Re: [PATCH] dt-bindings: timer: renesas,tmu: Document input capture interrupt

On Mon, Jan 15, 2024 at 05:48:18PM +0100, Geert Uytterhoeven wrote:
> Hi Conor,
> 
> On Mon, Jan 15, 2024 at 5:13 PM Conor Dooley <[email protected]> wrote:
> > On Mon, Jan 15, 2024 at 02:45:39PM +0100, Geert Uytterhoeven wrote:
> > > Some Timer Unit (TMU) instances with 3 channels support a fourth
> > > interrupt: an input capture interrupt for the third channel.
> > >
> > > While at it, document the meaning of the four interrupts, and add
> > > "interrupt-names" for clarity.
> > >
> > > Update the example to match reality.
> > >
> > > Inspired by a patch by Yoshinori Sato for SH.
> > >
> > > Signed-off-by: Geert Uytterhoeven <[email protected]>
> 
> > > --- a/Documentation/devicetree/bindings/timer/renesas,tmu.yaml
> > > +++ b/Documentation/devicetree/bindings/timer/renesas,tmu.yaml
> > > @@ -46,7 +46,19 @@ properties:
> > >
> > >    interrupts:
> > >      minItems: 2
> > > -    maxItems: 3
> > > +    items:
> > > +      - description: Underflow interrupt 0
> > > +      - description: Underflow interrupt 1
> > > +      - description: Underflow interrupt 2
> > > +      - description: Input capture interrupt 2
> >
> > Seeing "input capture interrupt 2" makes me wonder, are there two (or
> > more!) other input capture interrupts that are still out there,
> > undocumented, and looking for a home?

Maybe writing this as

      - description: Underflow interrupt, channel 0
      - description: Underflow interrupt, channel 1
      - description: Underflow interrupt, channel 2
      - description: Input capture interrupt, channel 2

would make it clearer ?

I'm also wondering if we really need to add interrupt-names. Drivers
can't depend on the names due to backward compatibility, what benefit
does it bring to add them to the bindings ?

> SoCs can have multiple TMU instances.
> Each TMU instance has 2 or 3 timer channels.
> Each timer channel has an underflow interrupt.
> Only the third channel may have an optional input capture interrupt
> (which is not supported yet by the Linux driver).
> Hence each instance can have 2, 3, or 4 interrupts.
> 
> See "RZ/G Series, 2nd Generation User's Manual: Hardware"[1],
> Section 69 ("Timer Unit (TMU)":
>   - Figure 69.2: Block Diagram of TMU,
>   - Section 69: Interrupt
> 
> Note that the documentation uses a monotonic increasing numbering
> of the channels, across all instances.
> 
> [1] https://www.renesas.com/us/en/products/microcontrollers-microprocessors/rz-mpus/rzg2h-ultra-high-performance-microprocessors-quad-core-arm-cortex-a57-and-quad-core-arm-cortex-a53-cpus-3d

-- 
Regards,

Laurent Pinchart