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

[Caleb Crome]

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.