[PATCH v2] ehci: fix EHCI host controller initialization sequence

[PATCH v2] ehci: fix EHCI host controller initialization sequence

[Eugene Korenevsky]

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.

Instead, previous version of ehci_run() wrote 1 to USBCMD.RS, issued read to
USBCMD and waited for 5 ms.
That worked incorrectly at least for VirtualBox's EHCI virtual HC and caused
accidental hangs.

BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=211095 
Signed-off-by: Eugene Korenevsky <ekorenevsky@astralinux.ru>
---
 drivers/usb/host/ehci-hcd.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/host/ehci-hcd.c b/drivers/usb/host/ehci-hcd.c
index e358ae17d51e..490473af4906 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 +630,18 @@ 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);
-	ehci_readl(ehci, &ehci->regs->command);	/* unblock posted writes */
-	msleep(5);
+
+	/* Wait until HCD become operational */
+	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, handshake error: %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

Re: [PATCH v2] ehci: fix EHCI host controller initialization sequence

[Alan Stern]

On Sat, Jan 09, 2021 at 05:47:36PM +0300, Eugene Korenevsky wrote:
> 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.
> 
> Instead, previous version of ehci_run() wrote 1 to USBCMD.RS, issued read to
> USBCMD and waited for 5 ms.
> That worked incorrectly at least for VirtualBox's EHCI virtual HC and caused
> accidental hangs.
> 
> BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=211095 
> Signed-off-by: Eugene Korenevsky <ekorenevsky@astralinux.ru>
> ---
>  drivers/usb/host/ehci-hcd.c | 14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/usb/host/ehci-hcd.c b/drivers/usb/host/ehci-hcd.c
> index e358ae17d51e..490473af4906 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 +630,18 @@ 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);
> -	ehci_readl(ehci, &ehci->regs->command);	/* unblock posted writes */
> -	msleep(5);
> +
> +	/* Wait until HCD become operational */
> +	rc = ehci_handshake(ehci, &ehci->regs->status, STS_HALT, 0, 100 * 1000);
> +
>  	up_write(&ehci_cf_port_reset_rwsem);

Are you sure you don't want to wait 5 ms before polling the STS_HALT 
flag?  It would use less CPU time and should suffice in the majority of 
cases.

> +
> +	if (rc) {
> +		ehci_err(ehci, "USB %x.%x, handshake error: %d\n",
> +			 ((ehci->sbrn & 0xf0)>>4), (ehci->sbrn & 0x0f), rc);

How about something a little less generic than "handshake error"?  Like 
"controller refused to start"?

Alan Stern

> +		return rc;
> +	}
> +
>  	ehci->last_periodic_enable = ktime_get_real();
>  
>  	temp = HC_VERSION(ehci, ehci_readl(ehci, &ehci->caps->hc_capbase));
> -- 
> 2.20.1
>