++++++++++
> > >  MAINTAINERS                                   |  6 ++
> > >  .../clock/raspberrypi,rp1-clocks.h            | 61 ++++++++++++++++++
> > >  3 files changed, 129 insertions(+)
> > >  create mode 100644 Documentation/devicetree/bindings/clock/raspberrypi,rp1-clocks.yaml
> > >  create mode 100644 include/dt-bindings/clock/raspberrypi,rp1-clocks.h
> > > 
> > > diff --git a/Documentation/devicetree/bindings/clock/raspberrypi,rp1-clocks.yaml b/Documentation/devicetree/bindings/clock/raspberrypi,rp1-clocks.yaml
> > > new file mode 100644
> > > index 000000000000..a123dd619f8e
> > > --- /dev/null
> > > +++ b/Documentation/devicetree/bindings/clock/raspberrypi,rp1-clocks.yaml
> > > @@ -0,0 +1,62 @@
> > > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > > +%YAML 1.2
> > > +---
> > > +$id: http://devicetree.org/schemas/clock/raspberrypi,rp1-clocks.yaml#
> > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > +
> > > +title: RaspberryPi RP1 clock generator
> > > +
> > > +maintainers:
> > > +  - Andrea della Porta <andrea.porta@...e.com>
> > > +
> > > +description: |
> > > +  The RP1 contains a clock generator designed as three PLLs (CORE, AUDIO,
> > > +  VIDEO), and each PLL output can be programmed though dividers to generate
> > > +  the clocks to drive the sub-peripherals embedded inside the chipset.
> > > +
> > > +  Link to datasheet:
> > > +  https://datasheets.raspberrypi.com/rp1/rp1-peripherals.pdf
> > > +
> > > +properties:
> > > +  compatible:
> > > +    const: raspberrypi,rp1-clocks
> > > +
> > > +  reg:
> > > +    maxItems: 1
> > > +
> > > +  '#clock-cells':
> > > +    description:
> > > +      The index in the assigned-clocks is mapped to the output clock as per
> > > +      definitions in include/dt-bindings/clock/raspberrypi,rp1-clocks.h.
> > 
> > You still describe how current driver matches assigned-clocks to your
> > output clocks. That's not the property of clock-cells and that's not how
> > assigned-clocks work.
> 
> This description is taken by another upstream binding, please see
> Documentation/devicetree/bindings/clock/renesas,5p35023.yaml
> 
> Its purpose is to let the user know how clock-cell number specified
> in assigned-clocks is mapped to the clock provided by this generator.
> Since some of these clocks are shared among peripherals, their frequency
> cannot be set by consumers, so it's the provider itself (i.e. the clock
> device described with this binding) that should take care of them.
> The renesas example has assigned-clocks specified though, please see below.
> 
> > 
> > There are no assigned clocks in your DTS, so this is really irrelevant
> > (or not correct, choose).
> 
> In the first revision of this patchset (please see [1] and following messages)
> I had the assigned-clocks setup in the example while trying to explain their
> purpose, but Conor said those didn't seem to be relevant, hence I dropped them.
> Maybe I had to be more incisive on that.
> So, I'd be inclined to retain the description as it is and reintroduce some
> assigned-clocks in the example as in the renesas one, would it be ok for you?

Since I'm on the verge of producing a new patchset revision, may I kindly ask
some comments on this? Is it ok for you?

Many thanks,
Andrea

> 
> > 
> > 
> > > +    const: 1
> > > +
> > > +  clocks:
> > > +    maxItems: 1
> > > +
> > > +  clock-names:
> > > +    const: xosc
> > 
> > What is the purpose of clock-names if you do not use it? Drop.
> 
> Ack.
> 
> > 
> > > +
> > > +required:
> > > +  - compatible
> > > +  - reg
> > > +  - '#clock-cells'
> > > +  - clocks
> > > +
> > > +additionalProperties: false
> > > +
> > > +examples:
> > > +  - |
> > > +    #include <dt-bindings/clock/raspberrypi,rp1-clocks.h>
> > > +
> > > +    rp1 {
> > > +        #address-cells = <2>;
> > > +        #size-cells = <2>;
> > > +
> > > +        clocks@...0018000 {
> > > +            compatible = "raspberrypi,rp1-clocks";
> > > +            reg = <0xc0 0x40018000 0x0 0x10038>;
> > > +            #clock-cells = <1>;
> > > +            clocks = <&clk_rp1_xosc>;
> > > +            clock-names =  "xosc";
> > 
> > Only one space after '='.
> 
> I will drop the name since the driver will not refer to it via clk_get()
> but will use clk_parent_data::index.
> 
> Many thanks,
> Andrea
> 
> [1] - https://lore.kernel.org/all/20240822-refutable-railroad-a3f111ab1e3f@spud/
> 
> > 
> > Best regards,
> > Krzysztof
> >