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SubjectRe: [Intel-gfx] [PATCH] drm/i915: Remove unused IRQ chip data of HDMI LPE audio
On Mon, Dec 11, 2017 at 08:33:33AM +0000, Anand, Jerome wrote:
>
>
> > -----Original Message-----
> > From: Thomas Gleixner [mailto:tglx@linutronix.de]
> > Sent: Saturday, December 9, 2017 4:22 AM
> > To: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > Cc: Chen, Augustine <augustine.chen@intel.com>; intel-
> > gfx@lists.freedesktop.org; alsa-devel@alsa-project.org; Anand, Jerome
> > <jerome.anand@intel.com>; Bossart, Pierre-louis <pierre-
> > louis.bossart@intel.com>; tiwai@suse.de; Ingo Molnar <mingo@redhat.com>;
> > H. Peter Anvin <hpa@zytor.com>; Jiang Liu <jiang.liu@linux.intel.com>; Juergen
> > Gross <jgross@suse.com>; Dou Liyang <douly.fnst@cn.fujitsu.com>; linux-
> > kernel@vger.kernel.org
> > Subject: Re: [Intel-gfx] [PATCH] drm/i915: Remove unused IRQ chip data of
> > HDMI LPE audio
> >
> > On Fri, 8 Dec 2017, Ville Syrjälä wrote:
> >
> > > On Fri, Dec 08, 2017 at 05:33:23PM +0800, Augustine.Chen wrote:
> > > > The chip data of HDMI LPE audio is set to drm_i915_private which is
> > > > not consistent with the expectation by x86 APIC driver.
> > >
> > > Hmm. Why is the apic code looking at data for an irq chip it hasn't
> > > created?
> > >
>
> apic code expects an irq domain to be place as generic approach.
>
> > > Do we need something like
> > > - dev_priv->lpe_audio.irq = irq_alloc_desc(0);
> > > + dev_priv->lpe_audio.irq = irq_alloc_desc(-1);
> >
> > #define irq_alloc_desc(node)
> >
> > So instead of handing in node 0 you hand in node -1 which is NUMA_NO_NODE
> >

Ah. I misread the macros. So we already pass irq=-1.

>
> Agree - am not sure whether it will make any difference.
>
> > > That *looks* more correct to me based on a cursory glance at the x86
> > > code, but I didn't trawl very deeply.
> >
> > The x86 core cares not at all about interrupt chips which are created in a driver
> > and not connected to an actual apic/ioapic/msi interrupt. This interrupt chip is
> > its own thing as we have others in GPIO etc.
> >
> > > > In the case of not enabling CONFIG_CPUMASK_OFFSTACK, this would
> > > > cause kernel panic while doing CPU hotplug.
> >
> > And why so? Surely not because you set irq_chip_data. That's really no
> > explanation at all.
> >
>
> Ideally, I feel there needs to be an irq domain for mapping the irq numbers with hwirq.
> It is not created as part of the hdmi lpe audio bridge.
> Since the logic to mask/unmask lpe audio interrupts is removed, there is no need of the
> Chip data or creation of the domain now.

There is no need right now. But there might be a need in the future.
LPE audio isn't even the only piece of hardware whose irq goes through
the i915 display engine (there's also the ISP and VED). So I would
much prefer a proper solution instead of sweeping the problem under
the rug.

--
Ville Syrjälä
Intel OTC

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