[PATCH 14/17] drm/amdkfd: use standard kernel kfifo for IH

[Felix Kuehling]

From: Andres Rodriguez <andres.rodriguez at amd.com>

Replace our implementation of a lockless ring buffer with the standard
linux kernel kfifo.

We shouldn't maintain our own version of a standard data structure.

Signed-off-by: Andres Rodriguez <andres.rodriguez at amd.com>
Signed-off-by: Felix Kuehling <Felix.Kuehling at amd.com>
Acked-by: Oded Gabbay <oded.gabbay at gmail.com>
---
 drivers/gpu/drm/amd/amdkfd/kfd_interrupt.c | 78 ++++++++++--------------------
 drivers/gpu/drm/amd/amdkfd/kfd_priv.h      |  6 +--
 2 files changed, 27 insertions(+), 57 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_interrupt.c b/drivers/gpu/drm/amd/amdkfd/kfd_interrupt.c
index 70b3a99c..ffbb91a 100644
--- a/drivers/gpu/drm/amd/amdkfd/kfd_interrupt.c
+++ b/drivers/gpu/drm/amd/amdkfd/kfd_interrupt.c
@@ -42,25 +42,24 @@
 
 #include <linux/slab.h>
 #include <linux/device.h>
+#include <linux/kfifo.h>
 #include "kfd_priv.h"
 
-#define KFD_INTERRUPT_RING_SIZE 1024
+#define KFD_IH_NUM_ENTRIES 1024
 
 static void interrupt_wq(struct work_struct *);
 
 int kfd_interrupt_init(struct kfd_dev *kfd)
 {
-	void *interrupt_ring = kmalloc_array(KFD_INTERRUPT_RING_SIZE,
-					kfd->device_info->ih_ring_entry_size,
-					GFP_KERNEL);
-	if (!interrupt_ring)
-		return -ENOMEM;
-
-	kfd->interrupt_ring = interrupt_ring;
-	kfd->interrupt_ring_size =
-		KFD_INTERRUPT_RING_SIZE * kfd->device_info->ih_ring_entry_size;
-	atomic_set(&kfd->interrupt_ring_wptr, 0);
-	atomic_set(&kfd->interrupt_ring_rptr, 0);
+	int r;
+
+	r = kfifo_alloc(&kfd->ih_fifo,
+		KFD_IH_NUM_ENTRIES * kfd->device_info->ih_ring_entry_size,
+		GFP_KERNEL);
+	if (r) {
+		dev_err(kfd_chardev(), "Failed to allocate IH fifo\n");
+		return r;
+	}
 
 	spin_lock_init(&kfd->interrupt_lock);
 
@@ -98,68 +97,41 @@ void kfd_interrupt_exit(struct kfd_dev *kfd)
 	 */
 	flush_scheduled_work();
 
-	kfree(kfd->interrupt_ring);
+	kfifo_free(&kfd->ih_fifo);
 }
 
 /*
- * This assumes that it can't be called concurrently with itself
- * but only with dequeue_ih_ring_entry.
+ * Assumption: single reader/writer. This function is not re-entrant
  */
 bool enqueue_ih_ring_entry(struct kfd_dev *kfd,	const void *ih_ring_entry)
 {
-	unsigned int rptr = atomic_read(&kfd->interrupt_ring_rptr);
-	unsigned int wptr = atomic_read(&kfd->interrupt_ring_wptr);
+	int count;
 
-	if ((rptr - wptr) % kfd->interrupt_ring_size ==
-					kfd->device_info->ih_ring_entry_size) {
-		/* This is very bad, the system is likely to hang. */
+	count = kfifo_in(&kfd->ih_fifo, ih_ring_entry,
+				kfd->device_info->ih_ring_entry_size);
+	if (count != kfd->device_info->ih_ring_entry_size) {
 		dev_err_ratelimited(kfd_chardev(),
-			"Interrupt ring overflow, dropping interrupt.\n");
+			"Interrupt ring overflow, dropping interrupt %d\n",
+			count);
 		return false;
 	}
 
-	memcpy(kfd->interrupt_ring + wptr, ih_ring_entry,
-			kfd->device_info->ih_ring_entry_size);
-
-	wptr = (wptr + kfd->device_info->ih_ring_entry_size) %
-			kfd->interrupt_ring_size;
-	smp_wmb(); /* Ensure memcpy'd data is visible before wptr update. */
-	atomic_set(&kfd->interrupt_ring_wptr, wptr);
-
 	return true;
 }
 
 /*
- * This assumes that it can't be called concurrently with itself
- * but only with enqueue_ih_ring_entry.
+ * Assumption: single reader/writer. This function is not re-entrant
  */
 static bool dequeue_ih_ring_entry(struct kfd_dev *kfd, void *ih_ring_entry)
 {
-	/*
-	 * Assume that wait queues have an implicit barrier, i.e. anything that
-	 * happened in the ISR before it queued work is visible.
-	 */
-
-	unsigned int wptr = atomic_read(&kfd->interrupt_ring_wptr);
-	unsigned int rptr = atomic_read(&kfd->interrupt_ring_rptr);
+	int count;
 
-	if (rptr == wptr)
-		return false;
-
-	memcpy(ih_ring_entry, kfd->interrupt_ring + rptr,
-			kfd->device_info->ih_ring_entry_size);
-
-	rptr = (rptr + kfd->device_info->ih_ring_entry_size) %
-			kfd->interrupt_ring_size;
+	count = kfifo_out(&kfd->ih_fifo, ih_ring_entry,
+				kfd->device_info->ih_ring_entry_size);
 
-	/*
-	 * Ensure the rptr write update is not visible until
-	 * memcpy has finished reading.
-	 */
-	smp_mb();
-	atomic_set(&kfd->interrupt_ring_rptr, rptr);
+	WARN_ON(count && count != kfd->device_info->ih_ring_entry_size);
 
-	return true;
+	return count == kfd->device_info->ih_ring_entry_size;
 }
 
 static void interrupt_wq(struct work_struct *work)
diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_priv.h b/drivers/gpu/drm/amd/amdkfd/kfd_priv.h
index ba26da8..0aec5ca 100644
--- a/drivers/gpu/drm/amd/amdkfd/kfd_priv.h
+++ b/drivers/gpu/drm/amd/amdkfd/kfd_priv.h
@@ -32,6 +32,7 @@
 #include <linux/spinlock.h>
 #include <linux/kfd_ioctl.h>
 #include <linux/idr.h>
+#include <linux/kfifo.h>
 #include <kgd_kfd_interface.h>
 
 #include "amd_shared.h"
@@ -182,10 +183,7 @@ struct kfd_dev {
 	unsigned int gtt_sa_num_of_chunks;
 
 	/* Interrupts */
-	void *interrupt_ring;
-	size_t interrupt_ring_size;
-	atomic_t interrupt_ring_rptr;
-	atomic_t interrupt_ring_wptr;
+	struct kfifo ih_fifo;
 	struct work_struct interrupt_work;
 	spinlock_t interrupt_lock;
 
-- 
2.7.4