linux-kernel - Re: [PATCH v6 4/5] MIPS: Octeon: Setup irq

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Message-Id: <20120309055704.465823E0901@localhost>
Date:	Thu, 08 Mar 2012 22:57:04 -0700
From:	Grant Likely <grant.likely@...retlab.ca>
To:	David Daney <david.s.daney@...il.com>,
	Rob Herring <robherring2@...il.com>
Cc:	David Daney <david.daney@...ium.com>,
	David Daney <ddaney.cavm@...il.com>,
	"linux-mips@...ux-mips.org" <linux-mips@...ux-mips.org>,
	"ralf@...ux-mips.org" <ralf@...ux-mips.org>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	Rob Herring <rob.herring@...xeda.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 4/5] MIPS: Octeon: Setup irq_domains for interrupts.

On Sat, 03 Mar 2012 21:09:32 -0800, David Daney <david.s.daney@...il.com> wrote:
> On 03/03/2012 11:35 AM, Rob Herring wrote:
> > On 03/02/2012 01:29 PM, David Daney wrote:
> >> On 03/02/2012 11:07 AM, Grant Likely wrote:
> >>> +static void __init octeon_irq_set_ciu_mapping(unsigned int irq,
> >>> +                          unsigned int line,
> >>> +                          unsigned int bit,
> >>> +                          struct irq_domain *domain,
> >>>                               struct irq_chip *chip,
> >>>                               irq_flow_handler_t handler)
> >>>     {
> >>> +    struct irq_data *irqd;
> >>>         union octeon_ciu_chip_data cd;
> >>>
> >>>         irq_set_chip_and_handler(irq, chip, handler);
> >>> -
> >>>         cd.l = 0;
> >>>         cd.s.line = line;
> >>>         cd.s.bit = bit;
> >>>
> >>>         irq_set_chip_data(irq, cd.p);
> >>>         octeon_irq_ciu_to_irq[line][bit] = irq;
> >>> +
> >>> +    irqd = irq_get_irq_data(irq);
> >>> +    irqd->hwirq = line<<    6 | bit;
> >>> +    irqd->domain = domain;
> >>>>> I think the domain code will set these.
> >>>> It is my understanding that the domain code only does this for:
> >>>>
> >>>> o irq_domain_add_legacy()
> >>>>
> >>>> o irq_create_direct_mapping()
> >>>>
> >>>> o irq_create_mapping()
> >>>>
> >>>> We use none of those.  So I do it here.
> >>>>
> >>>> If there is a better way, I am open to suggestions.
> >>> irq_create_mapping is called by irq_create_of_mapping() which is
> >>> in turn called by irq_of_parse_and-map().  irq_domain always
> >>> manages the hwirq and domain values.  Driver code cannot manipulate
> >>> them manually.
> >>>
> >> I really must be missing something.
> >>
> >> Given:
> >>
> >> 1) I must have a mapping between hwirq and irq that I control so that
> >> non-OF code using the OCTEON_IRQ_* constants continues to work.
> > Those defines are what you need to work to get rid of.
> 
> We are not starting from a blank slate here.  There is a lot of in-tree 
> code using these symbols.  We cannot make them disappear with wishful 
> thinking.
> 
> The first step is a switch to irq_domains using the existing mappings.
> 
> After we do that, I have patches to transition some drivers to use the 
> OF mapping via irq_domains.  After those are merged, we can work toward 
> getting rid of OCTEON_IRQ_*.  But I think it must be the last step in 
> the process, not the first.
> >
> >> 2) irq_create_mapping() will allocate a random irq value if none is
> >> already assigned to the hwirq.
> >>
> >> Therefore: To avoid having random irq values assigned, I must manually
> >> assign them.
> >>
> > So you should be using legacy domain if you need to maintain fixed hwirq
> > to linux irq numbers. "linear" is a bit confusing as it doesn't mean
> > linear 1:1 irq number assignment, but linear search.
> 
> My reading of Grant's code in linux-next directly contradicts this 
> statement.  There is no code in irqdomain.c, that I can see, that allows 
> me to have an arbitrary mapping of irq <--> hwirq values.

There are 4 kinds of mappings available; legacy, linear, radix and nomap.

Ignore nomap and radix; you don't want them.

legacy maps a contiguous range of hwirq numbers to a contiguous range of
linux irq numbers.  To preserve the exising #define mappings but still add
DT support, this is the one that you want.  The downside is that it requires
all the irq_descs to be allocated ahead of time (which probably isn't a
problem for you).

The linear map has a linear reverse map lookup table that allows arbitrary
irq <--> hwirq mappings.  This mapping is preferred, but it doesn't work
if you need to preserve #defined irq mappings.

g.
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