4 files changed, 35 insertions, 4 deletions

diff --git a/drivers/usb/host/xhci-hcd.c b/drivers/usb/host/xhci-hcd.c
index 816c39caca1c..994f4c0dda24 100644
--- a/drivers/usb/host/xhci-hcd.c
+++ b/drivers/usb/host/xhci-hcd.c
@@ -22,12 +22,18 @@
 
 #include <linux/irq.h>
 #include <linux/module.h>
+#include <linux/moduleparam.h>
 
 #include "xhci.h"
 
 #define DRIVER_AUTHOR "Sarah Sharp"
 #define DRIVER_DESC "'eXtensible' Host Controller (xHC) Driver"
 
+/* Some 0.95 hardware can't handle the chain bit on a Link TRB being cleared */
+static int link_quirk;
+module_param(link_quirk, int, S_IRUGO | S_IWUSR);
+MODULE_PARM_DESC(link_quirk, "Don't clear the chain bit on a link TRB");
+
 /* TODO: copied from ehci-hcd.c - can this be refactored? */
 /*
  * handshake - spin reading hc until handshake completes or fails
@@ -214,6 +220,12 @@ int xhci_init(struct usb_hcd *hcd)
 
         xhci_dbg(xhci, "xhci_init\n");
         spin_lock_init(&xhci->lock);
+        if (link_quirk) {
+                xhci_dbg(xhci, "QUIRK: Not clearing Link TRB chain bits.\n");
+                xhci->quirks |= XHCI_LINK_TRB_QUIRK;
+        } else {
+                xhci_dbg(xhci, "xHCI has no QUIRKS\n");
+        }
         retval = xhci_mem_init(xhci, GFP_KERNEL);
         xhci_dbg(xhci, "Finished xhci_init\n");
 
diff --git a/drivers/usb/host/xhci-mem.c b/drivers/usb/host/xhci-mem.c
index e6b9a1c6002d..cb2033879ae3 100644
--- a/drivers/usb/host/xhci-mem.c
+++ b/drivers/usb/host/xhci-mem.c
@@ -94,6 +94,9 @@ static void xhci_link_segments(struct xhci_hcd *xhci, struct xhci_segment *prev,
                 val = prev->trbs[TRBS_PER_SEGMENT-1].link.control;
                 val &= ~TRB_TYPE_BITMASK;
                 val |= TRB_TYPE(TRB_LINK);
+                /* Always set the chain bit with 0.95 hardware */
+                if (xhci_link_trb_quirk(xhci))
+                        val |= TRB_CHAIN;
                 prev->trbs[TRBS_PER_SEGMENT-1].link.control = val;
         }
         xhci_dbg(xhci, "Linking segment 0x%llx to segment 0x%llx (DMA)\n",
diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
index aa88a067148b..011458f4d9ce 100644
--- a/drivers/usb/host/xhci-ring.c
+++ b/drivers/usb/host/xhci-ring.c
@@ -172,8 +172,9 @@ static void inc_deq(struct xhci_hcd *xhci, struct xhci_ring *ring, bool consumer
  * have their chain bit cleared (so that each Link TRB is a separate TD).
  *
  * Section 6.4.4.1 of the 0.95 spec says link TRBs cannot have the chain bit
- * set, but other sections talk about dealing with the chain bit set.
- * Assume section 6.4.4.1 is wrong, and the chain bit can be set in a Link TRB.
+ * set, but other sections talk about dealing with the chain bit set.  This was
+ * fixed in the 0.96 specification errata, but we have to assume that all 0.95
+ * xHCI hardware can't handle the chain bit being cleared on a link TRB.
  */
 static void inc_enq(struct xhci_hcd *xhci, struct xhci_ring *ring, bool consumer)
 {
@@ -191,8 +192,14 @@ static void inc_enq(struct xhci_hcd *xhci, struct xhci_ring *ring, bool consumer
         while (last_trb(xhci, ring, ring->enq_seg, next)) {
                 if (!consumer) {
                         if (ring != xhci->event_ring) {
-                                next->link.control &= ~TRB_CHAIN;
-                                next->link.control |= chain;
+                                /* If we're not dealing with 0.95 hardware,
+                                 * carry over the chain bit of the previous TRB
+                                 * (which may mean the chain bit is cleared).
+                                 */
+                                if (!xhci_link_trb_quirk(xhci)) {
+                                        next->link.control &= ~TRB_CHAIN;
+                                        next->link.control |= chain;
+                                }
                                 /* Give this link TRB to the hardware */
                                 wmb();
                                 if (next->link.control & TRB_CYCLE)
diff --git a/drivers/usb/host/xhci.h b/drivers/usb/host/xhci.h
index ffe1625d4e1b..79ea627e8b8a 100644
--- a/drivers/usb/host/xhci.h
+++ b/drivers/usb/host/xhci.h
@@ -1058,6 +1058,8 @@ struct xhci_hcd {
         int                     noops_submitted;
         int                     noops_handled;
         int                     error_bitmask;
+        unsigned int            quirks;
+#define XHCI_LINK_TRB_QUIRK     (1 << 0)
 };
 
 /* For testing purposes */
@@ -1136,6 +1138,13 @@ static inline void xhci_write_64(struct xhci_hcd *xhci,
         writel(val_hi, ptr + 1);
 }
 
+static inline int xhci_link_trb_quirk(struct xhci_hcd *xhci)
+{
+        u32 temp = xhci_readl(xhci, &xhci->cap_regs->hc_capbase);
+        return ((HC_VERSION(temp) == 0x95) &&
+                        (xhci->quirks & XHCI_LINK_TRB_QUIRK));
+}
+
 /* xHCI debugging */
 void xhci_print_ir_set(struct xhci_hcd *xhci, struct xhci_intr_reg *ir_set, int set_num);
 void xhci_print_registers(struct xhci_hcd *xhci);