linux-kernel - Re: [PATCH] PCI: MSI: Only use the generic MSI layer when domain is hierarchical

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Date:	Fri, 4 Dec 2015 11:46:21 -0600
From:	Bjorn Helgaas <helgaas@...nel.org>
To:	Marc Zyngier <marc.zyngier@....com>
Cc:	Phil Edworthy <phil.edworthy@...esas.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jiang Liu <jiang.liu@...ux.intel.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Wolfram Sang <wsa@...-dreams.de>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>
Subject: Re: [PATCH] PCI: MSI: Only use the generic MSI layer when domain is
 hierarchical

On Fri, Dec 04, 2015 at 05:07:47PM +0000, Marc Zyngier wrote:
> Hi Bjorn,
> 
> On 04/12/15 16:17, Bjorn Helgaas wrote:
> > On Fri, Dec 04, 2015 at 08:13:50AM +0000, Marc Zyngier wrote:
> >> On Thu, 3 Dec 2015 18:27:59 -0600
> >> Bjorn Helgaas <helgaas@...nel.org> wrote:
> >>
> >>> On Mon, Nov 30, 2015 at 10:25:34AM +0000, Phil Edworthy wrote:
> >>>> Cc'd linux-pci ml
> >>>>
> >>>> On 23 November 2015 14:27, Marc Zyngier wrote:
> >>>>
> >>>> Since d8a1cb757550 ("PCI/MSI: Let pci_msi_get_domain use struct
> >>>> device::msi_domain"), we use the MSI domain associated to the PCI device.
> >>>>
> >>>> But finding a MSI domain doesn't mean that the domain is implemented
> >>>> using the generic MSI domain API, and a number of MSI controllers
> >>>> are still using the arch_setup_msi_irq/arch_teardown_msi_irqs.
> >>>>
> >>>> In order to avoid a firework on these systems, check that the domain
> >>>> we just obtained is hierarchical. If not, don't use the generic MSI
> >>>> stuff and stick with the old one. Not pretty, but reliable.
> >>>>
> >>>> Another insentive to rework those drivers and phase out this API.
> >>>>
> >>>> Reported-by: Phil Edworthy <phil.edworthy@...esas.com>
> >>>> Tested-by: Phil Edworthy <phil.edworthy@...esas.com>
> >>>> Signed-off-by: Marc Zyngier <marc.zyngier@....com>
> >>>
> >>> Thanks, I applied this with Thomas' ack to pci/msi for v4.5.
> >>>
> >>> It looks like d8a1cb757550 appeared in v4.3.  Is this a fix for that
> >>> commit?  Does this need to be backported via a stable tag?
> >>
> >> Hi Bjorn,
> >>
> >> I think this really deserves to be queued as an immediate fix for 4.4
> >> rather than 4.5, as some systems in mainline are affected by this bug:
> >>
> >> http://www.spinics.net/lists/arm-kernel/msg465792.html
> >>
> >> It would also deserve a stable tag for 4.3.
> > 
> > OK, I can do that.  It would save me a lot of time to get a hint when
> > this is the case.  I couldn't tell if this issue happened on mainline
> > or with some still out-of-tree patches.  I'd also like to know what
> > machines are affected.
> 
> Sorry, I should have been more clear. At the moment, I've had reports of
> at least RCar, Tegra and Armada 370 being affected. Anything using the
> Designware driver will probably also fall over.
> 
> > I did look at d8a1cb757550, and the connection between that and this
> > patch is not completely obvious; would you regard this as a fix to
> > d8a1cb757550?  Should this patch be backported to every kernel that
> > includes d8a1cb757550?  Or is this more closely tied to some other
> > change?
> 
> d8a1cb757550 is indeed the source of the problem: we assumes that
> finding a domain identified by a given device is enough to decide that
> we're using the generic MSI layer. Unfortunately, this is not the case,
> and a number of ARM drivers are actually registering their own domain
> the same way, without using the generic MSI layer. I didn't spot this on
> arm64, as all my platforms are using this layer.
> 
> So it seems better to merge this in 4.4, with a backport to 4.3 (which
> is the first kernel to contain this commit).

Thanks, Marc!  I moved this to for-linus for v4.4, added info about
the machines, and added a stable tag for v4.3.

Bjorn
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