On Sat, Jul 26, 2008 at 12:47 AM, Daniel Walker [off-list ref] wrote:

On Fri, 2008-07-25 at 22:45 -0400, Grant Likely wrote:

quoted

On Fri, Jul 25, 2008 at 2:19 PM, Daniel Walker [off-list ref] wrote:

quoted

On Fri, 2008-07-25 at 03:33 -0400, Grant Likely wrote:

quoted

+     if (status && (irq != NO_IRQ))
+             dev_err(&ms->master->dev, "spurious irq, status=0x%.2x\n",
+                     status);
+
+     /* Check if there is another transfer waiting */
+     if (list_empty(&ms->queue))
+             return FSM_STOP;

I don't think doing list_empty outside the critical section is totally
safe.. You might want to move it down inside the spin_lock() section.

This should be fine.  This is the only place where items are dequeued,
and it will only ever be called from the ISR or the work queue.  The
work queue and IRQ will never be active at the same time (I'll add a
comment to the fact).  It also looks like list_empty is perfectly safe
to call without the protection of a spin lock (but somebody correct me
if I'm out to lunch).  It doesn't dereference any of the pointers in
the list_head structure.

The list_empty wouldn't crash, but the result isn't necessarily
accurate.

It doesn't need to be accurate because the spinlock is obtained before
actually trying to dequeue anything.  Even if it held the spinlock
there would still be uncertainty depending on which routine ran first.
 If this function ran first, then it's going to stop the state machine
regardless and the enqueue function will have to kick it off again
anyway.

But, I've taken a look at the code, and you're right, the spin lock
does need to be held while running the state machine because I do have
a case where the IRQ and workqueue could get executed at the same
time.  I'll fix it up.

quoted

quoted

quoted

+     /* Get the next message */
+     spin_lock(&ms->lock);

The part that's a little confusing here is that the interrupt can
actually activate the workqueue .. So I'm wondering if maybe you could
have this interrupt driven any workqueue driven at the same time? If you
could then you would need the above to be
spin_lock_irq/spin_lock_irqsave ..

Ditto here, since the irq and workqueue are not enabled at the same
time there is no worry about collision.

Why are you waking up the work queue from inside the irq handler? You
might also want to break out the handling from inside the irq handler
and call that from the workqueue, instead of re-calling the irq handler
function from the workqueue.. It's a little confusing from a context
perspective.

Sure, I can rework that.  The irq handler would then just simply be a
straight call into the state machine runner.  I just dropped the
additional 4 lines of code for conciseness, but I can change it around
for clarity... actually, with the spin lock stuff above I need to do
this rework.

g.

-- 
Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.