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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <395343ba-93cc-495c-b5eb-7ee425996465@mailbox.org>
Date: Sun, 25 May 2025 15:33:05 +0200
From: Marek Vasut <marek.vasut@...lbox.org>
To: Geert Uytterhoeven <geert@...ux-m68k.org>
Cc: Rob Herring <robh@...nel.org>,
 Marek Vasut <marek.vasut+renesas@...lbox.org>,
 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 4/23/25 11:38 AM, Geert Uytterhoeven wrote:
> Hi Marek,

Hi,

> On Sun, 13 Apr 2025 at 11:29, Marek Vasut <marek.vasut@...lbox.org> wrote:
>> 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) ?
> 
> I think Rob wants you to add clocks/clock-names for this to
> dtschema/schemas/pci/pci-bus-common.yaml.  Then you can have pcie@M,N
> subnode(s) with num-lanes, clock, and clock-names describing the PCIe
> endpoint(s)?
> 
> git grep "pcie*@[0-9],[0-9]" -- $(git grep -l num-lanes -- Documentation/ )
> 
> Does that make sense?

No, not really. There can be any arbitrary PCIe card plugged into the 
M.2 slot, so how can I predict what exactly will be plugged into the 
slot and describe it in DT up front this way ?

-- 
Best regards,
Marek Vasut