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

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Message-ID: <40c400ab-8770-4595-9a4c-004e6157c348@mailbox.org>
Date: Sun, 13 Apr 2025 11:28:54 +0200
From: Marek Vasut <marek.vasut@...lbox.org>
To: Rob Herring <robh@...nel.org>,
 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>,
 Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
 Neil Armstrong <neil.armstrong@...aro.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 4/10/25 10:48 PM, Rob Herring wrote:
> 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:
>>
>>   ____________                    _____________
>> | 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.
> 
> Pretty sure that PMC is "power management controller" given it talks
> about low power states.
> 
> 
>>
>> 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 ?
> 
> Based on the diagram, this has nothing to do with the specific
> controller. It should also probably a root port property, not host
> bridge.
How would you suggest I describe the clock which supply the PCIe bus 
clock lane (CLK DIF1 in the diagram) , which have to be enabled together 
with clock which supply the PCIe controller input clock lane (CLK DIF0) ?