[PATCH v2 1/4] dt-bindings: PCI: rcar-gen4-pci-host: Document optional aux clock

[Manivannan Sadhasivam]

On Sun, Apr 06, 2025 at 04:45:21PM +0200, Marek Vasut wrote:
> Document 'aux' clock which are used to supply the PCIe bus. This
> is useful in case of a hardware setup, where the PCIe controller
> input clock and the PCIe bus clock are supplied from the same
> clock synthesiser, but from different differential clock outputs:

How different is this clock from the 'reference clock'? I'm not sure what you
mean by 'PCIe bus clock' here. AFAIK, endpoint only takes the reference clock
and the binding already has 'ref' clock for that purpose. So I don't understand
how this new clock is connected to the endpoint device.

- Mani

> 
>  ____________                    _____________
> | R-Car PCIe |                  | PCIe device |
> |            |                  |             |
> |    PCIe RX<|==================|>PCIe TX     |
> |    PCIe TX<|==================|>PCIe RX     |
> |            |                  |             |
> |   PCIe CLK<|======..  ..======|>PCIe CLK    |
> '------------'      ||  ||      '-------------'
>                     ||  ||
>  ____________       ||  ||
> |  9FGV0441  |      ||  ||
> |            |      ||  ||
> |   CLK DIF0<|======''  ||
> |   CLK DIF1<|==========''
> |   CLK DIF2<|
> |   CLK DIF3<|
> '------------'
> 
> The clock are named 'aux' because those are one of the clock listed in
> Documentation/devicetree/bindings/pci/snps,dw-pcie-common.yaml which
> fit closest to the PCIe bus clock. According to that binding document,
> the 'aux' clock describe clock which supply the PMC domain, which is
> likely PCIe Mezzanine Card domain.
> 
> Tested-by: Niklas Söderlund <niklas.soderlund+renesas at ragnatech.se>
> Signed-off-by: Marek Vasut <marek.vasut+renesas at mailbox.org>
> ---
> NOTE: Shall we patch Documentation/devicetree/bindings/pci/snps,dw-pcie-common.yaml
>       instead and add 'bus' clock outright ?
> ---
> Cc: "Krzysztof Wilczyński" <kw at linux.com>
> Cc: "Rafał Miłecki" <rafal at milecki.pl>
> Cc: Aradhya Bhatia <a-bhatia1 at ti.com>
> Cc: Bjorn Helgaas <bhelgaas at google.com>
> Cc: Conor Dooley <conor+dt at kernel.org>
> Cc: Geert Uytterhoeven <geert+renesas at glider.be>
> Cc: Heiko Stuebner <heiko at sntech.de>
> Cc: Junhao Xie <bigfoot at classfun.cn>
> Cc: Kever Yang <kever.yang at rock-chips.com>
> Cc: Krzysztof Kozlowski <krzk+dt at kernel.org>
> Cc: Kuninori Morimoto <kuninori.morimoto.gx at renesas.com>
> Cc: Lorenzo Pieralisi <lpieralisi at kernel.org>
> Cc: Magnus Damm <magnus.damm at gmail.com>
> Cc: Manivannan Sadhasivam <manivannan.sadhasivam at linaro.org>
> Cc: Neil Armstrong <neil.armstrong at linaro.org>
> Cc: Rob Herring <robh at kernel.org>
> Cc: Yoshihiro Shimoda <yoshihiro.shimoda.uh at renesas.com>
> Cc: devicetree at vger.kernel.org
> Cc: linux-kernel at vger.kernel.org
> Cc: linux-pci at vger.kernel.org
> Cc: linux-renesas-soc at vger.kernel.org
> ---
> V2: - Add TB from Niklas
>     - Document minItems in clock-names
> ---
>  .../devicetree/bindings/pci/rcar-gen4-pci-host.yaml      | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/Documentation/devicetree/bindings/pci/rcar-gen4-pci-host.yaml b/Documentation/devicetree/bindings/pci/rcar-gen4-pci-host.yaml
> index bb3f843c59d91..528b916fdb99b 100644
> --- a/Documentation/devicetree/bindings/pci/rcar-gen4-pci-host.yaml
> +++ b/Documentation/devicetree/bindings/pci/rcar-gen4-pci-host.yaml
> @@ -46,12 +46,15 @@ properties:
>        - const: app
>  
>    clocks:
> -    maxItems: 2
> +    minItems: 2
> +    maxItems: 3
>  
>    clock-names:
> +    minItems: 2
>      items:
>        - const: core
>        - const: ref
> +      - const: aux
>  
>    power-domains:
>      maxItems: 1
> @@ -105,8 +108,8 @@ examples:
>                           <GIC_SPI 418 IRQ_TYPE_LEVEL_HIGH>,
>                           <GIC_SPI 422 IRQ_TYPE_LEVEL_HIGH>;
>              interrupt-names = "msi", "dma", "sft_ce", "app";
> -            clocks = <&cpg CPG_MOD 624>, <&pcie0_clkref>;
> -            clock-names = "core", "ref";
> +            clocks = <&cpg CPG_MOD 624>, <&pcie0_clkref>, <&pcie0_clkgen>;
> +            clock-names = "core", "ref", "aux";
>              power-domains = <&sysc R8A779F0_PD_ALWAYS_ON>;
>              resets = <&cpg 624>;
>              reset-names = "pwr";
> -- 
> 2.47.2
> 

-- 
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