[PATCH 2/2] PCI: Add quirk to disable PCIe port services on Sophgo SG2042

[Manivannan Sadhasivam]

On Sun, May 03, 2026 at 10:52:06AM +0200, Lukas Wunner wrote:
> On Sun, May 03, 2026 at 03:10:58PM +0800, Icenowy Zheng wrote:
> > It's used in multiple products, but only one of them (EVBv1, which is
> > just an early EVB available for a few people including me) lacks an
> > onboard switch, because SG2042 is short on on-chip peripherals. All
> > other devices (including two mainlined ones, EVBv2 and Milk-V Pioneer,
> > and unmainlined dual socket rack servers; Milk-V Pioneer should be the
> > most popular device because it was on shelf) have an onboard switch to
> > mitigate the lack of on-chip peripherals in SG2042.
> 
> Who knows, maybe someone will design a product which doesn't attach
> a PCIe switch to the SoC, maybe the lack of peripherals isn't a
> problem for them.
> 
> It seems reasonable to accommodate such non-switch use cases as well,
> so I think you definitely do not want to quirk all products using that
> SoC but only those that need it, regardless whether it's the majority.
> 
> > > My point is, you want to constrain this to a specific product, not to
> > > the SoC.  Can you maybe solve this by not specifying interrupts in
> > > the devicetree for the PCIe switch?
> > 
> > The PCIe switches are not described in the device tree at all, because
> > they're all just discoverable; can we describe them in the DT and
> > redirect their interrupts to void?
> 
> Yes, somebody did a writeup how to represent switches and endpoints
> in the devicetree:
> 
> https://farlepet.github.io/linux/2024/02/20/using-linux-device-tree-with-pcie-devices.html
> 

I wouldn't recommend going this far... We do have some switches described in DT,
but they have some resource requirements like regulator, i2c...

> And then I would try providing an empty "interrupts" property for
> those switch ports for which you want to avoid port services being
> instantiated.
> 

There is no 'interrupts' property in DT binding for PCI bridge nodes. There is
'interrupt-map', but that's used for mapping INTx with platform interrupt
controller.

Moreover, DT should just describe the hardware topology/resource, not
platform constraints.

I'd recommend introducing a new cmdline param to the portdrv driver to disable
using MSIs for services. But the platform limitation would hit one way or the
other if one of the endpoints consume all MSIs...

- Mani

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