linux-kernel - Re: [PATCH] usb: xhci: Workaround for erratum-A010129

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Date:   Fri, 21 Oct 2016 12:44:26 -0400 (EDT)
From:   Alan Stern <stern@...land.harvard.edu>
To:     Sriram Dash <sriram.dash@....com>
cc:     linux-kernel@...r.kernel.org, <linux-usb@...r.kernel.org>,
        <mathias.nyman@...el.com>, <gregkh@...uxfoundation.org>,
        <suresh.gupta@....com>, <felipe.balbi@...ux.intel.com>,
        Rajat Srivastava <rajat.srivastava@....com>,
        Rajesh Bhagat <rajesh.bhagat@....com>
Subject: Re: [PATCH] usb: xhci: Workaround for erratum-A010129

On Fri, 21 Oct 2016, Sriram Dash wrote:

> For the USB3.0 controller, USB 2.0 reset not driven while
> port is in Resume state. So, do not program the USB 2.0 reset
> (PORTSC[PR]=1) while in Resume state.
> 
> Signed-off-by: Rajat Srivastava <rajat.srivastava@....com>
> Signed-off-by: Sriram Dash <sriram.dash@....com>
> Signed-off-by: Rajesh Bhagat <rajesh.bhagat@....com>
> ---
>  drivers/usb/host/xhci-hub.c | 28 +++++++++++++++++++++++++++-
>  drivers/usb/host/xhci.h     |  1 +
>  2 files changed, 28 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/host/xhci-hub.c b/drivers/usb/host/xhci-hub.c
> index 730b9fd..3def0dd 100644
> --- a/drivers/usb/host/xhci-hub.c
> +++ b/drivers/usb/host/xhci-hub.c
> @@ -878,7 +878,7 @@ int xhci_hub_control(struct usb_hcd *hcd, u16 typeReq, u16 wValue,
>  	struct xhci_hcd	*xhci = hcd_to_xhci(hcd);
>  	int max_ports;
>  	unsigned long flags;
> -	u32 temp, status;
> +	u32 temp, status, tmp_status = 0;
>  	int retval = 0;
>  	__le32 __iomem **port_array;
>  	int slot_id;
> @@ -1098,6 +1098,32 @@ int xhci_hub_control(struct usb_hcd *hcd, u16 typeReq, u16 wValue,
>  			spin_lock_irqsave(&xhci->lock, flags);
>  			break;
>  		case USB_PORT_FEAT_RESET:
> +			/*
> +			 * Erratum : A010129
> +			 * Synopsys STAR 9000962562.
> +			 * USB 2.0 Reset Not Driven While Port in Resume
> +			 * While in USB 2.0 resume state (the PORTSC.PLS
> +			 * register bit is set to 4'd15), if the xHCI driver
> +			 * programs the PORTSC.PR register bit to 1, the
> +			 * controller does not drive a USB 2.0 reset
> +			 * and it does not generate a PORTSC.PRC=1 interrupt.
> +			 * So, The xHCI driver should not program a USB
> +			 * 2.0 reset (PORTSC.PR=1) while in resume
> +			 * (PORTSC.PLS=4'd15).
> +			 */
> +			if (xhci->quirks & XHCI_PORT_RST_ON_RESUME) {

It's always a bad idea to drive a reset signal while a port is 
resuming.  We don't need a quirk flag for this.  The HCD should never 
do it, and the USB core should never tell the HCD to do it.

Alan Stern