Re: [PATCH v3 4/9] dt-bindings: PCI: renesas,r9a08g045s33-pcie: Add documentation for the PCIe IP on Renesas RZ/G3S

[Geert Uytterhoeven]

Hi Claudiu,

On Fri, 8 Aug 2025 at 13:44, Claudiu Beznea <claudiu.beznea@xxxxxxxxx> wrote:
> On 09.07.2025 16:43, Krzysztof Kozlowski wrote:
> > On 09/07/2025 15:24, Bjorn Helgaas wrote:
> >> On Wed, Jul 09, 2025 at 08:47:05AM +0200, Krzysztof Kozlowski wrote:
> >>> On 08/07/2025 18:34, Bjorn Helgaas wrote:
> >>>> On Fri, Jul 04, 2025 at 07:14:04PM +0300, Claudiu wrote:
> >>>>> From: Claudiu Beznea <claudiu.beznea.uj@xxxxxxxxxxxxxx>
> >>>>>
> >>>>> The PCIe IP available on the Renesas RZ/G3S complies with the PCI Express
> >>>>> Base Specification 4.0. It is designed for root complex applications and
> >>>>> features a single-lane (x1) implementation. Add documentation for it.
> >>>>
> >>>>> +++ b/Documentation/devicetree/bindings/pci/renesas,r9a08g045s33-pcie.yaml
> >>>>
> >>>> The "r9a08g045s33" in the filename seems oddly specific.  Does it
> >>>> leave room for descendants of the current chip that will inevitably be
> >>>> added in the future?  Most bindings are named with a fairly generic
> >>>> family name, e.g., "fsl,layerscape", "hisilicon,kirin", "intel,
> >>>> keembay", "samsung,exynos", etc.
> >>>>
> >>>
> >>> Bindings should be named by compatible, not in a generic way, so name is
> >>> correct. It can always grow with new compatibles even if name matches
> >>> old one, it's not a problem.
> >>
> >> Ok, thanks!
> >>
> >> I guess that means I'm casting shade on the "r9a08g045s33" compatible.
> >> I suppose it means something to somebody.
> >
> > Well, I hope it matches the name of the SoC, from which the compatible
> > should come :)
>
> The r9a08g45s33 is the part number of a device from the RZ/G3S group. This
> particular device from RZ/G3S group supports PCIe.
>
> In the RZ/G3S group there are more SoC variants (each with its own part
> number). Not all support PCIe. To differentiate b/w PCIe and non-PCIe
> variants it has been chosen to use the full part number here.
>
> The available RZ/G3S part numbers are listed in Table 1.1 Product Lineup at [1]
>
> (The following steps should be followed to access the manual:
> 1/ Click the "User Manual" button
> 2/ Click "Confirm"; this will start downloading an archive
> 3/ Open the downloaded archive
> 4/ Navigate to r01uh1014ej*-rzg3s-users-manual-hardware -> Deliverables
> 5/ Open the file r01uh1014ej*-rzg3s.pdf)
>
> We use a similar compatible scheme in other drivers.
>
> Geert, I may be wrong. Please correct me otherwise, as I don't have the
> full picture of this.
>
> Maybe, the other variant would be to use "renesas,rzg3s-pcie", or maybe a
> more generic one "renesas,rz-pcie" (though I think this last one is too
> generic).

Both would be too generic for the myriad of RZ devices.

AFAIU, the R9A08G045Sxx variants are really the same SoC, with some
hardware modules disabled/nonfunctional.  This is typically handled by:
  1. Using the base part number (r9a08g045) in the compatible value,
  2. Having the device node in the base .dtsi,
  3. Deleting nodes in the variant-specific .dtsi file when needed
     (see e.g. arch/arm64/boot/dts/renesas/r9a09g047{,e[35]7}.dtsi)

Hence as R9A08G045S13, R9A08G045S17, R9A08G045S33, and
R9A08G045S37 all have PCIe, I think it is more appropriate
to use "renesas,r9a08g045-pcie" as the compatible value than
"renesas,r9a08g045s33-pcie".

> Geert, please let us know if you have some suggestions here with regards to
> the compatible. The IP on RZ/G3S is compatible also with the one in RZ/V2H,
> RZ/G3E.

RZ/V2H and RZ/G3E can use "renesas,r9a09g057-pcie" resp.
"renesas,r9a09g047-pcie", with "renesas,r9a08g045-pcie" as a fallback.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds