linux-kernel - Re: [PATCH v2 3/3] arm64: dts: renesas: r8a779g3: Describe split PCIe clock on V4H Sparrow Hawk

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Message-ID: <CAMuHMdWEmGk0iE0vroGRWOwsK3+EFpbqzO-OH3aVDQTud3wVtQ@mail.gmail.com>
Date: Thu, 5 Jun 2025 09:33:08 +0200
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc: Marek Vasut <marek.vasut+renesas@...lbox.org>, linux-arm-kernel@...ts.infradead.org, 
	Bartosz Golaszewski <brgl@...ev.pl>, Bjorn Helgaas <bhelgaas@...gle.com>, Conor Dooley <conor+dt@...nel.org>, 
	Geert Uytterhoeven <geert+renesas@...der.be>, 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 v2 3/3] arm64: dts: renesas: r8a779g3: Describe split PCIe
 clock on V4H Sparrow Hawk

Hi Mani,

On Wed, 4 Jun 2025 at 19:31, Manivannan Sadhasivam
<manivannan.sadhasivam@...aro.org> wrote:
> On Wed, Jun 04, 2025 at 11:24:17AM +0200, Geert Uytterhoeven wrote:
> > On Sat, 31 May 2025 at 00:55, Marek Vasut
> > <marek.vasut+renesas@...lbox.org> wrote:
> > > The V4H Sparrow Hawk board supplies PCIe controller input clock and PCIe
> > > bus clock from separate outputs of Renesas 9FGV0441 clock generator chip.
> > > Describe this split bus configuration in the board DT. The topology looks
> > > as follows:
> > >
> > >  ____________                    _____________
> > > | 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<|
> > > '------------'
> > >
> > > Signed-off-by: Marek Vasut <marek.vasut+renesas@...lbox.org>
> >
> > Thanks for your patch!
> >
> > > V2: Use pciec0_rp/pciec1_rp phandles to refer to root port moved to core r8a779g0.dtsi
> >
> > Reviewed-by: Geert Uytterhoeven <geert+renesas@...der.be>
> >
> > I understand this has a hard dependency on [PATCH v2 1/3] (and on
> > enabling CONFIG_PCI_PWRCTRL_SLOT), so I cannot apply this before that
> > patch is upstream?
>
> TBH, this patch is describing the binding properly. So even though the driver
> change is necessary to make the device functional, I don't see it as a hard
> dependency. But since people care about functionality, if both driver and DTS
> changes go into the same release, it should be fine IMO.

Applying the DTS change without the driver change would introduce a
regression in my tree.  While the regression would be fixed in linux-next,
it would still hurt bisectability.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds