Re: lockdep and threaded IRQs (was: ...)

David Brownell
2009-03-01T22:11:57Z

On Saturday 28 February 2009, Thomas Gleixner wrote:
> > Got a version that applies to mainline GIT?
>
> http://tglx.de/~tglx/patches.tar.bz2

Very lightly tested patch appended ... it works
with the RTC IRQs, and there's no reason to think
any of the other not-chained-any-longer IRQs would
fail. This doesn't change anything the irqthread
does, just how it's created and accessed.

- Dave

=====
Minimalist patch to twl4030-irq.c to use the new threaded IRQ
stuff. For review, not merge; the original irq thread isn't
properly formatted any more -- to make the patch be as small as
possible.

This makes creating the IRQ thread a bit simpler, but the lack
of irq chaining support makes /proc/interrupts be wrong. The
quickcheck code path necessarily grew longer than the previous
irq_desc.handle() code path.

---
drivers/mfd/twl4030-irq.c | 88 +++++++++++---------------------------------
1 file changed, 23 insertions(+), 65 deletions(-)

--- a/drivers/mfd/twl4030-irq.c
+++ b/drivers/mfd/twl4030-irq.c
@@ -172,46 +172,23 @@ static const struct sih sih_modules[6] =

static unsigned twl4030_irq_base;

-static struct completion irq_event;
-
/*
- * This thread processes interrupts reported by the Primary Interrupt Handler.
+ * Threaded IRQ handler, processing interrupts reported by
+ * the Primary Interrupt Handler module.
*/
-static int twl4030_irq_thread(void *data)
+static irqreturn_t twl4030_pih_handler(int irq, void *unused)
{
- long irq = (long)data;
- struct irq_desc *desc = irq_to_desc(irq);
- static unsigned i2c_errors;
- const static unsigned max_i2c_errors = 100;
-
- if (!desc) {
- pr_err("twl4030: Invalid IRQ: %ld\n", irq);
- return -EINVAL;
- }
-
- current->flags |= PF_NOFREEZE;
-
- while (!kthread_should_stop()) {
int ret;
int module_irq;
u8 pih_isr;

- /* Wait for IRQ, then read PIH irq status (also blocking) */
- wait_for_completion_interruptible(&irq_event);
-
+ ret = IRQ_NONE;
ret = twl4030_i2c_read_u8(TWL4030_MODULE_PIH, &pih_isr,
REG_PIH_ISR_P1);
if (ret) {
pr_warning("twl4030: I2C error %d reading PIH ISR\n",
ret);
- if (++i2c_errors >= max_i2c_errors) {
- printk(KERN_ERR "Maximum I2C error count"
- " exceeded. Terminating %s.\n",
- __func__);
- break;
- }
- complete(&irq_event);
- continue;
+ goto done;
}

/* these handlers deal with the relevant SIH irq status */
@@ -225,7 +202,7 @@ static int twl4030_irq_thread(void *data
if (!d) {
pr_err("twl4030: Invalid SIH IRQ: %d\n",
module_irq);
- return -EINVAL;
+ continue;
}

/* These can't be masked ... always warn
@@ -234,44 +211,31 @@ static int twl4030_irq_thread(void *data
if (d->status & IRQ_DISABLED)
note_interrupt(module_irq, d,
IRQ_NONE);
- else
+ else {
d->handle_irq(module_irq, d);
+ ret = IRQ_HANDLED;
+ }
}
}
local_irq_enable();

- desc->chip->unmask(irq);
- }
-
- return 0;
+done:
+ /* unmask the IRQ; it retriggers as needed */
+ enable_irq(irq);
+ return ret;
}

/*
- * handle_twl4030_pih() is the desc->handle method for the twl4030 interrupt.
- * This is a chained interrupt, so there is no desc->action method for it.
* Now we need to query the interrupt controller in the twl4030 to determine
* which module is generating the interrupt request. However, we can't do i2c
* transactions in interrupt context, so we must defer that work to a kernel
- * thread. All we do here is acknowledge and mask the interrupt and wakeup
+ * thread. All we do here is mask the active-low interrupt and wakeup
* the kernel thread.
*/
-static void handle_twl4030_pih(unsigned int irq, irq_desc_t *desc)
-{
- /* Acknowledge, clear *AND* mask the interrupt... */
- desc->chip->ack(irq);
- complete(&irq_event);
-}
-
-static struct task_struct *start_twl4030_irq_thread(long irq)
+static irqreturn_t twl4030_pih_quickcheck(int irq, void *unused)
{
- struct task_struct *thread;
-
- init_completion(&irq_event);
- thread = kthread_run(twl4030_irq_thread, (void *)irq, "twl4030-irq");
- if (!thread)
- pr_err("twl4030: could not create irq %ld thread!\n", irq);
-
- return thread;
+ disable_irq(irq);
+ return IRQ_WAKE_THREAD;
}

/*----------------------------------------------------------------------*/
@@ -691,7 +655,6 @@ int twl_init_irq(int irq_num, unsigned i

int status;
int i;
- struct task_struct *task;

/*
* Mask and clear all TWL4030 interrupts since initially we do
@@ -733,18 +696,13 @@ int twl_init_irq(int irq_num, unsigned i
goto fail;
}

- /* install an irq handler to demultiplex the TWL4030 interrupt */
- task = start_twl4030_irq_thread(irq_num);
- if (!task) {
- pr_err("twl4030: irq thread FAIL\n");
- status = -ESRCH;
- goto fail;
- }
-
- set_irq_data(irq_num, task);
- set_irq_chained_handler(irq_num, handle_twl4030_pih);
+ /* FIXME should be a "chained" handler else irq statistics lie */
+ status = request_threaded_irq(irq_num,
+ twl4030_pih_handler, twl4030_pih_quickcheck,
+ IRQF_THREADED, "twl4030", NULL);

- return status;
+ if (status == 0)
+ return status;

fail:
for (i = irq_base; i < irq_end; i++)