linux-kernel - [PATCH v6] ehci: fix EHCI host controller initialization sequence

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Message-ID: <20210110173609.GA17313@himera.home>
Date:   Sun, 10 Jan 2021 20:36:09 +0300
From:   Eugene Korenevsky <ekorenevsky@...ralinux.ru>
To:     linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Alan Stern <stern@...land.harvard.edu>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: [PATCH v6] ehci: fix EHCI host controller initialization sequence

According to EHCI spec, EHCI HC clears USBSTS.HCHalted whenever
USBCMD.RS=1.

However, it is a good practice to wait some time after setting USBCMD.RS
(approximately 100ms) until USBSTS.HCHalted become zero.

Without this waiting, VirtualBox's EHCI virtual HC accidentally hangs
(see BugLink).

BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=211095 
Acked-by: Alan Stern <stern@...land.harvard.edu>
Signed-off-by: Eugene Korenevsky <ekorenevsky@...ralinux.ru>
---
v1: initial patch
v2: add BugLink tag
v3: add Revieved-By tags (incorrect), restore `msleep(5)`
v4: remove Reviewed-By tags, restore reading from USBCMD prior to msleep,
adjust description
v5: add `patch changelog`
v6: add `Acked-by: Alan Stern <stern@...land.harvard.edu>` tag

 drivers/usb/host/ehci-hcd.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/usb/host/ehci-hcd.c b/drivers/usb/host/ehci-hcd.c
index e358ae17d51e..1926b328b6aa 100644
--- a/drivers/usb/host/ehci-hcd.c
+++ b/drivers/usb/host/ehci-hcd.c
@@ -574,6 +574,7 @@ static int ehci_run (struct usb_hcd *hcd)
 	struct ehci_hcd		*ehci = hcd_to_ehci (hcd);
 	u32			temp;
 	u32			hcc_params;
+	int			rc;
 
 	hcd->uses_new_polling = 1;
 
@@ -629,9 +630,20 @@ static int ehci_run (struct usb_hcd *hcd)
 	down_write(&ehci_cf_port_reset_rwsem);
 	ehci->rh_state = EHCI_RH_RUNNING;
 	ehci_writel(ehci, FLAG_CF, &ehci->regs->configured_flag);
+
+	/* Wait until HC become operational */
 	ehci_readl(ehci, &ehci->regs->command);	/* unblock posted writes */
 	msleep(5);
+	rc = ehci_handshake(ehci, &ehci->regs->status, STS_HALT, 0, 100 * 1000);
+
 	up_write(&ehci_cf_port_reset_rwsem);
+
+	if (rc) {
+		ehci_err(ehci, "USB %x.%x, controller refused to start: %d\n",
+			 ((ehci->sbrn & 0xf0)>>4), (ehci->sbrn & 0x0f), rc);
+		return rc;
+	}
+
 	ehci->last_periodic_enable = ktime_get_real();
 
 	temp = HC_VERSION(ehci, ehci_readl(ehci, &ehci->caps->hc_capbase));
-- 
2.20.1