Re: [PATCH v5 6/6] PCI: dwc: rcar-gen4: Add support for R-Car X5H PCIe4

[Marek Vasut <marek.vasut@mailbox.org>]

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