linux-kernel - Re: [PATCH 1/1] usb: xhci: fix checking ep busy for CFC

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Date:	Wed, 28 Oct 2015 15:27:10 +0200
From:	Mathias Nyman <mathias.nyman@...el.com>
To:	Lu Baolu <baolu.lu@...ux.intel.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] usb: xhci: fix checking ep busy for CFC

On 28.10.2015 03:36, Lu Baolu wrote:
> Function ep_ring_is_processing() checks the dequeue pointer
> in endpoint context to know whether an endpoint is busy with
> processing TRBs. This is not correct since dequeue pointer
> field in an endpoint context is only valid when the endpoint
> is in Halted or Stopped states. This buggy code causes audio
> noise when playing sound with USB headset connected to host
> controllers which support CFC (one of xhci 1.1 features).
>
> This patch should exist in stable kernel since v4.3.
>
> Reported-and-tested-by: YD Tseng <yd_tseng@...edia.com.tw>
> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
> ---
>   drivers/usb/host/xhci-ring.c | 5 +----
>   1 file changed, 1 insertion(+), 4 deletions(-)
>
> diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
> index fa83625..2b50d45 100644
> --- a/drivers/usb/host/xhci-ring.c
> +++ b/drivers/usb/host/xhci-ring.c
> @@ -3903,7 +3903,6 @@ static int ep_ring_is_processing(struct xhci_hcd *xhci,
>   	struct xhci_ring *ep_ring;
>   	struct xhci_ep_ctx *ep_ctx;
>   	struct xhci_virt_ep *xep;
> -	dma_addr_t hw_deq;
>
>   	xdev = xhci->devs[slot_id];
>   	xep = &xhci->devs[slot_id]->eps[ep_index];
> @@ -3913,9 +3912,7 @@ static int ep_ring_is_processing(struct xhci_hcd *xhci,
>   	if ((le32_to_cpu(ep_ctx->ep_info) & EP_STATE_MASK) != EP_STATE_RUNNING)
>   		return 0;
>
> -	hw_deq = le64_to_cpu(ep_ctx->deq) & ~EP_CTX_CYCLE_MASK;
> -	return (hw_deq !=
> -		xhci_trb_virt_to_dma(ep_ring->enq_seg, ep_ring->enqueue));
> +	return !list_empty(&ep_ring->td_list);
>   }

Would it make sense to remove the ep_ring_is_processing() function completely?

It is only called in one place, and the main use is checking list_empty(&ep_ring->td_list).
This could be checked directly in xhci_queue_isoc_tx_prepare()

-Mathias

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