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

To: David Daney <ddaney.cavm@gmail.com>
Subject: Re: [PATCH v6 4/5] MIPS: Octeon: Setup irq_domains for interrupts.
From: Rob Herring <robherring2@gmail.com>
Date: Fri, 09 Mar 2012 15:07:22 -0600
Cc: Grant Likely <grant.likely@secretlab.ca>, David Daney <david.s.daney@gmail.com>, "linux-mips@linux-mips.org" <linux-mips@linux-mips.org>, "ralf@linux-mips.org" <ralf@linux-mips.org>, "devicetree-discuss@lists.ozlabs.org" <devicetree-discuss@lists.ozlabs.org>, Rob Herring <rob.herring@calxeda.com>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
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On 03/09/2012 12:45 PM, David Daney wrote:
> On 03/08/2012 09:57 PM, Grant Likely wrote:
>> On Sat, 03 Mar 2012 21:09:32 -0800, David
>> Daney<david.s.daney@gmail.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.
>>
> 
> 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:

I'll just repeat what others have said: if it's not upstream it doesn't
exist.

We have no knowledge about out of tree h/w to understand what you need

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

How many actual hwirqs in each case and what is the range?

So for CIU3, it seems you would need to use a radix tree. CIU2 is
probably borderline depending on what is the max number. But because you
don't yet have code in tree for either yet, you can use a linear domain
for now. It shouldn't be hard to switch from linear to radix later.

> 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*.

OCTEON_IRQ_* values need to go. You may not have to do that now, but
certainly before doing support for CIU2 and CIU3 you do. Those platforms
should be DT only.

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

Yes. You're not the only one with this issue.

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

For a legacy boot yes. But when you boot with DT, you should not need
them. This is certainly possible as several ARM platforms do this. You
need to start with minimal set of drivers enabled for DT and add them
back in 1 by 1.

Rob

> 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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