linux-kernel - Re: [PATCH v2 1/2] PCI: Initialize RCB from pci_configure

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Message-ID: <20260122102257.GA1239174@bhelgaas>
Date: Thu, 22 Jan 2026 04:22:57 -0600
From: Bjorn Helgaas <helgaas@...nel.org>
To: Haakon Bugge <haakon.bugge@...cle.com>
Cc: Bjorn Helgaas <bhelgaas@...gle.com>,
	Johannes Thumshirn <morbidrsa@...il.com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>
Subject: Re: [PATCH v2 1/2] PCI: Initialize RCB from pci_configure_device

On Thu, Jan 22, 2026 at 09:42:46AM +0000, Haakon Bugge wrote:
> > On Wed, Jan 21, 2026 at 12:35:40PM +0100, Håkon Bugge wrote:
> > [snip]
> 
> > RCB isn't meaningful for switches, so we'll read their LNKCTL
> > unnecessarily.  I propose something like this, which also clears RCB
> > if it's set when it shouldn't be (I think this would indicate a
> > firmware defect):
> > 
> >        /*
> >         * Per PCIe r7.0, sec 7.5.3.7, RCB is only meaningful in Root Ports
> >         * (where it is read-only), Endpoints, and Bridges.  It may only be
> >         * set for Endpoints and Bridges if it is set in the Root Port.
> >         */
> >        if (!pci_is_pcie(dev) ||
> >            pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT ||
> >            pci_pcie_type(dev) == PCI_EXP_TYPE_UPSTREAM ||
> >            pci_pcie_type(dev) == PCI_EXP_TYPE_DOWNSTREAM ||
> >            dev->is_virtfn)
> 
> I see that sec 1.3.2 defines "Endpoints are classified as either
> legacy, PCI Express, or Root Complex Integrated Endpoints (RCiEPs)."
> But, shouldn't we also exclude Root Complex Event Collectors
> (PCI_EXP_TYPE_RC_EC)?

Yes, probably so.