[alsa-devel] fsl_ssi.c: Roberto's problem: ssi hangs after some number of samples

[Roberto Fichera]

On 11/06/2015 12:30 AM, Caleb Crome wrote:
> On Thu, Nov 5, 2015 at 3:28 PM, Roberto Fichera <kernel at tekno-soft.it> wrote:
>>
>> On 11/06/2015 12:21 AM, Caleb Crome wrote:
>>> On Thu, Nov 5, 2015 at 3:01 PM, Roberto Fichera <kernel at tekno-soft.it> wrote:
>>>> On 11/05/2015 11:49 PM, Caleb Crome wrote:
>>>>> On Thu, Nov 5, 2015 at 2:40 PM, Roberto Fichera <kernel at tekno-soft.it> wrote:
>>>>>> On 11/05/2015 11:25 PM, Caleb Crome wrote:
>>>>>>> On Thu, Nov 5, 2015 at 2:08 PM, Roberto Fichera <kernel at tekno-soft.it> wrote:
>>>>>>>> On 11/05/2015 10:34 PM, Caleb Crome wrote:
>>>>>>>>> On Thu, Nov 5, 2015 at 3:48 AM, Roberto Fichera <kernel at tekno-soft.it> wrote:
>>>>>>>>>> On 11/05/2015 12:30 PM, Fabio Estevam wrote:
>>>>>>>>>>> On Thu, Nov 5, 2015 at 8:03 AM, Roberto Fichera <kernel at tekno-soft.it> wrote:
>>>>>>>>>>>
>>>>>>>>>>>> Following your suggestion, I've increased the buffer size to 2K and set the period to fifo_length - 2 (13),
>>>>>>>>>>>> with that I'm now running substantially smooth except 3 EVTERR on RX DMA over 4 million of interrupts.
>>>>>>>>>>>>
>>>>>>>>>>>> Thanks Nicolin! I'm quite happy now!
>>>>>>>>>>> That's good progress, Roberto.
>>>>>>>>>>>
>>>>>>>>>>> It would be nice if you and Caleb could post the patches to the mailing list.
>>>>>>>>>>>
>>>>>>>>> Yes, when I get something quite solid, I'd like to submit it all to
>>>>>>>>> the list, and hope to get it into the kernel so nobody else has to go
>>>>>>>>> through this pain again.
>>>>>>>>>
>>>>>>>>>> Indeed! Now the TDM is stable, I've also found the reason of the EVTERRs, which was related to some stale
>>>>>>>>>> code I've used to enable and disable both RDMAE and TDMAE bits to try to reset the transfers.
>>>>>>>>>> Once removed that code everything is looks ok now.
>>>>>>>>>>
>>>>>>>>>> Regarding patches, well, from my side there isn't nothing special compared to the original fsl_ssi.c code.
>>>>>>>>>> I'm basically running against a very skinny fsl_ssi.c version, I've just setup a bit larger DMA buffer, from
>>>>>>>>>> 16bytes to 2K, and now reduced the DMA period to 8 because I'm mostly comfortable with that size to simplify
>>>>>>>>>> sampling exchange against DAHDI subsystem within my DMA callbacks.
>>>>>>>>>>
>>>>>>>>>> In a few words, my problem was related due to a DMA buffer too small.
>>>>>>>>>>
>>>>>>>>>> What eventually might be interesting to have is the INTRMASK and EVTERR DMA setting to trigger DMA
>>>>>>>>>> related errors, but I guess this need to be discussed elsewhere.
>>>>>>>>> I have implemented roberto's patch on the 4.2 kernel, and I get a huge
>>>>>>>>> number of EVTERR interrupts.  Something like 7200/second at 16kHz
>>>>>>>>> sample rate.  But strangely, the audio seems to be correct.
>>>>>>>> I've notice that clearing the EVTERR bit seems restarting the given SDMA.
>>>>>>>>
>>>>>>>>> My patch is slightly different in that it just enables EVTERR for all
>>>>>>>>> channels, not just for the SSI.  Might as well see if there are any
>>>>>>>>> other problems.
>>>>>>>> Oh yes! This will overload the SDMA isr.
>>>>>>> It didn't seem to.  There didn't seem to be any other DMA happening in
>>>>>>> my system, definitely none that made the EVTRR trigger.  However, I
>>>>>>> changed it back to the way you had it.  No differences, still got a
>>>>>>> TON of EVTERRs.
>>>>>> This might be related to SDMA request when another is pending.
>>>>>>
>>>>>>>> How bigger is your audio buffer?
>>>>>>>> In your case I guess you will need something like 16KHz * 16 channels *
>>>>>>>> 2 bytes (16bits) = 512K minimum.
>>>>>>>> I would try to start from 1MB or maybe more.
>>>>>>> That's 2 seconds of audio!  We definitely need less buffering than
>>>>>>> that.    We pretty much need a latency of 100ms, worst case, or 1600
>>>>>>> frames, or 51,200 bytes.
>>>>>> I haven't checked in detail how the DAI buffering is working, but likely
>>>>>> the samples are passed not in buffer size chunks but instead with less
>>>>>> granularity. Having a large buffer gives more chance to the SSI to not
>>>>>> overlap DMA requests, hence no more EVTERRs.
>>>>>>
>>>>>> I would give it a try.
>>>>>>> I did change the max buffer size to 1MB though, but I'm not sure how
>>>>>>> much is actually being used.
>>>>>> I guess it's 64K, look for IMX_SSI_DMABUF_SIZE.
>>>>>>
>>>>>>
>>>>> Exactly, I changed that to 1024*1024, but still I don't get zero
>>>>> EVTERRs, even when I set my periods long and number of periods high.
>>>> They decreased?
>>>>
>>> the big win was going to dual fifo, but they're still there at
>>> something like 17/second.
>> What about your current fifo_depth? Are you using the full length?
>>
> Do you mean in the SSI watermark, or some other FIFO depth?

Sorry! SSI watermark.

> I'm currently operating at watermark = 6 & DMA maxburst of 12 (dual fifo mode).
>
> That's the best performing so far.

Have you already played to see if increasing the watermark to 8 and
maxburst to 15 decrease the EVTERRs?
I haven't check how the SDMA script works in dual fifo mode, but I think
that in this operating mode, maxburst
might be also 16.
> -Caleb
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