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

On Thu, May 07, 2026 at 08:41:23AM +0800, Inochi Amaoto wrote:
> 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.
> > 
> 
> I think it is possible to quirk all the SG2042 products, because the
> typical usage already shows MSI shortage (And this is why SG2044 has
> 512 MSIs). Although it may left some MSIs in the test case, MSI shortage
> is a common issue in a real scenario. And the Sophgo already maintains
> a whitelist to limit the MSI usage of most devices in their vendor
> kernel. So I think it is fine to quirk all the products that use SG2042.
> 

I'm not too sure about quirk. We usually add quirks to workaround the hardware
issues. But what you are seeing is a platform limitation, which is a common
scenario. So adding a cmdline param would help other platforms as well (without
any more code changes).

- Mani

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