linux-kernel - Re: [PATCH] PCI: pcie-rcar: Fix OF node passed to MSI irq domain

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Date:	Mon, 9 Nov 2015 17:11:16 +0100
From:	Thierry Reding <treding@...dia.com>
To:	Phil Edworthy <phil.edworthy@...esas.com>
CC:	Bjorn Helgaas <bhelgaas@...gle.com>,
	Wolfram Sang <wsa@...-dreams.de>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Simon Horman <horms@...ge.net.au>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-sh@...r.kernel.org" <linux-sh@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Ley Foon Tan <lftan@...era.com>,
	Jingoo Han <jg1.han@...sung.com>
Subject: Re: [PATCH] PCI: pcie-rcar: Fix OF node passed to MSI irq domain

On Mon, Nov 09, 2015 at 03:20:24PM +0000, Phil Edworthy wrote:
> cc'ing others (Tegra, Altera, Designware) who may have the same bug
> 
> On 03 November 2015 09:28, Phil Edworthy wrote:
> > The OF node passed to irq_domain_add_linear() should be a
> > pointer to interrupt controller's device tree node, or NULL,
> > but not the PCI controller's node.
> > 
> > This fixes an oops in msi_domain_alloc_irqs() when it tries
> > to call msi_check().
> > 
> > Signed-off-by: Phil Edworthy <phil.edworthy@...esas.com>
> > ---
> >  drivers/pci/host/pcie-rcar.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/pci/host/pcie-rcar.c b/drivers/pci/host/pcie-rcar.c
> > index 2377bf0..c6fa562 100644
> > --- a/drivers/pci/host/pcie-rcar.c
> > +++ b/drivers/pci/host/pcie-rcar.c
> > @@ -709,7 +709,7 @@ static int rcar_pcie_enable_msi(struct rcar_pcie *pcie)
> >  	msi->chip.setup_irq = rcar_msi_setup_irq;
> >  	msi->chip.teardown_irq = rcar_msi_teardown_irq;
> > 
> > -	msi->domain = irq_domain_add_linear(pcie->dev->of_node,
> > INT_PCI_MSI_NR,
> > +	msi->domain = irq_domain_add_linear(NULL, INT_PCI_MSI_NR,
> >  					    &msi_domain_ops, &msi->chip);
> >  	if (!msi->domain) {
> >  		dev_err(&pdev->dev, "failed to create IRQ domain\n");

On Tegra the PCI controller is in fact the interrupt controller for
MSIs. And looking at the code here it seems like the same would apply to
RCAR.

I'm also slightly confused as to why this would cause ->msi_check() to
fail. The default implementation (msi_domain_ops_check()) doesn't do
anything.

Also, how is passing in NULL instead of a valid struct device_node *
going to prevent an oops? Perhaps this is one of those reference count
imbalance bugs that have recently been showing up?

Thierry

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