linux-kernel - Re: [PATCH v3 24/25] irq_domain: remove "hint" when allocating irq numbers

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Message-ID: <20120215215001.GA30946@r65073-Latitude-D630>
Date:	Wed, 15 Feb 2012 13:50:02 -0800
From:	Shawn Guo <shawn.guo@...aro.org>
To:	Grant Likely <grant.likely@...retlab.ca>
Cc:	Nicolas Ferre <nicolas.ferre@...el.com>,
	devicetree-discuss@...ts.ozlabs.org,
	Rob Herring <rob.herring@...xeda.com>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	linux-kernel@...r.kernel.org, Milton Miller <miltonm@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linuxppc-dev@...ts.ozlabs.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 24/25] irq_domain: remove "hint" when allocating irq
 numbers

On Wed, Feb 15, 2012 at 01:21:45PM -0700, Grant Likely wrote:
> On Wed, Feb 15, 2012 at 04:04:28PM +0100, Nicolas Ferre wrote:
> > On 02/07/2012 07:07 PM, Nicolas Ferre :
> > > On 01/27/2012 10:36 PM, Grant Likely :
> > >> The 'hint' used to try and line up irq numbers with hw irq numbers is
> > >> rather a hack and not very useful.  Now that /proc/interrupts also outputs
> > >> the hwirq number, it is even less useful to keep around the 'hint' heuristic.
> > >>
> > >> This patch removes it.
> > > 
> > > Grant,
> > > 
> > > While trying your patch series in conjunction with Rob one, I do not
> > > find this patch in your irqdomain/next branch (and a couple of others).
> > > Can you tell me if this v3 series is available as a git tree?
> > 
> > I am still interested by patch 24-25 of this series but still cannot
> > find them in your irqdomain/next branch:
> > Are they also expected to join the 3.4 merge window material?
> 
> I've held off on putting them in irqdomain/next because they are a bit more
> risky than the other patches, and I want an explicit ack from Ben for patches
> 24 & 25.  However, that shouldn't really cause any issues since the changes
> in 24 & 25 don't impact the irq_domain functionality or API.  They are just
> optimizations.
> 
I'm seeing that patch 24 does impact on irq_domain functionality
a little bit.  On next tree which has no this patch yet,
irq_create_mapping can reasonably create virq in range 1..15, while
irq_find_mapping will only try to find the virq from 16
(NUM_ISA_INTERRUPTS).  This will result in that any hwirq that is < 16
gets multiple entries in the mapping table with different virq numbers
mapped to the same one hwirq.

That's why I have to apply patch #24 (with one line change below) on
top of next tree to get my imx irqdomain series work properly.

@@ -371,7 +371,7 @@ unsigned int irq_create_mapping(struct irq_domain *domain,
                return irq_domain_legacy_revmap(domain, hwirq);
 
        /* Allocate a virtual interrupt number */
-       virq = irq_alloc_desc(0);
+       virq = irq_alloc_desc_from(1, 0);
        if (!virq) {
                pr_debug("irq: -> virq allocation failed\n");
                return 0;

I need this line of change, because the first call on irq_alloc_desc
will always return 0 to virq and in turn irq_create_mapping fails.
On imx, that's the mapping for timer irq.  Hence, the system will hang
there due to irq mapping failure.

-- 
Regards,
Shawn
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