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

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Date:   Tue, 12 Dec 2017 18:06:41 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Anand, Jerome" <jerome.anand@...el.com>
cc:     Ville Syrjälä <ville.syrjala@...ux.intel.com>,
        "Chen, Augustine" <augustine.chen@...el.com>,
        "intel-gfx@...ts.freedesktop.org" <intel-gfx@...ts.freedesktop.org>,
        "alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
        "Bossart, Pierre-louis" <pierre-louis.bossart@...el.com>,
        "tiwai@...e.de" <tiwai@...e.de>, Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Jiang Liu <jiang.liu@...ux.intel.com>,
        Juergen Gross <jgross@...e.com>,
        Dou Liyang <douly.fnst@...fujitsu.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [Intel-gfx] [PATCH] drm/i915: Remove unused IRQ chip data of
 HDMI LPE audio

On Mon, 11 Dec 2017, Anand, Jerome wrote:
> > 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.

APIC code does not even see that interrupt at all. It's completely
disconnected.

> > > > 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.

That still does not explain why this is broken with
CONFIG_CPUMASK_OFFSTACK=n and cpu hotplug.

Thanks,

	tglx