[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>

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;
 	}
 

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;