Configurable interrupt sources, and DT bindings

[Rob Herring]

On 11/29/2011 08:24 PM, Stephen Warren wrote:
> Rob Herring wrote at Monday, November 28, 2011 4:24 PM:
>> On 11/28/2011 04:29 PM, Stephen Warren wrote:
>>> Many interrupt sinks support various of active high/low, rising/falling
>>> edge. This can already be configured by setting #interrupt-cells
>>> appropriately, and defining an interrupt-controller-specific binding for
>>> the additional cells.
>>>
>>> At least some interrupt sources have similar configurability in HW. An
>>> example is the WM8903 audio codec, which can generate both active high
>>> and active low interrupt signals.
>>>
>>> One possibility is to describe this directly in the binding for each
>>> interrupt source....
> ...
>>> However, given that interrupt sinks already know which signaling methods
>>> they support, and may be configured to accept a specific method per
>>> interrupt input using extra interrupt cells, perhaps the solution isn't
>>> to create a binding that the interrupt sink parses in isolation, but
>>> rather to create a new API within the kernel where the interrupt source
>>> can query the interrupt sink for a list of supported signaling methods,
>>> and pick one that it also supports, and use it. This list could be
>>> restricted based on the interrupts property's extra cells.
>>>
>>> What are people's thoughts here; should we go down this
>>> auto-configuration route, or just explicitly configure interrupt sources
>>> using a binding other than the interrupts property?
>>>
>>> Related, having this negotiation followed by a request_irq() passing the
>>> flags back to the sink seems a little redundant, but I suppose if the
>>> sink is configurable and unconstrained, this is necessary.
>>
>> I think adding another property is the wrong approach. The information
>> is already there in the interrupt binding. irq_create_of_mapping almost
>> does what you need. Perhaps it could be extended to return the type as
>> part of the irq resource. There are already defined resource bits for this:
>>
>> /* PnP IRQ specific bits (IORESOURCE_BITS) */
>> #define IORESOURCE_IRQ_HIGHEDGE		(1<<0)
>> #define IORESOURCE_IRQ_LOWEDGE		(1<<1)
>> #define IORESOURCE_IRQ_HIGHLEVEL	(1<<2)
>> #define IORESOURCE_IRQ_LOWLEVEL		(1<<3)
>>
>> It may be a bit problematic to change irq_create_of_mapping as Sparc has
>> a different version.
> 
> Taking a look at the code, I think it can work like this:
> 
> * Except for SPARC, irq_of_parse_and_map() calls irq_create_of_mapping(),
>   which calls the IRQ chip's dt_translate() function which can return the
>   type from the interrupt specifier in DT, and if it did, the type is
>   passed to irq_set_irq_type().
> 
> * SPARC's custom irq_of_parse_and_map() doesn't call irq_set_irq_type()
>   as far as I can tell. I think we can just ignore this for now; if SPARC
>   wants to participate in this scheme, its custom irq_of_parse_and_map()
>   could be enhanced appropriately.
> 
> * I assert that all IRQ chips that want to participate must define an
>   interrupt specifier DT binding that defines the trigger type; e.g.
>   that implemented by using irq_domain_add_simple() and #interrupt-cells
>   greater than 1.
> 
> * I assert that all IRQ chips that want to participate must call
>   irqd_set_trigger_type() from their irq_set_type op. This will cache the
>   type for later access. This call is missing from Tegra's GPIO interrupt
>   controller, but can easily be added.
> 
> * Create a new function that drivers can call on their Linux interrupt ID,
>   which internally calls irqd_get_trigger_type(). This will return the
>   configured type, and they can adjust their interrupt output pin
>   appropriately, or fail to probe if they can't support the selected type.
> 
> * We can probably remove any platform data fields that configure a device's
>   interrupt output type (e.g. WM8903 has an irq_active_low field in pdata)
>   and replace it with this scheme. If that won't work, we can have drivers
>   call the new API only when instantiated from DT, so they continue to
>   work unchanged in the non-DT case.
> 
> Does that sound like a reasonable solution? If so, I can start hooking this
> together.

Sounds good to me.

Rob