[PATCH] ehci: add think_time

This adds think_time to the usb_tt struct and sets it appropriately
(measured in ns); this can help us implement better split transaction
scheduling.

Signed-off-by: Dan Streetman <ddstreet@ieee.org>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

2 files changed, 30 insertions, 9 deletions

diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index 9f54e8330f78..758c7f0ed159 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -627,19 +627,33 @@ static int hub_configure(struct usb_hub *hub,
                         break;
         }
 
+        /* Note 8 FS bit times == (8 bits / 12000000 bps) ~= 666ns */
         switch (hub->descriptor->wHubCharacteristics & HUB_CHAR_TTTT) {
-                case 0x00:
-                        if (hdev->descriptor.bDeviceProtocol != 0)
-                                dev_dbg(hub_dev, "TT requires at most 8 FS bit times\n");
+                case HUB_TTTT_8_BITS:
+                        if (hdev->descriptor.bDeviceProtocol != 0) {
+                                hub->tt.think_time = 666;
+                                dev_dbg(hub_dev, "TT requires at most %d "
+                                                "FS bit times (%d ns)\n",
+                                        8, hub->tt.think_time);
+                        }
                         break;
-                case 0x20:
-                        dev_dbg(hub_dev, "TT requires at most 16 FS bit times\n");
+                case HUB_TTTT_16_BITS:
+                        hub->tt.think_time = 666 * 2;
+                        dev_dbg(hub_dev, "TT requires at most %d "
+                                        "FS bit times (%d ns)\n",
+                                16, hub->tt.think_time);
                         break;
-                case 0x40:
-                        dev_dbg(hub_dev, "TT requires at most 24 FS bit times\n");
+                case HUB_TTTT_24_BITS:
+                        hub->tt.think_time = 666 * 3;
+                        dev_dbg(hub_dev, "TT requires at most %d "
+                                        "FS bit times (%d ns)\n",
+                                24, hub->tt.think_time);
                         break;
-                case 0x60:
-                        dev_dbg(hub_dev, "TT requires at most 32 FS bit times\n");
+                case HUB_TTTT_32_BITS:
+                        hub->tt.think_time = 666 * 4;
+                        dev_dbg(hub_dev, "TT requires at most %d "
+                                        "FS bit times (%d ns)\n",
+                                32, hub->tt.think_time);
                         break;
         }
 
diff --git a/drivers/usb/core/hub.h b/drivers/usb/core/hub.h
index 53bf5649621e..e7fa9b5a521e 100644
--- a/drivers/usb/core/hub.h
+++ b/drivers/usb/core/hub.h
@@ -157,6 +157,12 @@ enum hub_led_mode {
 
 struct usb_device;
 
+/* Transaction Translator Think Times, in bits */
+#define HUB_TTTT_8_BITS         0x00
+#define HUB_TTTT_16_BITS        0x20
+#define HUB_TTTT_24_BITS        0x40
+#define HUB_TTTT_32_BITS        0x60
+
 /*
  * As of USB 2.0, full/low speed devices are segregated into trees.
  * One type grows from USB 1.1 host controllers (OHCI, UHCI etc).
@@ -170,6 +176,7 @@ struct usb_device;
 struct usb_tt {
         struct usb_device       *hub;   /* upstream highspeed hub */
         int                     multi;  /* true means one TT per port */
+        unsigned                think_time;     /* think time in ns */
 
         /* for control/bulk error recovery (CLEAR_TT_BUFFER) */
         spinlock_t              lock;