linux-kernel - Re: [PATCH 1/2] usb: host: Implement workaround for Erratum A-009611

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Date:   Mon, 11 Sep 2017 05:06:31 -0700
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     yinbo.zhu@....com
Cc:     Mathias Nyman <mathias.nyman@...el.com>,
        "open list:USB XHCI DRIVER" <linux-usb@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] usb: host: Implement workaround for Erratum A-009611

On Mon, Sep 11, 2017 at 05:41:32PM +0800, yinbo.zhu@....com wrote:
> From: "yinbo.zhu" <yinbo.zhu@....com>

Please use your "real" name in the from portion, I don't think you have
a "." in your name, right?  :)

And what hardware is this erratum for?  Please put that in the subject
line as well, as well as xhci, otherwise it is very vague.

> 
> Description: This is a occasional problem where the software

No need for "Description:" in a changelog text, the whole thing is a
description.

> issues an End Transfer command while a USB transfer is in progress,
> resulting in the TxFIFO  being flushed when the lower layer is waiting
> for data,causing the super speed (SS) transmit to get blocked.
> If the End Transfer command is issued on an IN endpoint to
> flush out the pending transfers when the same IN endpoint
> is doing transfers on the USB, then depending upon the timing
> of the End Transfer (and the resulting internal FIFO flush),the
> lower layer (U3PTL/U3MAC) could get stuck waiting for data
> indefinitely. This blocks the transmission path on the SS, and no
> DP/ACK/ERDY/DEVNOTIF packets can be sent from the device.
> Impact: If this issue happens and the transmission gets blocked,
> then the USB host aborts and resets/re-enumerates the device.
> This unblocks the transmitt engine and the device functions normally.
> 
> Workaround: Software must wait for all existing TRBs to complete before
> issuing End transfer command.
> 
> Signed-off-by: yinbo.zhu <yinbo.zhu@....com>
> ---
>  drivers/usb/host/xhci.c | 23 ++++++++++++++++-------
>  1 file changed, 16 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c
> index 2d6a98c1dc12..35f7821bc8b2 100644
> --- a/drivers/usb/host/xhci.c
> +++ b/drivers/usb/host/xhci.c
> @@ -1501,13 +1501,22 @@ static int xhci_urb_dequeue(struct usb_hcd *hcd, struct urb *urb, int status)
>  			ret = -ENOMEM;
>  			goto done;
>  		}
> -		ep->ep_state |= EP_STOP_CMD_PENDING;
> -		ep->stop_cmd_timer.expires = jiffies +
> -			XHCI_STOP_EP_CMD_TIMEOUT * HZ;
> -		add_timer(&ep->stop_cmd_timer);
> -		xhci_queue_stop_endpoint(xhci, command, urb->dev->slot_id,
> -					 ep_index, 0);
> -		xhci_ring_cmd_db(xhci);
> +
> +		/*
> +		 *A-009611: Issuing an End Transfer command on an IN endpoint.
> +		 *when a transfer is in progress on USB blocks the transmission
> +		 *Workaround: Software must wait for all existing TRBs to
> +		 *complete before issuing End transfer command.
> +		 */

Please properly format your comments.

And what is the A-009611: for?

And is this really for all xhci controllers?

> +		if (ep_ring->enqueue == ep_ring->dequeue) {
> +			ep->ep_state |= EP_STOP_CMD_PENDING;
> +			ep->stop_cmd_timer.expires = jiffies +
> +				XHCI_STOP_EP_CMD_TIMEOUT * HZ;
> +			add_timer(&ep->stop_cmd_timer);
> +			xhci_queue_stop_endpoint(xhci, command,
> +			urb->dev->slot_id, ep_index, 0);
> +			xhci_ring_cmd_db(xhci);
> +		}
>  	}


thanks,

greg k-h