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

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Message-ID: <20171211132023.GO10981@intel.com>
Date:   Mon, 11 Dec 2017 15:20:23 +0200
From:   Ville Syrjälä <ville.syrjala@...ux.intel.com>
To:     "Anand, Jerome" <jerome.anand@...el.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        "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, Dec 11, 2017 at 08:33:33AM +0000, Anand, Jerome wrote:
> 
> 
> > -----Original Message-----
> > From: Thomas Gleixner [mailto:tglx@...utronix.de]
> > Sent: Saturday, December 9, 2017 4:22 AM
> > To: Ville Syrjälä <ville.syrjala@...ux.intel.com>
> > Cc: Chen, Augustine <augustine.chen@...el.com>; intel-
> > gfx@...ts.freedesktop.org; alsa-devel@...a-project.org; Anand, Jerome
> > <jerome.anand@...el.com>; Bossart, Pierre-louis <pierre-
> > louis.bossart@...el.com>; 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
> > 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