linux-kernel - Re: [PATCH v2] PCI : Fix pcie_flag_reg in set_pcie_port

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Message-ID: <20241216081048.GE3713119@black.fi.intel.com>
Date: Mon, 16 Dec 2024 10:10:48 +0200
From: Mika Westerberg <mika.westerberg@...ux.intel.com>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: Gowthami Thiagarajan <gthiagarajan@...vell.com>, bhelgaas@...gle.com,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Subject: Re: [PATCH v2] PCI : Fix pcie_flag_reg in set_pcie_port_type

On Fri, Dec 13, 2024 at 12:47:00PM -0600, Bjorn Helgaas wrote:
> [+cc Mika, Andy]
> 
> On Fri, Dec 13, 2024 at 12:32:41PM +0530, Gowthami Thiagarajan wrote:
> > When an invalid PCIe topology is detected, the set_pcie_port_type function 
> > does not set the port type correctly. This issue can occur in 
> > configurations such as:
> > 
> > 	Root Port ---> Downstream Port ---> Root Port
> > 
> > In such cases, the topology is identified as invalid and due to the
> > incorrect port type setting, the extended configuration space of the
> > child device becomes inaccessible.
> 
> >From reading the code, it looks like the underlying problem is
> components that advertise the wrong PCIe Device/Port Type.
> 
> set_pcie_port_type() already detects that incorrect Port Type and
> tries to correct it, but it puts the corrected type in bits [3:0]
> instead of [7:4] where it belongs.
> 
> This looks like a bug from ca78410403dd ("PCI: Get rid of
> dev->has_secondary_link flag").  If so, we should add a Fixes: tag for
> that and possibly a stable tag.

Yeah agree, this is definitely a bug in that commit.

> This looks like a clear bug.  What system tripped over this?  It's
> useful to have bread crumbs like that in case we see other issues
> caused by hardware/firmware defects like this.
> 
> > Signed-off-by: Gowthami Thiagarajan <gthiagarajan@...vell.com>
> > ---
> > v1->v2:
> > 	Updated commit description
> > 
> >  drivers/pci/probe.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> > index 4f68414c3086..263ec21451d9 100644
> > --- a/drivers/pci/probe.c
> > +++ b/drivers/pci/probe.c
> > @@ -1596,7 +1596,7 @@ void set_pcie_port_type(struct pci_dev *pdev)
> >  		if (pcie_downstream_port(parent)) {
> >  			pci_info(pdev, "claims to be downstream port but is acting as upstream port, correcting type\n");
> >  			pdev->pcie_flags_reg &= ~PCI_EXP_FLAGS_TYPE;
> > -			pdev->pcie_flags_reg |= PCI_EXP_TYPE_UPSTREAM;
> > +			pdev->pcie_flags_reg |= PCI_EXP_TYPE_UPSTREAM << 4;
> >  		}
> >  	} else if (type == PCI_EXP_TYPE_UPSTREAM) {
> >  		/*
> > @@ -1607,7 +1607,7 @@ void set_pcie_port_type(struct pci_dev *pdev)
> >  		if (pci_pcie_type(parent) == PCI_EXP_TYPE_UPSTREAM) {
> >  			pci_info(pdev, "claims to be upstream port but is acting as downstream port, correcting type\n");
> >  			pdev->pcie_flags_reg &= ~PCI_EXP_FLAGS_TYPE;
> > -			pdev->pcie_flags_reg |= PCI_EXP_TYPE_DOWNSTREAM;
> > +			pdev->pcie_flags_reg |= PCI_EXP_TYPE_DOWNSTREAM << 4;
> >  		}
> >  	}
> >  }
> > -- 
> > 2.25.1
> >