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

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Message-ID: <2ny7jhcp2g5ixo75donutncxnjdawzev3mw7cytvhbk6szl3ue@vixax5lwpycw>
Date: Sat, 10 May 2025 01:07:27 +0530
From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To: Marek Vasut <marek.vasut+renesas@...lbox.org>
Cc: linux-arm-kernel@...ts.infradead.org, 
	Niklas Söderlund <niklas.soderlund+renesas@...natech.se>, Krzysztof Wilczyński <kw@...ux.com>, 
	Rafał Miłecki <rafal@...ecki.pl>, Aradhya Bhatia <a-bhatia1@...com>, 
	Bjorn Helgaas <bhelgaas@...gle.com>, Conor Dooley <conor+dt@...nel.org>, 
	Geert Uytterhoeven <geert+renesas@...der.be>, Heiko Stuebner <heiko@...ech.de>, 
	Junhao Xie <bigfoot@...ssfun.cn>, Kever Yang <kever.yang@...k-chips.com>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>, 
	Lorenzo Pieralisi <lpieralisi@...nel.org>, Magnus Damm <magnus.damm@...il.com>, 
	Neil Armstrong <neil.armstrong@...aro.org>, Rob Herring <robh@...nel.org>, 
	Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>, devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-pci@...r.kernel.org, linux-renesas-soc@...r.kernel.org
Subject: Re: [PATCH v2 1/4] dt-bindings: PCI: rcar-gen4-pci-host: Document
 optional aux clock

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@...natech.se>
> Signed-off-by: Marek Vasut <marek.vasut+renesas@...lbox.org>
> ---
> NOTE: Shall we patch Documentation/devicetree/bindings/pci/snps,dw-pcie-common.yaml
>       instead and add 'bus' clock outright ?
> ---
> Cc: "Krzysztof Wilczyński" <kw@...ux.com>
> Cc: "Rafał Miłecki" <rafal@...ecki.pl>
> Cc: Aradhya Bhatia <a-bhatia1@...com>
> Cc: Bjorn Helgaas <bhelgaas@...gle.com>
> Cc: Conor Dooley <conor+dt@...nel.org>
> Cc: Geert Uytterhoeven <geert+renesas@...der.be>
> Cc: Heiko Stuebner <heiko@...ech.de>
> Cc: Junhao Xie <bigfoot@...ssfun.cn>
> Cc: Kever Yang <kever.yang@...k-chips.com>
> Cc: Krzysztof Kozlowski <krzk+dt@...nel.org>
> Cc: Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>
> Cc: Lorenzo Pieralisi <lpieralisi@...nel.org>
> Cc: Magnus Damm <magnus.damm@...il.com>
> Cc: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> Cc: Neil Armstrong <neil.armstrong@...aro.org>
> Cc: Rob Herring <robh@...nel.org>
> Cc: Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>
> Cc: devicetree@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> Cc: linux-pci@...r.kernel.org
> Cc: linux-renesas-soc@...r.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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