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

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Message-ID: <56322C46.4060800@linux.intel.com>
Date:	Thu, 29 Oct 2015 22:25:10 +0800
From:	"Lu, Baolu" <baolu.lu@...ux.intel.com>
To:	Mathias Nyman <mathias.nyman@...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 10/29/2015 10:08 PM, Mathias Nyman wrote:
> 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_...

Done.

>
> 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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