xhci: Remove more doorbell-related reads

The unused space in the doorbell is now marked as RsvdZ, not RsvdP, so
we can avoid reading the doorbell before writing it.

Update the doorbell-related defines to produce the entire doorbell value
from a single macro.  Document the doorbell format in a comment.

Signed-off-by: Matthew Wilcox <willy@linux.intel.com>
Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>

2 files changed, 17 insertions, 26 deletions

diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
index 2116c0f64952..3e8211c1ce5a 100644
--- a/drivers/usb/host/xhci-ring.c
+++ b/drivers/usb/host/xhci-ring.c
@@ -308,11 +308,8 @@ static int room_on_ring(struct xhci_hcd *xhci, struct xhci_ring *ring,
 /* Ring the host controller doorbell after placing a command on the ring */
 void xhci_ring_cmd_db(struct xhci_hcd *xhci)
 {
-        u32 temp;
-
         xhci_dbg(xhci, "// Ding dong!\n");
-        temp = xhci_readl(xhci, &xhci->dba->doorbell[0]) & DB_MASK;
-        xhci_writel(xhci, temp | DB_TARGET_HOST, &xhci->dba->doorbell[0]);
+        xhci_writel(xhci, DB_VALUE_HOST, &xhci->dba->doorbell[0]);
         /* Flush PCI posted writes */
         xhci_readl(xhci, &xhci->dba->doorbell[0]);
 }
@@ -322,26 +319,24 @@ void xhci_ring_ep_doorbell(struct xhci_hcd *xhci,
                 unsigned int ep_index,
                 unsigned int stream_id)
 {
-        struct xhci_virt_ep *ep;
-        unsigned int ep_state;
-        u32 field;
         __u32 __iomem *db_addr = &xhci->dba->doorbell[slot_id];
+        struct xhci_virt_ep *ep = &xhci->devs[slot_id]->eps[ep_index];
+        unsigned int ep_state = ep->ep_state;
 
-        ep = &xhci->devs[slot_id]->eps[ep_index];
-        ep_state = ep->ep_state;
         /* Don't ring the doorbell for this endpoint if there are pending
-         * cancellations because the we don't want to interrupt processing.
+         * cancellations because we don't want to interrupt processing.
          * We don't want to restart any stream rings if there's a set dequeue
          * pointer command pending because the device can choose to start any
          * stream once the endpoint is on the HW schedule.
          * FIXME - check all the stream rings for pending cancellations.
          */
-        if (!(ep_state & EP_HALT_PENDING) && !(ep_state & SET_DEQ_PENDING)
-                        && !(ep_state & EP_HALTED)) {
-                field = xhci_readl(xhci, db_addr) & DB_MASK;
-                field |= EPI_TO_DB(ep_index) | STREAM_ID_TO_DB(stream_id);
-                xhci_writel(xhci, field, db_addr);
-        }
+        if ((ep_state & EP_HALT_PENDING) || (ep_state & SET_DEQ_PENDING) ||
+            (ep_state & EP_HALTED))
+                return;
+        xhci_writel(xhci, DB_VALUE(ep_index, stream_id), db_addr);
+        /* The CPU has better things to do at this point than wait for a
+         * write-posting flush.  It'll get there soon enough.
+         */
 }
 
 /* Ring the doorbell for any rings with pending URBs */
diff --git a/drivers/usb/host/xhci.h b/drivers/usb/host/xhci.h
index 170c367112d2..7f236fd22015 100644
--- a/drivers/usb/host/xhci.h
+++ b/drivers/usb/host/xhci.h
@@ -436,22 +436,18 @@ struct xhci_run_regs {
 /**
  * struct doorbell_array
  *
+ * Bits  0 -  7: Endpoint target
+ * Bits  8 - 15: RsvdZ
+ * Bits 16 - 31: Stream ID
+ *
  * Section 5.6
  */
 struct xhci_doorbell_array {
         u32     doorbell[256];
 };
 
-#define DB_TARGET_MASK          0xFFFFFF00
-#define DB_STREAM_ID_MASK       0x0000FFFF
-#define DB_TARGET_HOST          0x0
-#define DB_STREAM_ID_HOST       0x0
-#define DB_MASK                 (0xff << 8)
-
-/* Endpoint Target - bits 0:7 */
-#define EPI_TO_DB(p)            (((p) + 1) & 0xff)
-#define STREAM_ID_TO_DB(p)      (((p) & 0xffff) << 16)
-
+#define DB_VALUE(ep, stream)    ((((ep) + 1) & 0xff) | ((stream) << 16))
+#define DB_VALUE_HOST           0x00000000
 
 /**
  * struct xhci_protocol_caps