linux-kernel - Re: [PATCH v5 08/10] misc: rp1: RaspberryPi RP1 misc driver

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Message-ID: <20250109155036.27b82b7e@bootlin.com>
Date: Thu, 9 Jan 2025 15:50:36 +0100
From: Herve Codina <herve.codina@...tlin.com>
To: Andrea della Porta <andrea.porta@...e.com>
Cc: Rob Herring <robh@...nel.org>, Michael Turquette
 <mturquette@...libre.com>, Stephen Boyd <sboyd@...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>, Luca Ceresoli
 <luca.ceresoli@...tlin.com>, Thomas Petazzoni
 <thomas.petazzoni@...tlin.com>, Andrew Lunn <andrew@...n.ch>
Subject: Re: [PATCH v5 08/10] misc: rp1: RaspberryPi RP1 misc driver

Hi Andrea,

On Thu, 9 Jan 2025 15:13:42 +0100
Andrea della Porta <andrea.porta@...e.com> wrote:

> Hi Rob,
> 
> On 15:08 Mon 16 Dec     , Andrea della Porta wrote:
> > Hi Rob,
> > 
> > On 16:48 Tue 10 Dec     , Rob Herring wrote:  
> > > On Mon, Dec 02, 2024 at 12:19:32PM +0100, Andrea della Porta wrote:  
> > > > The RaspberryPi RP1 is a PCI multi function device containing
> > > > peripherals ranging from Ethernet to USB controller, I2C, SPI
> > > > and others.  
> 
> ...
> 
> > > > +#define RP1_INT_ADC_FIFO	52
> > > > +#define RP1_INT_PCIE_OUT	53
> > > > +#define RP1_INT_SPI6		54
> > > > +#define RP1_INT_SPI7		55
> > > > +#define RP1_INT_SPI8		56
> > > > +#define RP1_INT_SYSCFG		58
> > > > +#define RP1_INT_CLOCKS_DEFAULT	59
> > > > +#define RP1_INT_VBUSCTRL	60
> > > > +#define RP1_INT_PROC_MISC	57  
> > > 
> > > Why all these defines which will never be used because they come from 
> > > DT?
> > >  
> > 
> > Right, those defines where originally designed to be included from dts, but
> > previous discussion deemed interrupt numbers to be hardcoded instead of being
> > specified as mnemonics. In the driver source code I just use RP1_INT_END as the
> > number of interrupts but I thought that the specific interrupt numbers should
> > be documented in some way or another. Since no one is currently referencing
> > those defines, would it be better to just turn those in a multiline comment
> > just to describe them in a more compact form?  
> 
> So, here's a couple of proposals about the interrupt defines:
> 
> - since they were banned from devicetree, and are not used anywhere in the code,
>   turn them into a (admittedly long) multiline comment, so they are still at
>   least documented
> 
> - since they were banned from devicetree, and are not use anywhere in the code,
>   just drop them, we don't currently need them after all
> 
> Not sure what's the best way here, anyone can advise?

Maybe in the #interrupt-cells description in the device-tree binding?

In your patch 4, you describe this interrupt controller and you have:
  '#interrupt-cells':
    const: 2
    description:
      Specifies respectively the interrupt number and flags as defined
      in include/dt-bindings/interrupt-controller/irq.h.

In this description, why not add the supported interrupt number values?
    description: |
      Specifies respectively the interrupt number and flags as defined
      in include/dt-bindings/interrupt-controller/irq.h.
      The supported values for the interrupt number are:
        - IO BANK0: 0
        - IO BANK1: 1
...

Or something similar.

This kind of description is already available. For instance:
  https://elixir.bootlin.com/linux/v6.13-rc1/source/Documentation/devicetree/bindings/dma/fsl,imx-sdma.yaml#L64

Does it make sense?

Best regards,
Hervé