Subject: [PATCH v2] ARM: pl330: Fix a race condition

From: [email-masked] (Javi Merino)
Date: Tue, 29 Nov 2011 09:53:30 +0000

On 29/11/11 03:41, Boojin Kim wrote:
> Javi Merino wrote:
> 
> 
>>>
>>>>> On Samsung's Exynos4 platform, while testing audio playback with
>> i2s
>>>>> interface, the above change causes the playback to freeze. The
>>>>> _thrd_active(thrd) call always returns '1' and hence _start(thrd)
>> is
>>>>> not getting called.
>>>>
>>>> If _thrd_active(thrd) returns '1', that means there is an active
>>>> transfer still running or, if it has finished, you haven't called
>>>> pl330_update() to acknowledge that.  pl330_update() calls _start()
>> as
>>>> soon as it can.
>>>>
>>>> drivers/dma/pl330.c registers the irq handler in pl330_probe(), so
>>>> when
>>>> the transaction finishes, pl330_update() should clear it and call
>>>> _start().  If there is any outstanding transaction, it should start
>>>> straight away. If there isn't, it would mark the channel as free,
>> so
>>>> _thrd_active() should return '0'.  If _thrd_active() is still '1',
>> then
>>>> something has gone wrong in the way.
>>>>
>>>> Does this shed some light?
>>>>
>>>
>>> Your patch makes the memcpy operation on dmatest.c and net DMA be
>> frozen too
>>> as well as Samsung audio playback.
>>
>> Is the IRQ correctly registered in drivers/dma/pl330.c:pl330_probe()?
>> Do you get interrupts when the transfer finish?
> Sure. IRQ works well.

Ok, so can you check if pl330_update() is correctly marking the request
as free?  Do you know if there is another request in the queue when that
happens?

Thomas, you said in a previous email that _thrd_active() always returned
'1'.  Was that after a request in req[0] finished?
  - If so, can you check that MARK_FREE was actually called for that
    request in pl330_update()?
  - If it was after a request in req[1] finished and there was a
    request already waiting in req[0], can you debug why _start()
    didn't activate it.

Cheers,
Javi