Re: [PATCH v5 6/6] PCI: dwc: rcar-gen4: Add support for R-Car X5H PCIe4
From: Marek Vasut
Date: Mon Sep 28 2026 - 20:44:31 EST
On 9/29/26 12:24 AM, Bjorn Helgaas wrote:
Hello Bjorn,
The gen5/pcie4 usage is confusing.
I often push back on things like "PCIe Gen4" because it's ambiguous
(does it mean "compliant with base spec r4.0" or "supports 16 GT/s" or
something else), but it's so widely used to mean transfer rate that
it's hard to resist, and the best I can hope for is clarification.
But in "renesas,rcar-gen5-pcie4", I don't know what the 5 and the 4
mean. Maybe "gen5" refers to some internal R-Car thing, and "pcie4"
is something like "PCIe Gen4, i.e., 16 GT/s"?
Gen5 refers to R-Car Gen5 (5th R-Car SoC generation).
PCIe4 refers to the PCIe Gen4 core in the R-Car Gen5 SoC. There is also PCIe
Gen6 core in the same SoC, but that will require a different driver and
different compatible string.
Since none of this shipped in any kernel version yet, would you prefer some
sort of rename ? I can send patches.
Huh. TIL that pcie-rcar-gen4.c refers to the 4th generation R-Car
SoCs
Yes.
(and, I guess the point of this series is to add support for 5th
generation SoCs), not to PCIe Gen4 link speeds.
Correct.
I see that
"renesas,rcar-genX" is all over the place in 'compatible' strings, so
I guess we should follow that precedent.
Yes.
If the "renesas,rcar-gen5" SoC includes both PCIe Gen4 and PCIe Gen6
cores, I suppose everybody refers to them as pcie-gen4 and pcie-gen6,
so the "renesas,rcar-gen5-pcie4" you used is probably the obvious
choice.
Right, and also the least cumbersome compatible string I could come up with.
But maybe we can make commit logs less confusing by saying things
like:
- R-Car Gen4 SoCs S4/V4H/V4M
- R-Car Gen5 SoC X5H
- the R-Car Gen5 SoC PCIe Gen4 core
- the R-Car R8A78000 X5H PCIe Gen4 core, which supports a x8 link at
16 GT/s
Understood, I'll expand future patches to be more explicit about this.
Does that work for you ?
--
Best regards,
Marek Vasut