[U-Boot] [PATCH 2/2] [RFC] usb: ehci-hcd: Keep async schedule running

[Marek Vasut]

Profiling the EHCI driver shows a significant performance problem in
ehci_submit_async(). Specifically, this function keeps enabling and
disabling async schedule back and forth for every single transaction.
However, enabling/disabling the async schedule does not take effect
immediatelly, but instead may take up to 1 mS (8 uFrames) to complete.

This impacts USB storage significantly, esp. since the recent reduction
of maximum transfer size to support more USB storage devices. This in
turn results in sharp increase in the number of ehci_submit_async()
calls. Since one USB storage BBB transfer does three such calls and
the maximum transfer size is 120 kiB, the overhead is 6 mS per 120 kiB,
which is unacceptable.

However, this overhead can be removed simply by keeping the async
schedule running. Specifically, the first transfer starts the async
schedule and then each and every subsequent transfer only adds a new
QH into that schedule, waits until the QH is completed and does NOT
disable the async schedule. The async schedule is stopped only by
shutting down the controller, which must happen before moving out
of U-Boot, otherwise the controller will corrupt memory.

Signed-off-by: Marek Vasut <marek.vasut+renesas at gmail.com>
Cc: Bin Meng <bmeng.cn at gmail.com>
Cc: Simon Glass <sjg at chromium.org>
---
 drivers/usb/host/ehci-hcd.c | 51 +++++++++++++++----------------------
 1 file changed, 21 insertions(+), 30 deletions(-)

diff --git a/drivers/usb/host/ehci-hcd.c b/drivers/usb/host/ehci-hcd.c
index 61a61abb21..85918e85be 100644
--- a/drivers/usb/host/ehci-hcd.c
+++ b/drivers/usb/host/ehci-hcd.c
@@ -307,7 +307,7 @@ ehci_submit_async(struct usb_device *dev, unsigned long pipe, void *buffer,
 	volatile struct qTD *vtd;
 	unsigned long ts;
 	uint32_t *tdp;
-	uint32_t endpt, maxpacket, token, usbsts;
+	uint32_t endpt, maxpacket, token, usbsts, qhtoken;
 	uint32_t c, toggle;
 	uint32_t cmd;
 	int timeout;
@@ -551,22 +551,21 @@ ehci_submit_async(struct usb_device *dev, unsigned long pipe, void *buffer,
 	flush_dcache_range((unsigned long)qtd,
 			   ALIGN_END_ADDR(struct qTD, qtd, qtd_count));
 
-	/* Set async. queue head pointer. */
-	ehci_writel(&ctrl->hcor->or_asynclistaddr, virt_to_phys(&ctrl->qh_list));
-
 	usbsts = ehci_readl(&ctrl->hcor->or_usbsts);
 	ehci_writel(&ctrl->hcor->or_usbsts, (usbsts & 0x3f));
 
 	/* Enable async. schedule. */
 	cmd = ehci_readl(&ctrl->hcor->or_usbcmd);
-	cmd |= CMD_ASE;
-	ehci_writel(&ctrl->hcor->or_usbcmd, cmd);
+	if (!(cmd & CMD_ASE)) {
+		cmd |= CMD_ASE;
+		ehci_writel(&ctrl->hcor->or_usbcmd, cmd);
 
-	ret = handshake((uint32_t *)&ctrl->hcor->or_usbsts, STS_ASS, STS_ASS,
-			100 * 1000);
-	if (ret < 0) {
-		printf("EHCI fail timeout STS_ASS set\n");
-		goto fail;
+		ret = handshake((uint32_t *)&ctrl->hcor->or_usbsts, STS_ASS, STS_ASS,
+				100 * 1000);
+		if (ret < 0) {
+			printf("EHCI fail timeout STS_ASS set\n");
+			goto fail;
+		}
 	}
 
 	/* Wait for TDs to be processed. */
@@ -587,6 +586,11 @@ ehci_submit_async(struct usb_device *dev, unsigned long pipe, void *buffer,
 			break;
 		WATCHDOG_RESET();
 	} while (get_timer(ts) < timeout);
+	qhtoken = hc32_to_cpu(qh->qh_overlay.qt_token);
+
+	ctrl->qh_list.qh_link = cpu_to_hc32(virt_to_phys(&ctrl->qh_list) | QH_LINK_TYPE_QH);
+	flush_dcache_range((unsigned long)&ctrl->qh_list,
+		ALIGN_END_ADDR(struct QH, &ctrl->qh_list, 1));
 
 	/*
 	 * Invalidate the memory area occupied by buffer
@@ -605,25 +609,12 @@ ehci_submit_async(struct usb_device *dev, unsigned long pipe, void *buffer,
 	if (QT_TOKEN_GET_STATUS(token) & QT_TOKEN_STATUS_ACTIVE)
 		printf("EHCI timed out on TD - token=%#x\n", token);
 
-	/* Disable async schedule. */
-	cmd = ehci_readl(&ctrl->hcor->or_usbcmd);
-	cmd &= ~CMD_ASE;
-	ehci_writel(&ctrl->hcor->or_usbcmd, cmd);
-
-	ret = handshake((uint32_t *)&ctrl->hcor->or_usbsts, STS_ASS, 0,
-			100 * 1000);
-	if (ret < 0) {
-		printf("EHCI fail timeout STS_ASS reset\n");
-		goto fail;
-	}
-
-	token = hc32_to_cpu(qh->qh_overlay.qt_token);
-	if (!(QT_TOKEN_GET_STATUS(token) & QT_TOKEN_STATUS_ACTIVE)) {
-		debug("TOKEN=%#x\n", token);
-		switch (QT_TOKEN_GET_STATUS(token) &
+	if (!(QT_TOKEN_GET_STATUS(qhtoken) & QT_TOKEN_STATUS_ACTIVE)) {
+		debug("TOKEN=%#x\n", qhtoken);
+		switch (QT_TOKEN_GET_STATUS(qhtoken) &
 			~(QT_TOKEN_STATUS_SPLITXSTATE | QT_TOKEN_STATUS_PERR)) {
 		case 0:
-			toggle = QT_TOKEN_GET_DT(token);
+			toggle = QT_TOKEN_GET_DT(qhtoken);
 			usb_settoggle(dev, usb_pipeendpoint(pipe),
 				       usb_pipeout(pipe), toggle);
 			dev->status = 0;
@@ -641,11 +632,11 @@ ehci_submit_async(struct usb_device *dev, unsigned long pipe, void *buffer,
 			break;
 		default:
 			dev->status = USB_ST_CRC_ERR;
-			if (QT_TOKEN_GET_STATUS(token) & QT_TOKEN_STATUS_HALTED)
+			if (QT_TOKEN_GET_STATUS(qhtoken) & QT_TOKEN_STATUS_HALTED)
 				dev->status |= USB_ST_STALLED;
 			break;
 		}
-		dev->act_len = length - QT_TOKEN_GET_TOTALBYTES(token);
+		dev->act_len = length - QT_TOKEN_GET_TOTALBYTES(qhtoken);
 	} else {
 		dev->act_len = 0;
 #ifndef CONFIG_USB_EHCI_FARADAY
-- 
2.23.0