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

From: "Anand, Jerome" <jerome.anand@intel.com>
To: "Thomas Gleixner" <tglx@linutronix.de>,
	"Ville Syrjälä" <ville.syrjala@linux.intel.com>
Cc: "Chen, Augustine" <augustine.chen@intel.com>,
	"intel-gfx@lists.freedesktop.org"
	<intel-gfx@lists.freedesktop.org>,
	"alsa-devel@alsa-project.org" <alsa-devel@alsa-project.org>,
	"Bossart, Pierre-louis" <pierre-louis.bossart@intel.com>,
	"tiwai@suse.de" <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" <linux-kernel@vger.kernel.org>
Subject: RE: [Intel-gfx] [PATCH] drm/i915: Remove unused IRQ chip data of HDMI LPE audio
Date: Mon, 11 Dec 2017 08:33:33 +0000	[thread overview]
Message-ID: <F6867404AABACB4D8EC371BF802A4B7C5790D206@fmsmsx101.amr.corp.intel.com> (raw)
In-Reply-To: <alpine.DEB.2.20.1712082340400.2301@nanos>

> -----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
> 

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.

> Curing the symptom is never a good approach.
> 
> Thanks,
> 
> 	tglx