Re: [Intel-gfx] [PATCH] drm/i915: Remove unused IRQ chip data of HDMI LPE audio

[Takashi Iwai]

On Mon, 11 Dec 2017 14:20:23 +0100,
Ville SyrjÃlà wrote:
> 
> On Mon, Dec 11, 2017 at 08:33:33AM +0000, Anand, Jerome wrote:
> > 
> > 
> > > -----Original Message-----
> > > From: Thomas Gleixner [mailto:tglx@xxxxxxxxxxxxx]
> > > Sent: Saturday, December 9, 2017 4:22 AM
> > > To: Ville SyrjÃlà <ville.syrjala@xxxxxxxxxxxxxxx>
> > > Cc: Chen, Augustine <augustine.chen@xxxxxxxxx>; intel-
> > > gfx@xxxxxxxxxxxxxxxxxxxxx; alsa-devel@xxxxxxxxxxxxxxxx; Anand, Jerome
> > > <jerome.anand@xxxxxxxxx>; Bossart, Pierre-louis <pierre-
> > > louis.bossart@xxxxxxxxx>; tiwai@xxxxxxx; Ingo Molnar <mingo@xxxxxxxxxx>;
> > > H. Peter Anvin <hpa@xxxxxxxxx>; Jiang Liu <jiang.liu@xxxxxxxxxxxxxxx>; Juergen
> > > Gross <jgross@xxxxxxxx>; Dou Liyang <douly.fnst@xxxxxxxxxxxxxx>; linux-
> > > kernel@xxxxxxxxxxxxxxx
> > > Subject: Re: [Intel-gfx] [PATCH] drm/i915: Remove unused IRQ chip data of
> > > HDMI LPE audio
> > > 
> > > On Fri, 8 Dec 2017, Ville SyrjÃlà 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.

IMO, the primary question is whether the usage of irq chip without irq
domain is valid or not.  If an irq domain is mandatory, that's the
thing to be fixed in i915 side.


thanks,

Takashi