Handling multiple GPIO controllers in 8xxx GPIO driver

Handling multiple GPIO controllers in 8xxx GPIO driver

[Felix Radensky]

Hi,

Looks like  8xxx GPIO driver cannot properly handle interrupts
when multiple GPIO controllers exist in the system.

On Freescale P1022 there are 3 GPIO controllers. All 3 use
the same interrupt line, internal interrupt 31. If all controllers
are defined in device tree set_irq_chained_handler() is invoked
3 times with same  hardware irq number. The result is interrupt
storm,  mpc8xxx_gpio_irq_cascade() is invoked indefinitely.

What would be the best way to fix the problem ?

Thanks.

Felix Radensky.

Re: Handling multiple GPIO controllers in 8xxx GPIO driver

[Grant Likely]

On Tue, Sep 27, 2011 at 04:59:28PM +0300, Felix Radensky wrote:
> Hi,
> 
> Looks like  8xxx GPIO driver cannot properly handle interrupts
> when multiple GPIO controllers exist in the system.
> 
> On Freescale P1022 there are 3 GPIO controllers. All 3 use
> the same interrupt line, internal interrupt 31. If all controllers
> are defined in device tree set_irq_chained_handler() is invoked
> 3 times with same  hardware irq number. The result is interrupt
> storm,  mpc8xxx_gpio_irq_cascade() is invoked indefinitely.
> 
> What would be the best way to fix the problem ?

The solution is to make the gpio driver register as a regular
interrupt handler, and not as a chained handler.

g.

Re: Handling multiple GPIO controllers in 8xxx GPIO driver

[Felix Radensky]

Hi Grant,

On 09/27/2011 09:29 PM, Grant Likely wrote:
> On Tue, Sep 27, 2011 at 04:59:28PM +0300, Felix Radensky wrote:
>> Hi,
>>
>> Looks like  8xxx GPIO driver cannot properly handle interrupts
>> when multiple GPIO controllers exist in the system.
>>
>> On Freescale P1022 there are 3 GPIO controllers. All 3 use
>> the same interrupt line, internal interrupt 31. If all controllers
>> are defined in device tree set_irq_chained_handler() is invoked
>> 3 times with same  hardware irq number. The result is interrupt
>> storm,  mpc8xxx_gpio_irq_cascade() is invoked indefinitely.
>>
>> What would be the best way to fix the problem ?
> The solution is to make the gpio driver register as a regular
> interrupt handler, and not as a chained handler.
>
> g.
>

You mean interrupt handler per GPIO pin ?

Felix.

Re: Handling multiple GPIO controllers in 8xxx GPIO driver

[Tabi Timur-B04825]

On Tue, Sep 27, 2011 at 1:29 PM, Grant Likely <grant.likely@secretlab.ca> w=
rote:

> The solution is to make the gpio driver register as a regular
> interrupt handler, and not as a chained handler.

I was wondering about that.

What exactly is a chained handler?  How is it different from a regular hand=
ler?

--=20
Timur Tabi
Linux kernel developer at Freescale=

Re: Handling multiple GPIO controllers in 8xxx GPIO driver

[Grant Likely]

On Wed, Sep 28, 2011 at 08:52:30PM +0000, Tabi Timur-B04825 wrote:
> On Tue, Sep 27, 2011 at 1:29 PM, Grant Likely <grant.likely@secretlab.ca> wrote:
> 
> > The solution is to make the gpio driver register as a regular
> > interrupt handler, and not as a chained handler.
> 
> I was wondering about that.
> 
> What exactly is a chained handler?  How is it different from a regular handler?

A chained handler has an expedited path through the interrupt code for
handling it (basically, it skips handling it at the parent controller
and passes through to the child, but it cannot handle multiple chained
children on a single irq input.

g.

Re: Handling multiple GPIO controllers in 8xxx GPIO driver

[Tabi Timur-B04825]

Grant Likely wrote:
> A chained handler has an expedited path through the interrupt code for
> handling it (basically, it skips handling it at the parent controller
> and passes through to the child, but it cannot handle multiple chained
> children on a single irq input.

So you can't do a shared chained handler?  If the chained handler returns=20
IRQ_NONE, the interrupt code just gives up?

Why is it called a "chained" handler?  Where's the chain?

I'm trying to understand the core interrupt code, and I can't seem to find=
=20
any descriptions of it.

--=20
Timur Tabi
Linux kernel developer at Freescale=

Re: Handling multiple GPIO controllers in 8xxx GPIO driver

[Felix Radensky]

Hi Grant,

On 09/29/2011 08:27 PM, Grant Likely wrote:
> On Wed, Sep 28, 2011 at 08:52:30PM +0000, Tabi Timur-B04825 wrote:
>> On Tue, Sep 27, 2011 at 1:29 PM, Grant Likely<grant.likely@secretlab.ca>  wrote:
>>
>>> The solution is to make the gpio driver register as a regular
>>> interrupt handler, and not as a chained handler.
>> I was wondering about that.
>>
>> What exactly is a chained handler?  How is it different from a regular handler?
> A chained handler has an expedited path through the interrupt code for
> handling it (basically, it skips handling it at the parent controller
> and passes through to the child, but it cannot handle multiple chained
> children on a single irq input.
>
> g.
>
I may be missing something, but please see this discussion:
http://comments.gmane.org/gmane.linux.ports.arm.kernel/76025

Chained handler is suggested as the solution for very similar problem.
(several peripherals sharing the same hardware IRQ line. If it's possible
on ARM, it should be doable on powerpc, right ?

Felix.

Re: Handling multiple GPIO controllers in 8xxx GPIO driver

[Grant Likely]

On Thu, Sep 29, 2011 at 08:22:06PM +0000, Tabi Timur-B04825 wrote:
> Grant Likely wrote:
> > A chained handler has an expedited path through the interrupt code for
> > handling it (basically, it skips handling it at the parent controller
> > and passes through to the child, but it cannot handle multiple chained
> > children on a single irq input.
> 
> So you can't do a shared chained handler?  If the chained handler returns 
> IRQ_NONE, the interrupt code just gives up?

No, you can do one or more regular handlers which acks or masks the
irq in the upstream controller, or you can do a single chained handler
which bypasses any ack/mask.  It's an optimization.  The code *could*
be modified to allow multiple chained handlers, but I cannot comment
on if it would be worthwhile.

Basically, a chained handler replaces the regular edge or level irq
handler.  Take a look at __irq_set_handler().  Chained in this case is
really a synonym for a cascaded irq handler.  Also, I believe it only
really works if the irq is level sensitive because an edge sensitive
irq would still need to be acked.  It would also need to be an irq
controller that can be accessed immediately since it depends on the
child controller to ack/mask it's inputs.  Something on an i2c bus
wouldn't work so well because the irq would remain asserted until
after several slow i2c transactions.

g.