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

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Date:	Mon, 9 Nov 2015 17:24:06 +0000
From:	Phil Edworthy <phil.edworthy@...esas.com>
To:	Thierry Reding <treding@...dia.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

Hi Thierry,

On 09 November 2015 16:11, Thierry wrote:
> 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.
Yes you are correct here. 

> 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?
On arm64 (previously I didn't realise this just affects arm64, not arm),
the changes in commit f075915ac0b11 ("PCI/MSI: Drop domain field from
msi_controller") and d8a1cb757550 ("PCI/MSI: Let pci_msi_get_domain use
struct device::msi_domain") return an uninitialized msi domain that leads
to the oops. It appears that these changes assume that msi interrupt
controller is separate from the PCI controller.

Phil
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