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

Mathias Nyman
2015-10-29T14:04:38Z

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@asmedia.com.tw>
>>> Signed-off-by: Lu Baolu <baolu.lu@linux.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