Hi,
On Mon, Apr 07, 2008 at 07:13:48AM +1000, David McCullough wrote:
>
> Jivin Wolfgang Wegner lays it down ...
> > In my I2C driver, the code is the following:
> >
> > static
> > irqreturn_t coldfire_i2c_interrupt(int irq, void *dev_id)
> > {
> > /* check if we are called with the correct IRQ number */
> > if(irq != (MCFINT_VECBASE + MCFINT_I2C))
> > return IRQ_NONE;
> >
> > /* check if I2C int flag is set and send the event to waiting queue */
> > if(*MCF_I2C_I2SR & MCF_I2C_I2SR_IIF) {
> > *MCF_I2C_I2SR &= ~MCF_I2C_I2SR_IIF;
> > atomic_set(&coldfire_i2c_irq_happened, 1);
> > wake_up_interruptible(&coldfire_i2c_queue);
> > }
> > return IRQ_HANDLED;
> > }
> >
> > static int coldfire_wait_transfer(void) {
> >
> > int timeout;
> >
> > /* wait for data transfer to complete */
> > timeout = wait_event_interruptible_timeout(coldfire_i2c_queue,
> > 1 ==
> > atomic_read(&coldfire_i2c_irq_happened),
> > COLDFIRE_I2C_TIMEOUT);
> >
>
> What happens if you get an interrupt between here ...
>
> > if ((timeout <= 0 ) || (*MCF_I2C_I2SR & MCF_I2C_I2SR_IAL)) {
> > printk("wt: timeout = %d, I2SR = %x\n, ih = %d",timeout,
> > *MCF_I2C_I2SR, atomic_read(&coldfire_i2c_irq_happened));
> > return -1;
> > }
> > else {
>
> And here ? Won't coldfire_i2c_irq_happened get cleared when an
> interrupt service is pending ?
you are right, this is a problem that could happen in theory - but on
the other hand there should be one and exactly one interrupt while waiting
for the transfer to complete, so I can not see where the other execution
thread triggering the second interrupt should come from.
> Just check the HW in coldfire_wait_transfer,
>
> while (1) {
> spinlock_irq(xxx)
> irqpending = (*MCF_I2C_I2SR & MCF_I2C_I2SR_IAL);
> spinunlock_irq(xxx)
> if (irqpending) {
> /* remember to protect HW register accesses in here */
> service interrupt
> }
> }
Well, maybe I got it wrong, but to me this looks like a busy wait,
which is clearly not what I want a 200+ MHz processor to do while
waiting for a slow bus like I2C.
Regards,
Wolfgang
_______________________________________________
uClinux-dev mailing list
[email protected]
http://mailman.uclinux.org/mailman/listinfo/uclinux-dev
This message was resent by [email protected]
To unsubscribe see:
http://mailman.uclinux.org/mailman/options/uclinux-dev
