linux-kernel - Re: [PATCH v2 1/1] usb: xhci: fix checking ep busy for CFC

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Date:	Thu, 29 Oct 2015 16:08:09 +0200
From:	Mathias Nyman <mathias.nyman@...ux.intel.com>
To:	"Lu, Baolu" <baolu.lu@...ux.intel.com>,
	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
	Mathias Nyman <mathias.nyman@...el.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/1] usb: xhci: fix checking ep busy for CFC

On 29.10.2015 14:58, Lu, Baolu wrote:
>
>
> On 10/29/2015 08:51 PM, Sergei Shtylyov wrote:
>> Hello.
>>
>> On 10/29/2015 5:46 AM, 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>
>>>
>>> ---
>>> v1->v2:
>>> Implement the logic in xhci_queue_isoc_tx_prepare() instead of
>>> a seperated function as suggested by Mathias.
>>>
>>> ---
>>>   drivers/usb/host/xhci-ring.c | 32 ++++++--------------------------
>>>   1 file changed, 6 insertions(+), 26 deletions(-)
>>>
>>> diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
>>> index fa83625..8edc286 100644
>>> --- a/drivers/usb/host/xhci-ring.c
>>> +++ b/drivers/usb/host/xhci-ring.c
>> [...]
>>> @@ -3983,10 +3961,12 @@ int xhci_queue_isoc_tx_prepare(struct xhci_hcd *xhci, gfp_t mem_flags,
>>>       }
>>>
>>>       /* Calculate the start frame and put it in urb->start_frame. */
>>> -    if (HCC_CFC(xhci->hcc_params) &&
>>> -            ep_ring_is_processing(xhci, slot_id, ep_index)) {
>>> -        urb->start_frame = xep->next_frame_id;
>>> -        goto skip_start_over;
>>> +    if (HCC_CFC(xhci->hcc_params)) {
>>> +        if ((le32_to_cpu(ep_ctx->ep_info) & EP_STATE_MASK)
>>> +                    == EP_STATE_RUNNING &&
>>> +                !list_empty(&ep_ring->td_list))
>>> +            urb->start_frame = xep->next_frame_id;
>>> +            goto skip_start_over;
>>
>>    Forgot {}?
>
> Oh, I am sorry. I am wondering how it passed my test.
>
> I will send v3 patch soon any way.
>
>

If you are anyway making a v3 then maybe one more change,
just for readability, no (real) functional change:

if (HCC_CFC(xhci->hcc_params) && !list_empty(&ep_ring->td_list)) {
   if (le32_to_cpu(ep_...

While thinking about code cleanup I also think we should use a local variable
u32 ep_info = le32_to_cpu(ep_ctx->ep_info) as it's used several times in xhci_queue_isoc_tx_preapare(),
causing a lot of line splitting.

It should be ok as we are under the same spinlock so ep_ctx should not change.

But that is not a fix sent to a rc and stable, I can make a separate cleanup patch for it later.

-Mathias
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