Re: [PATCH v6 4/5] MIPS: Octeon: Setup irq_domains for interrupts.

[David Daney]

On 03/08/2012 09:57 PM, Grant Likely wrote:
> On Sat, 03 Mar 2012 21:09:32 -0800, David Daney<david.s.daney@xxxxxxxxx>  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.

Yes, I had discovered that.

> 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.

This is precisely the point that you and Rob seem to have missed in the 
last three or four back-and-forths about this.

Probably I have not explained well enough why legacy will not work.

We have three different interrupt controllers (although only one is 
currently in-tree).  hwirq to irq mapping for them is more or less as 
follows:

irq                 hwirqCIU        hwirqCIU2      hwirqCIU3
----------------------------------------------------------------------
OCTEON_IRQ_USB0     56               81             934562
OCTEON_IRQ_TWSI     45              224             100543
OCTEON_IRQ_UART0    34              228               4572
.
.
.

Now what we notice here is that there is no possible 1:1 linearly 
increasing mapping possible for the irq and *all* three hwirq sets.  We 
want a single binary that contains support for all three interrupt 
controllers, so the OCTEON_IRQ_* values have to be the same for all 
three interrupt controllers.  Because of this, legacy mapping is 
*impossible*.

Since the possible ranges of the hwirq values is very large and quite 
sparse, probably the radix mapping will be required.

Also to support non-OF drivers and architecture specific code for the 
near future, I really think the existing IRQ values *must* be preserved.

Therefore, as I said above, we need a way for my SOC/board code to 
specify the mapping.

Perhaps we need to add an optional function to struct irq_domain_ops 
that would allow the default mapping to be overridden on a per 
irq_domain basis.

Otherwise, I think I will have to keep poking into the internal 
irq_domain data structures to get the mappings I want.

What do you think?

David Daney
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