Re: [PATCH][RESEND] i2c-i801: Add basic interrupt support

[Jean Delvare <khali-PUYAD+kWke1g9hUCZPvPmw@public.gmane.org>]

On Sat, 16 Aug 2008 18:50:13 +0200, Jean Delvare wrote:
> On Sat, 16 Aug 2008 18:22:36 +0200, Ivo Manca wrote:
> > Great and thanks. Am really curious about the stability of this code :)
> 
> I'm hitting the first problems, with SMBus block transactions. They
> fail on my ICH3 with use_irq=1. That's strange because these
> transactions shouldn't make use of interrupts on the ICH3, but I still
> see the IRQ handler being called 3 times, and then the transaction
> times out. I'm debugging this now.

OK, I see what's going on. On this laptop, IRQ 9 is used by many
things, not just SMBus. So the interrupt handler keeps being called even
without SMBus activity or with polled-based SMBus activity. That's what
happens during SMBus block transactions: the interrupt handler is
called but not for us. However the interrupt handler thinks it is
called by us and clears the status register value. This causes the
polled-based loop to wait forever: by the time it looks for the status
register value, it has been cleared.

So we need to change the code in either of three ways:
* Drop support for byte-by-byte block transactions.
* Inhibit the interrupt handler during polled-based block transactions.
* Convert the byteb-by-byte block transaction code to use interrupts
  instead of polling.
The latter would be cleaner, but that's also more work.

-- 
Jean Delvare

_______________________________________________
i2c mailing list
i2c-GZX6beZjE8VD60Wz+7aTrA@public.gmane.org
http://lists.lm-sensors.org/mailman/listinfo/i2c