linux-kernel - Re: [PATCH 3/4 v3] PCI: s32g: Add initial PCIe support (RC)

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Message-ID: <aQsmtKsTEmf7e7Sd@ryzen>
Date: Wed, 5 Nov 2025 11:28:04 +0100
From: Niklas Cassel <cassel@...nel.org>
To: Vincent Guittot <vincent.guittot@...aro.org>
Cc: Bjorn Helgaas <helgaas@...nel.org>, chester62515@...il.com,
	mbrugger@...e.com, ghennadi.procopciuc@....nxp.com, s32@....com,
	bhelgaas@...gle.com, jingoohan1@...il.com, lpieralisi@...nel.org,
	kwilczynski@...nel.org, mani@...nel.org, robh@...nel.org,
	krzk+dt@...nel.org, conor+dt@...nel.org, Ionut.Vicovan@....com,
	larisa.grigore@....com, Ghennadi.Procopciuc@....com,
	ciprianmarian.costea@....com, bogdan.hamciuc@....com,
	Frank.li@....com, linux-arm-kernel@...ts.infradead.org,
	linux-pci@...r.kernel.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org, imx@...ts.linux.dev
Subject: Re: [PATCH 3/4 v3] PCI: s32g: Add initial PCIe support (RC)

On Fri, Oct 24, 2025 at 08:50:46AM +0200, Vincent Guittot wrote:
> On Wed, 22 Oct 2025 at 21:04, Bjorn Helgaas <helgaas@...nel.org> wrote:
> > > +     dw_pcie_dbi_ro_wr_en(pci);
> > > +
> > > +     val = dw_pcie_readl_dbi(pci, PCIE_PORT_FORCE);
> > > +     val |= PORT_FORCE_DO_DESKEW_FOR_SRIS;
> > > +     dw_pcie_writel_dbi(pci, PCIE_PORT_FORCE, val);
> > > +
> > > +     /*
> > > +      * Set max payload supported, 256 bytes and
> > > +      * relaxed ordering.
> > > +      */
> > > +     val = dw_pcie_readl_dbi(pci, offset + PCI_EXP_DEVCTL);
> > > +     val &= ~(PCI_EXP_DEVCTL_RELAX_EN |
> > > +              PCI_EXP_DEVCTL_PAYLOAD |
> > > +              PCI_EXP_DEVCTL_READRQ);
> > > +     val |= PCI_EXP_DEVCTL_RELAX_EN |
> > > +            PCI_EXP_DEVCTL_PAYLOAD_256B |
> > > +            PCI_EXP_DEVCTL_READRQ_256B;
> > > +     dw_pcie_writel_dbi(pci, offset + PCI_EXP_DEVCTL, val);
> >
> > MPS and relaxed ordering should be configured by the PCI core.  Is
> > there some s32g-specific restriction about these?
> 
> I will check with the team why they did that

Most likely, the reason is that, the PCI core does not set the MPS to the
maximum supported MPS for the root port.

So without that change, the port will use use 128B instead of 256B.

I assume that you should be able to drop (at least the MPS part) if this
change gets accepted:
https://lore.kernel.org/linux-pci/20251104165125.174168-1-18255117159@163.com/


Kind regards,
Niklas