3 files changed, 94 insertions, 18 deletions

diff --git a/drivers/usb/host/xhci-hcd.c b/drivers/usb/host/xhci-hcd.c
index 0d5a8564ed17..5e92c72df642 100644
--- a/drivers/usb/host/xhci-hcd.c
+++ b/drivers/usb/host/xhci-hcd.c
@@ -1262,13 +1262,35 @@ int xhci_check_bandwidth(struct usb_hcd *hcd, struct usb_device *udev)
                         LAST_CTX_TO_EP_NUM(slot_ctx->dev_info));
 
         xhci_zero_in_ctx(xhci, virt_dev);
-        /* Free any old rings */
+        /* Install new rings and free or cache any old rings */
         for (i = 1; i < 31; ++i) {
-                if (virt_dev->eps[i].new_ring) {
-                        xhci_ring_free(xhci, virt_dev->eps[i].ring);
-                        virt_dev->eps[i].ring = virt_dev->eps[i].new_ring;
-                        virt_dev->eps[i].new_ring = NULL;
+                int rings_cached;
+
+                if (!virt_dev->eps[i].new_ring)
+                        continue;
+                /* Only cache or free the old ring if it exists.
+                 * It may not if this is the first add of an endpoint.
+                 */
+                if (virt_dev->eps[i].ring) {
+                        rings_cached = virt_dev->num_rings_cached;
+                        if (rings_cached < XHCI_MAX_RINGS_CACHED) {
+                                virt_dev->num_rings_cached++;
+                                rings_cached = virt_dev->num_rings_cached;
+                                virt_dev->ring_cache[rings_cached] =
+                                        virt_dev->eps[i].ring;
+                                xhci_dbg(xhci, "Cached old ring, "
+                                                "%d ring%s cached\n",
+                                                rings_cached,
+                                                (rings_cached > 1) ? "s" : "");
+                        } else {
+                                xhci_ring_free(xhci, virt_dev->eps[i].ring);
+                                xhci_dbg(xhci, "Ring cache full (%d rings), "
+                                                "freeing ring\n",
+                                                virt_dev->num_rings_cached);
+                        }
                 }
+                virt_dev->eps[i].ring = virt_dev->eps[i].new_ring;
+                virt_dev->eps[i].new_ring = NULL;
         }
 
         return ret;
diff --git a/drivers/usb/host/xhci-mem.c b/drivers/usb/host/xhci-mem.c
index 9034721106d7..bffcef7a5545 100644
--- a/drivers/usb/host/xhci-mem.c
+++ b/drivers/usb/host/xhci-mem.c
@@ -125,6 +125,23 @@ void xhci_ring_free(struct xhci_hcd *xhci, struct xhci_ring *ring)
         kfree(ring);
 }
 
+static void xhci_initialize_ring_info(struct xhci_ring *ring)
+{
+        /* The ring is empty, so the enqueue pointer == dequeue pointer */
+        ring->enqueue = ring->first_seg->trbs;
+        ring->enq_seg = ring->first_seg;
+        ring->dequeue = ring->enqueue;
+        ring->deq_seg = ring->first_seg;
+        /* The ring is initialized to 0. The producer must write 1 to the cycle
+         * bit to handover ownership of the TRB, so PCS = 1.  The consumer must
+         * compare CCS to the cycle bit to check ownership, so CCS = 1.
+         */
+        ring->cycle_state = 1;
+        /* Not necessary for new rings, but needed for re-initialized rings */
+        ring->enq_updates = 0;
+        ring->deq_updates = 0;
+}
+
 /**
  * Create a new ring with zero or more segments.
  *
@@ -173,17 +190,7 @@ static struct xhci_ring *xhci_ring_alloc(struct xhci_hcd *xhci,
                                 " segment %p (virtual), 0x%llx (DMA)\n",
                                 prev, (unsigned long long)prev->dma);
         }
-        /* The ring is empty, so the enqueue pointer == dequeue pointer */
-        ring->enqueue = ring->first_seg->trbs;
-        ring->enq_seg = ring->first_seg;
-        ring->dequeue = ring->enqueue;
-        ring->deq_seg = ring->first_seg;
-        /* The ring is initialized to 0. The producer must write 1 to the cycle
-         * bit to handover ownership of the TRB, so PCS = 1.  The consumer must
-         * compare CCS to the cycle bit to check ownership, so CCS = 1.
-         */
-        ring->cycle_state = 1;
-
+        xhci_initialize_ring_info(ring);
         return ring;
 
 fail:
@@ -191,6 +198,27 @@ fail:
         return 0;
 }
 
+/* Zero an endpoint ring (except for link TRBs) and move the enqueue and dequeue
+ * pointers to the beginning of the ring.
+ */
+static void xhci_reinit_cached_ring(struct xhci_hcd *xhci,
+                struct xhci_ring *ring)
+{
+        struct xhci_segment     *seg = ring->first_seg;
+        do {
+                memset(seg->trbs, 0,
+                                sizeof(union xhci_trb)*TRBS_PER_SEGMENT);
+                /* All endpoint rings have link TRBs */
+                xhci_link_segments(xhci, seg, seg->next, 1);
+                seg = seg->next;
+        } while (seg != ring->first_seg);
+        xhci_initialize_ring_info(ring);
+        /* td list should be empty since all URBs have been cancelled,
+         * but just in case...
+         */
+        INIT_LIST_HEAD(&ring->td_list);
+}
+
 #define CTX_SIZE(_hcc) (HCC_64BYTE_CONTEXT(_hcc) ? 64 : 32)
 
 struct xhci_container_ctx *xhci_alloc_container_ctx(struct xhci_hcd *xhci,
@@ -276,6 +304,12 @@ void xhci_free_virt_device(struct xhci_hcd *xhci, int slot_id)
                 if (dev->eps[i].ring)
                         xhci_ring_free(xhci, dev->eps[i].ring);
 
+        if (dev->ring_cache) {
+                for (i = 0; i < dev->num_rings_cached; i++)
+                        xhci_ring_free(xhci, dev->ring_cache[i]);
+                kfree(dev->ring_cache);
+        }
+
         if (dev->in_ctx)
                 xhci_free_container_ctx(xhci, dev->in_ctx);
         if (dev->out_ctx)
@@ -329,6 +363,14 @@ int xhci_alloc_virt_device(struct xhci_hcd *xhci, int slot_id,
         if (!dev->eps[0].ring)
                 goto fail;
 
+        /* Allocate pointers to the ring cache */
+        dev->ring_cache = kzalloc(
+                        sizeof(struct xhci_ring *)*XHCI_MAX_RINGS_CACHED,
+                        flags);
+        if (!dev->ring_cache)
+                goto fail;
+        dev->num_rings_cached = 0;
+
         init_completion(&dev->cmd_completion);
         INIT_LIST_HEAD(&dev->cmd_list);
 
@@ -555,8 +597,16 @@ int xhci_endpoint_init(struct xhci_hcd *xhci,
         /* Set up the endpoint ring */
         virt_dev->eps[ep_index].new_ring =
                 xhci_ring_alloc(xhci, 1, true, mem_flags);
-        if (!virt_dev->eps[ep_index].new_ring)
-                return -ENOMEM;
+        if (!virt_dev->eps[ep_index].new_ring) {
+                /* Attempt to use the ring cache */
+                if (virt_dev->num_rings_cached == 0)
+                        return -ENOMEM;
+                virt_dev->eps[ep_index].new_ring =
+                        virt_dev->ring_cache[virt_dev->num_rings_cached];
+                virt_dev->ring_cache[virt_dev->num_rings_cached] = NULL;
+                virt_dev->num_rings_cached--;
+                xhci_reinit_cached_ring(xhci, virt_dev->eps[ep_index].new_ring);
+        }
         ep_ring = virt_dev->eps[ep_index].new_ring;
         ep_ctx->deq = ep_ring->first_seg->dma | ep_ring->cycle_state;
 
diff --git a/drivers/usb/host/xhci.h b/drivers/usb/host/xhci.h
index bb8e6656cca4..877813505ef2 100644
--- a/drivers/usb/host/xhci.h
+++ b/drivers/usb/host/xhci.h
@@ -677,6 +677,10 @@ struct xhci_virt_device {
         struct xhci_container_ctx       *out_ctx;
         /* Used for addressing devices and configuration changes */
         struct xhci_container_ctx       *in_ctx;
+        /* Rings saved to ensure old alt settings can be re-instated */
+        struct xhci_ring                **ring_cache;
+        int                             num_rings_cached;
+#define XHCI_MAX_RINGS_CACHED   31
         struct xhci_virt_ep             eps[31];
         struct completion               cmd_completion;
         /* Status of the last command issued for this device */