EHCI: workaround for MosChip controller bug

This patch (as1489) works around a hardware bug in MosChip EHCI
controllers.  Evidently when one of these controllers increments the
frame-index register, it changes the three low-order bits (the
microframe counter) before changing the higher order bits (the frame
counter).  If the register is read at just the wrong time, the value
obtained is too low by 8.

When the appropriate quirk flag is set, we work around this problem by
reading the frame-index register a second time if the first value's
three low-order bits are all 0.  This gives the hardware a chance to
finish updating the register, yielding the correct value.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Tested-by: Jason N Pitt <jpitt@fhcrc.org>
CC: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

5 files changed, 49 insertions, 8 deletions

diff --git a/drivers/usb/host/ehci-dbg.c b/drivers/usb/host/ehci-dbg.c
index 9952505d2357..d6d74d2e09f4 100644
--- a/drivers/usb/host/ehci-dbg.c
+++ b/drivers/usb/host/ehci-dbg.c
@@ -821,7 +821,7 @@ static ssize_t fill_registers_buffer(struct debug_buffer *buf)
         next += temp;
 
         temp = scnprintf (next, size, "uframe %04x\n",
-                        ehci_readl(ehci, &ehci->regs->frame_index));
+                        ehci_read_frame_index(ehci));
         size -= temp;
         next += temp;
 
diff --git a/drivers/usb/host/ehci-hcd.c b/drivers/usb/host/ehci-hcd.c
index 05abbcd93cf4..59e81615e09c 100644
--- a/drivers/usb/host/ehci-hcd.c
+++ b/drivers/usb/host/ehci-hcd.c
@@ -1195,8 +1195,7 @@ ehci_endpoint_reset(struct usb_hcd *hcd, struct usb_host_endpoint *ep)
 static int ehci_get_frame (struct usb_hcd *hcd)
 {
         struct ehci_hcd         *ehci = hcd_to_ehci (hcd);
-        return (ehci_readl(ehci, &ehci->regs->frame_index) >> 3) %
-                ehci->periodic_size;
+        return (ehci_read_frame_index(ehci) >> 3) % ehci->periodic_size;
 }
 
 /*-------------------------------------------------------------------------*/
diff --git a/drivers/usb/host/ehci-pci.c b/drivers/usb/host/ehci-pci.c
index 8311de7c0a75..f4b627d343ac 100644
--- a/drivers/usb/host/ehci-pci.c
+++ b/drivers/usb/host/ehci-pci.c
@@ -224,6 +224,11 @@ static int ehci_pci_setup(struct usb_hcd *hcd)
                         pci_dev_put(p_smbus);
                 }
                 break;
+        case PCI_VENDOR_ID_NETMOS:
+                /* MosChip frame-index-register bug */
+                ehci_info(ehci, "applying MosChip frame-index workaround\n");
+                ehci->frame_index_bug = 1;
+                break;
         }
 
         /* optional debug port, normally in the first BAR */
diff --git a/drivers/usb/host/ehci-sched.c b/drivers/usb/host/ehci-sched.c
index 488151bb45cb..2e829fae6482 100644
--- a/drivers/usb/host/ehci-sched.c
+++ b/drivers/usb/host/ehci-sched.c
@@ -36,6 +36,27 @@
 
 static int ehci_get_frame (struct usb_hcd *hcd);
 
+#ifdef CONFIG_PCI
+
+static unsigned ehci_read_frame_index(struct ehci_hcd *ehci)
+{
+        unsigned uf;
+
+        /*
+         * The MosChip MCS9990 controller updates its microframe counter
+         * a little before the frame counter, and occasionally we will read
+         * the invalid intermediate value.  Avoid problems by checking the
+         * microframe number (the low-order 3 bits); if they are 0 then
+         * re-read the register to get the correct value.
+         */
+        uf = ehci_readl(ehci, &ehci->regs->frame_index);
+        if (unlikely(ehci->frame_index_bug && ((uf & 7) == 0)))
+                uf = ehci_readl(ehci, &ehci->regs->frame_index);
+        return uf;
+}
+
+#endif
+
 /*-------------------------------------------------------------------------*/
 
 /*
@@ -481,7 +502,7 @@ static int enable_periodic (struct ehci_hcd *ehci)
         /* posted write ... PSS happens later */
 
         /* make sure ehci_work scans these */
-        ehci->next_uframe = ehci_readl(ehci, &ehci->regs->frame_index)
+        ehci->next_uframe = ehci_read_frame_index(ehci)
                 % (ehci->periodic_size << 3);
         if (unlikely(ehci->broken_periodic))
                 ehci->last_periodic_enable = ktime_get_real();
@@ -1408,7 +1429,7 @@ iso_stream_schedule (
                 goto fail;
         }
 
-        now = ehci_readl(ehci, &ehci->regs->frame_index) & (mod - 1);
+        now = ehci_read_frame_index(ehci) & (mod - 1);
 
         /* Typical case: reuse current schedule, stream is still active.
          * Hopefully there are no gaps from the host falling behind
@@ -2275,7 +2296,7 @@ scan_periodic (struct ehci_hcd *ehci)
          */
         now_uframe = ehci->next_uframe;
         if (ehci->rh_state == EHCI_RH_RUNNING) {
-                clock = ehci_readl(ehci, &ehci->regs->frame_index);
+                clock = ehci_read_frame_index(ehci);
                 clock_frame = (clock >> 3) & (ehci->periodic_size - 1);
         } else  {
                 clock = now_uframe + mod - 1;
@@ -2454,8 +2475,7 @@ restart:
                                         || ehci->periodic_sched == 0)
                                 break;
                         ehci->next_uframe = now_uframe;
-                        now = ehci_readl(ehci, &ehci->regs->frame_index) &
-                                        (mod - 1);
+                        now = ehci_read_frame_index(ehci) & (mod - 1);
                         if (now_uframe == now)
                                 break;
 
diff --git a/drivers/usb/host/ehci.h b/drivers/usb/host/ehci.h
index c161d97de7dd..0a5fda73b3f2 100644
--- a/drivers/usb/host/ehci.h
+++ b/drivers/usb/host/ehci.h
@@ -146,6 +146,7 @@ struct ehci_hcd {			/* one per controller */
         unsigned                fs_i_thresh:1;  /* Intel iso scheduling */
         unsigned                use_dummy_qh:1; /* AMD Frame List table quirk*/
         unsigned                has_synopsys_hc_bug:1; /* Synopsys HC */
+        unsigned                frame_index_bug:1; /* MosChip (AKA NetMos) */
 
         /* required for usb32 quirk */
         #define OHCI_CTRL_HCFS          (3 << 6)
@@ -747,6 +748,22 @@ static inline u32 hc32_to_cpup (const struct ehci_hcd *ehci, const __hc32 *x)
 
 /*-------------------------------------------------------------------------*/
 
+#ifdef CONFIG_PCI
+
+/* For working around the MosChip frame-index-register bug */
+static unsigned ehci_read_frame_index(struct ehci_hcd *ehci);
+
+#else
+
+static inline unsigned ehci_read_frame_index(struct ehci_hcd *ehci)
+{
+        return ehci_readl(ehci, &ehci->regs->frame_index);
+}
+
+#endif
+
+/*-------------------------------------------------------------------------*/
+
 #ifndef DEBUG
 #define STUB_DEBUG_FILES
 #endif  /* DEBUG */