linux-kernel - Re: [PATCH 03/15] PCI: mvebu: Check that PCI bridge specified in DT has function number zero

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Date:   Fri, 7 Jan 2022 19:18:19 +0100
From:   Pali Rohár <pali@...nel.org>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Marek Behún <kabel@...nel.org>,
        linux-pci@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 03/15] PCI: mvebu: Check that PCI bridge specified in DT
 has function number zero

On Friday 07 January 2022 12:15:12 Bjorn Helgaas wrote:
> On Thu, Nov 25, 2021 at 01:45:53PM +0100, Pali Rohár wrote:
> > Driver cannot handle PCI bridges at non-zero function address. So add
> > appropriate check. Currently all in-tree kernel DTS files set PCI bridge
> > function to zero.
> 
> Why can the driver not handle bridges at non-zero function addresses?
> The PCI spec allows that, doesn't it?  Is this a hardware limitation?

It is software / kernel limitation.

Because this bridge is virtual, emulated by pci-bridge-emul.c driver and
this driver can emulate only single function PCI-to-PCI bridge device.

> > Signed-off-by: Pali Rohár <pali@...nel.org>
> > Cc: stable@...r.kernel.org
> > ---
> >  drivers/pci/controller/pci-mvebu.c | 5 +++++
> >  1 file changed, 5 insertions(+)
> > 
> > diff --git a/drivers/pci/controller/pci-mvebu.c b/drivers/pci/controller/pci-mvebu.c
> > index 6197f7e7c317..08274132cdfb 100644
> > --- a/drivers/pci/controller/pci-mvebu.c
> > +++ b/drivers/pci/controller/pci-mvebu.c
> > @@ -864,6 +864,11 @@ static int mvebu_pcie_parse_port(struct mvebu_pcie *pcie,
> >  	port->devfn = of_pci_get_devfn(child);
> >  	if (port->devfn < 0)
> >  		goto skip;
> > +	if (PCI_FUNC(port->devfn) != 0) {
> > +		dev_err(dev, "%s: invalid function number, must be zero\n",
> > +			port->name);
> > +		goto skip;
> > +	}
> >  
> >  	ret = mvebu_get_tgt_attr(dev->of_node, port->devfn, IORESOURCE_MEM,
> >  				 &port->mem_target, &port->mem_attr);
> > -- 
> > 2.20.1
> >