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From: Lucas Stach <l.stach@pengutronix.de>
To: Gustavo Pimentel <gustavo.pimentel@synopsys.com>,
	Marc Zyngier <marc.zyngier@arm.com>
Cc: Bjorn Helgaas <helgaas@kernel.org>,
	Jingoo Han <jingoohan1@gmail.com>,
	Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
	"linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
	Tim Harvey <tharvey@gateworks.com>,
	"kernel@pengutronix.de" <kernel@pengutronix.de>,
	"patchwork-lst@pengutronix.de" <patchwork-lst@pengutronix.de>
Subject: Re: [PATCH] PCI: dwc: skip MSI init if MSIs have been explicitly disabled
Date: Wed, 06 Mar 2019 12:39:07 +0100
Message-ID: <1551872347.9298.26.camel@pengutronix.de> (raw)
In-Reply-To: <9abfe0b2-edfc-a989-04d3-0dd143b7557b@synopsys.com>

Am Mittwoch, den 06.03.2019, 09:53 +0000 schrieb Gustavo Pimentel:
> Hi,
> 
> On 04/03/2019 20:18, Marc Zyngier wrote:
> > Hi both,
> > 
> > On Mon, 04 Mar 2019 19:39:45 +0000,
> > > > Lucas Stach <l.stach@pengutronix.de> wrote:
> > > 
> 
> (snipped)
> 
> > > > > 
> > > > > As MSI and legacy IRQs are already mutually exclusive on the DWC core,
> > > > > as the core won't forward any legacy IRQs once any MSI has been enabled,
> > > > > users wishing to use legacy IRQs already need to explictly disable MSI
> > > > > support (usually via the pci=nomsi kernel commandline option). To avoid
> > > > > any issues with MSI conflicting with legacy IRQs, just skip all of the
> > > > > DWC MSI initalization, including the IRQ line claim, when MSI is disabled.
> > > > 
> > > > Does this mean that if we have a device that uses legacy IRQs, the
> > > > user has to figure out to boot with "pci=nomsi"?
> > > 
> > > As long as there is only a single device connected and there are no
> > > port services things will work. If port services are active, those will
> > > start to use MSIs, breaking legacy IRQs in the process.
> > > 
> > > I've asked Synopsys if there is a workaround for this, but it seems
> > > that the core is working "as designed" with no workaround for this icky
> > > behavior.
> > 
> > Is this the general DWC controller behaviour? Or something that is
> > specific to a given implementation? I can't believe someone actually
> > thought this is an acceptable behaviour...
> > 
> > Gustavo, can you please check with your HW colleagues and let
> > everybody know what's the official Synopsys position on this?
> > 
> 
> Sure, I can ask the HW team to provide me more info about this, This can take a
> while. Unfortunately on my setup I only have MSI and MSI-X, therefore I can't
> really test what has been statemented.

At least this behavior was confirmed by Joao Pinto at Synopsys last
time the issue was discussed.

http://lists.infradead.org/pipermail/linux-arm-kernel/2017-April/499591.html

Regards,
Lucas

  reply index

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-02-27 16:52 Lucas Stach
2019-02-27 17:25 ` Fabio Estevam
2019-02-27 17:43   ` Tim Harvey
2019-02-28 13:29 ` Lorenzo Pieralisi
2019-03-01 10:10   ` Gustavo Pimentel
2019-03-01 12:29 ` Lorenzo Pieralisi
2019-03-04 19:25 ` Bjorn Helgaas
2019-03-04 19:39   ` Lucas Stach
2019-03-04 20:18     ` Marc Zyngier
2019-03-06  9:53       ` Gustavo Pimentel
2019-03-06 11:39         ` Lucas Stach [this message]
2019-03-06 15:59       ` Tim Harvey
2019-04-15 14:34       ` Gustavo Pimentel

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