linux-kernel - Re: [PATCH v11] PCI: Xilinx-NWL-PCIe: Added support for Xilinx NWL PCIe Host Controller

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Message-ID: <566A9852.7060109@arm.com>
Date:	Fri, 11 Dec 2015 09:33:06 +0000
From:	Marc Zyngier <marc.zyngier@....com>
To:	Bjorn Helgaas <helgaas@...nel.org>,
	Bharat Kumar Gogada <bharat.kumar.gogada@...inx.com>
CC:	"robh+dt@...nel.org" <robh+dt@...nel.org>,
	"pawel.moll@....com" <pawel.moll@....com>,
	"mark.rutland@....com" <mark.rutland@....com>,
	"ijc+devicetree@...lion.org.uk" <ijc+devicetree@...lion.org.uk>,
	"galak@...eaurora.org" <galak@...eaurora.org>,
	Michal Simek <michals@...inx.com>,
	Soren Brinkmann <sorenb@...inx.com>,
	"bhelgaas@...gle.com" <bhelgaas@...gle.com>,
	"arnd@...db.de" <arnd@...db.de>,
	"tinamdar@....com" <tinamdar@....com>,
	"treding@...dia.com" <treding@...dia.com>,
	"rjui@...adcom.com" <rjui@...adcom.com>,
	"Minghuan.Lian@...escale.com" <Minghuan.Lian@...escale.com>,
	"m-karicheri2@...com" <m-karicheri2@...com>,
	"hauke@...ke-m.de" <hauke@...ke-m.de>,
	"dhdang@....com" <dhdang@....com>,
	"sbranden@...adcom.com" <sbranden@...adcom.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	Ravikiran Gummaluri <rgummal@...inx.com>,
	Paul Burton <paul.burton@...tec.com>,
	Thierry Reding <thierry.reding@...il.com>,
	Stephen Warren <swarren@...dotorg.org>,
	Alexandre Courbot <gnurou@...il.com>
Subject: Re: [PATCH v11] PCI: Xilinx-NWL-PCIe: Added support for Xilinx NWL
 PCIe Host Controller

On 10/12/15 20:18, Bjorn Helgaas wrote:
> [+cc Marc for irq_dispose_mapping() question]

>>>> +		}
>>>> +	} while (status);
>>>> +
>>>> +	return retval;
>>>>
>>>> +	for (i = 0; i < 4; i++) {
>>>> +		irq = irq_find_mapping(pcie->legacy_irq_domain, i + 1);
>>>> +		if (irq > 0)
>>>> +			irq_dispose_mapping(irq);
>>>> +	}
>>>> +	if (pcie->legacy_irq_domain)
>>>> +		irq_domain_remove(pcie->legacy_irq_domain);
>>>
>>> Something seems wrong here.  I don't know when irq_dispose_mapping() is
>>> required, but it's not used consistently in drivers/pci, and it should be.
>>> Currently, only pci-tegra.c, pcie-xilinx.c, and this new driver use it.  Tegra uses
>>> it only for MSIs, and Xilinx seems to use it for both MSIs and INTx.  What's
>>> right?
>> Its not related to MSI or INTx, its related to domain, for freeing irq descriptor associated with irq.
> 
> So are you saying that other drivers in drivers/pci/host should be
> using irq_dispose_mapping(), but they aren't?
> 
> Marc, can you chime in here?

This indeed looks like be a bug in most drivers. Having a mapping left
when freeing the domain has a couple of side effects:
- We leak virtual interrupt numbers
- If the domain is backed by a radix tree, we leak the tree as well (but
irq_domain_remove will shout if that's the case).

So I think using irq_dispose_mapping is the right thing to do, and that
we should fix the other drivers (and maybe provide a convenient helper
to that effect).

I'll try to come up with something.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...
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