resource: shared I/O region support

SuperIO devices share regions and use lock/unlock operations to chip
select.  We therefore need to be able to request a resource and wait for
it to be freed by whichever other SuperIO device currently hogs it.
Right now you have to poll which is horrible.

Add a MUXED field to IO port resources. If the MUXED field is set on the
resource and on the request (via request_muxed_region) then we block
until the previous owner of the muxed resource releases their region.

This allows us to implement proper resource sharing and locking for
superio chips using code of the form

enable_my_superio_dev() {
	request_muxed_region(0x44, 0x02, "superio:watchdog");
	outb() ..sequence to enable chip
}

disable_my_superio_dev() {
	outb() .. sequence of disable chip
	release_region(0x44, 0x02);
}

Signed-off-by: Giel van Schijndel <me@mortis.eu>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>

1 files changed, 15 insertions, 1 deletions

diff --git a/kernel/resource.c b/kernel/resource.c
index 9c358e2..7b36976 100644
--- a/kernel/resource.c
+++ b/kernel/resource.c
@@ -15,6 +15,7 @@
 #include <linux/spinlock.h>
 #include <linux/fs.h>
 #include <linux/proc_fs.h>
+#include <linux/sched.h>
 #include <linux/seq_file.h>
 #include <linux/device.h>
 #include <linux/pfn.h>
@@ -681,6 +682,8 @@ resource_size_t resource_alignment(struct resource *res)
  * release_region releases a matching busy region.
  */
 
+static DECLARE_WAIT_QUEUE_HEAD(muxed_resource_wait);
+
 /**
  * __request_region - create a new busy resource region
  * @parent: parent resource descriptor
@@ -693,6 +696,7 @@ struct resource * __request_region(struct resource *parent,
 				   resource_size_t start, resource_size_t n,
 				   const char *name, int flags)
 {
+	DECLARE_WAITQUEUE(wait, current);
 	struct resource *res = kzalloc(sizeof(*res), GFP_KERNEL);
 
 	if (!res)
@@ -717,7 +721,15 @@ struct resource * __request_region(struct resource *parent,
 			if (!(conflict->flags & IORESOURCE_BUSY))
 				continue;
 		}
-
+		if (conflict->flags & flags & IORESOURCE_MUXED) {
+			add_wait_queue(&muxed_resource_wait, &wait);
+			write_unlock(&resource_lock);
+			set_current_state(TASK_UNINTERRUPTIBLE);
+			schedule();
+			remove_wait_queue(&muxed_resource_wait, &wait);
+			write_lock(&resource_lock);
+			continue;
+		}
 		/* Uhhuh, that didn't work out.. */
 		kfree(res);
 		res = NULL;
@@ -791,6 +803,8 @@ void __release_region(struct resource *parent, resource_size_t start,
 				break;
 			*p = res->sibling;
 			write_unlock(&resource_lock);
+			if (res->flags & IORESOURCE_MUXED)
+				wake_up(&muxed_resource_wait);
 			kfree(res);
 			return;
 		}