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

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Date:	Sat, 03 Mar 2012 21:09:32 -0800
From:	David Daney <david.s.daney@...il.com>
To:	Rob Herring <robherring2@...il.com>
CC:	David Daney <david.daney@...ium.com>,
	Grant Likely <grant.likely@...retlab.ca>,
	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 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.


>
> Ultimately, for DT boot you should use of_irq_init to scan the dts, and
> then create a linear domain for each interrupt controller node. You may
> need to decide on linear vs. legacy at runtime based on having a DT node
> pointer or not.

Perhaps, but we need to take the first step before gradually arriving at 
some Ultimate Solution.

We will also need to handle irq controllers with 2^20 sparsely populated 
hwirq values, so linear domains will probably be out of the question there.

David Daney
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