linux-kernel - Re: [PATCH v3 1/3] PCI/pwrctrl: Add optional slot clock to pwrctrl driver for PCI slots

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Message-ID: <20250613220104.GA986309@bhelgaas>
Date: Fri, 13 Jun 2025 17:01:04 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Geert Uytterhoeven <geert@...ux-m68k.org>
Cc: Marek Vasut <marek.vasut+renesas@...lbox.org>,
	Bartosz Golaszewski <brgl@...ev.pl>,
	linux-arm-kernel@...ts.infradead.org,
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>,
	Anand Moon <linux.amoon@...il.com>,
	Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Conor Dooley <conor+dt@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Magnus Damm <magnus.damm@...il.com>, 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 v3 1/3] PCI/pwrctrl: Add optional slot clock to pwrctrl
 driver for PCI slots

On Thu, Jun 12, 2025 at 03:16:45PM +0200, Geert Uytterhoeven wrote:
> On Sat, 7 Jun 2025 at 21:46, Marek Vasut
> <marek.vasut+renesas@...lbox.org> wrote:
> > Add the ability to enable optional slot clock into the pwrctrl driver.
> > This is used to enable slot clock in split-clock topologies, where the
> > PCIe host/controller supply and PCIe slot supply are not provided by
> > the same clock. The PCIe host/controller clock should be described in
> > the controller node as the controller clock, while the slot clock should
> > be described in controller bridge/slot subnode.
> >
> > Example DT snippet:
> > &pcicontroller {
> >     clocks = <&clk_dif 0>;             /* PCIe controller clock */
> >
> >     pci@0,0 {
> >         #address-cells = <3>;
> >         #size-cells = <2>;
> >         reg = <0x0 0x0 0x0 0x0 0x0>;
> >         compatible = "pciclass,0604";
> >         device_type = "pci";
> >         clocks = <&clk_dif 1>;         /* PCIe slot clock */
> >         vpcie3v3-supply = <&reg_3p3v>;
> >         ranges;
> >     };
> > };
> >
> > Example clock topology:
> >  ____________                    ____________
> > |  PCIe host |                  | PCIe slot  |
> > |            |                  |            |
> > |    PCIe RX<|==================|>PCIe TX    |
> > |    PCIe TX<|==================|>PCIe RX    |
> > |            |                  |            |
> > |   PCIe CLK<|======..  ..======|>PCIe CLK   |
> > '------------'      ||  ||      '------------'
> >                     ||  ||
> >  ____________       ||  ||
> > |  9FGV0441  |      ||  ||
> > |            |      ||  ||
> > |   CLK DIF0<|======''  ||
> > |   CLK DIF1<|==========''
> > |   CLK DIF2<|
> > |   CLK DIF3<|
> > '------------'
> >
> > Acked-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> > Reviewed-by: Anand Moon <linux.amoon@...il.com>
> > Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> > Signed-off-by: Marek Vasut <marek.vasut+renesas@...lbox.org>
> 
> Reviewed-by: Geert Uytterhoeven <geert+renesas@...der.be>
> 
> Bartosz: Any chance you can apply this patch to an immutable branch,
> so I can merge that before taking the other two patches?
> The alternative is to postpone the DTS patches for one cycle.

I applied this patch only to pci/pwrctrl for v6.17 and made a note
that the commit should be immutable:

  66db1d3cbdb0 ("PCI/pwrctrl: Add optional slot clock for PCI slots")

We will likely add other pwrctrl patches to this branch during this
cycle; I assume that will be OK as long as 66db1d3cbdb0 remains
untouched, right?

Bjorn