[PATCH] pcmcia: fix sharing IRQs and request_irq without IRQ_HANDLE_PRESENT

Debugging and description from: Noah Misch <[e-mail]>

When a driver calls pcmcia_request_irq with IRQ_HANDLE_PRESENT unset, it looks
for an open IRQ by request_irq()ing with a dummy handler and NULL dev_info.
free_irq uses dev_info as a key for identifying the handler to free among
those sharing an IRQ, so request_irq returns -EINVAL if dev_info is NULL and
the IRQ may be shared. That unknown error code is the -EINVAL.

It looks like only pcnet_cs and axnet_cs are affected. Most other drivers let
pcmcia_request_irq install their interrupt handlers. sym53c500_cs requests
its IRQ manually, but it cannot share an IRQ.

The appended patch changes pcmcia_request_irq to pass an arbitrary, unique,
non-NULL dev_info with the dummy handler.

Signed-off-by: Dominik Brodowski <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/pcmcia/pcmcia_resource.c

···
 	} else {
 		int try;
 		u32 mask = s->irq_mask;
-		void *data = NULL;
+		void *data = &p_dev->dev.driver; /* something unique to this device */
 
 		for (try = 0; try < 64; try++) {
 			irq = try % 32;