DCA: Add Direct Cache Access driver

Direct Cache Access (DCA) is a method for warming the CPU cache before data
is used, with the intent of lessening the impact of cache misses.  This
patch adds a manager and interface for matching up client requests for DCA
services with devices that offer DCA services.

In order to use DCA, a module must do bus writes with the appropriate tag
bits set to trigger a cache read for a specific CPU.  However, different
CPUs and chipsets can require different sets of tag bits, and the methods
for determining the correct bits may be simple hardcoding or may be a
hardware specific magic incantation.  This interface is a way for DCA
clients to find the correct tag bits for the targeted CPU without needing
to know the specifics.

    [Dave Miller] use DEFINE_SPINLOCK()

Signed-off-by: Shannon Nelson <shannon.nelson@intel.com>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 88 insertions, 0 deletions

diff --git a/drivers/dca/dca-sysfs.c b/drivers/dca/dca-sysfs.c
new file mode 100644
index 000000000000..24a263b6844c
--- /dev/null
+++ b/drivers/dca/dca-sysfs.c
@@ -0,0 +1,88 @@
+#include <linux/kernel.h>
+#include <linux/spinlock.h>
+#include <linux/device.h>
+#include <linux/idr.h>
+#include <linux/kdev_t.h>
+#include <linux/err.h>
+#include <linux/dca.h>
+
+static struct class *dca_class;
+static struct idr dca_idr;
+static spinlock_t dca_idr_lock;
+
+int dca_sysfs_add_req(struct dca_provider *dca, struct device *dev, int slot)
+{
+	struct class_device *cd;
+
+	cd = class_device_create(dca_class, dca->cd, MKDEV(0, slot + 1),
+				 dev, "requester%d", slot);
+	if (IS_ERR(cd))
+		return PTR_ERR(cd);
+	return 0;
+}
+
+void dca_sysfs_remove_req(struct dca_provider *dca, int slot)
+{
+	class_device_destroy(dca_class, MKDEV(0, slot + 1));
+}
+
+int dca_sysfs_add_provider(struct dca_provider *dca, struct device *dev)
+{
+	struct class_device *cd;
+	int err = 0;
+
+idr_try_again:
+	if (!idr_pre_get(&dca_idr, GFP_KERNEL))
+		return -ENOMEM;
+	spin_lock(&dca_idr_lock);
+	err = idr_get_new(&dca_idr, dca, &dca->id);
+	spin_unlock(&dca_idr_lock);
+	switch (err) {
+	case 0:
+		break;
+	case -EAGAIN:
+		goto idr_try_again;
+	default:
+		return err;
+	}
+
+	cd = class_device_create(dca_class, NULL, MKDEV(0, 0),
+				 dev, "dca%d", dca->id);
+	if (IS_ERR(cd)) {
+		spin_lock(&dca_idr_lock);
+		idr_remove(&dca_idr, dca->id);
+		spin_unlock(&dca_idr_lock);
+		return PTR_ERR(cd);
+	}
+	dca->cd = cd;
+	return 0;
+}
+
+void dca_sysfs_remove_provider(struct dca_provider *dca)
+{
+	class_device_unregister(dca->cd);
+	dca->cd = NULL;
+	spin_lock(&dca_idr_lock);
+	idr_remove(&dca_idr, dca->id);
+	spin_unlock(&dca_idr_lock);
+}
+
+int __init dca_sysfs_init(void)
+{
+	idr_init(&dca_idr);
+	spin_lock_init(&dca_idr_lock);
+
+	dca_class = class_create(THIS_MODULE, "dca");
+	if (IS_ERR(dca_class)) {
+		idr_destroy(&dca_idr);
+		return PTR_ERR(dca_class);
+	}
+	return 0;
+}
+
+void __exit dca_sysfs_exit(void)
+{
+	class_destroy(dca_class);
+	idr_destroy(&dca_idr);
+}
+