[alsa-devel] fsl_ssi.c: Getting channel slips with fsl_ssi.c in TDM (network) mode.

[arnaud.mouiche at invoxia.com]

Le 20/10/2015 19:43, Caleb Crome a écrit :
> On Tue, Oct 20, 2015 at 12:36 AM, arnaud.mouiche at invoxia.com
> <arnaud.mouiche at invoxia.com> wrote:
>> Hello Caleb,
>>
>> I go through all [few] patchs we apply to the 4.0 linux tree (didn't jump to
>> 4.2 yet).
>> There is one concerning the DMA firmware you can find in the freescale tree,
>> available at git://git.freescale.com/imx/linux-2.6-imx.git
>>
>> commit 619bfca89908b90cd6606ed894c180df0c481508
>> Author: Shawn Guo <shawn.guo at freescale.com>
>> Date:   Tue Jul 16 22:53:18 2013 +0800
>>
>>      ENGR00269945: firwmare: imx: add imx6q sdma script
>>
>>      Add imx6q sdma script which will be used by all i.MX6 series.
>>
>>      Signed-off-by: Shawn Guo <shawn.guo at freescale.com>
>>
>>   firmware/Makefile                     |   1 +
>>   firmware/imx/sdma/sdma-imx6q.bin.ihex | 116
>> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>>   2 files changed, 117 insertions(+)
>>
>>
>> I don't know how 4.3rcN catch some of the freescale patch. but you may check
>> if you need to apply this one.
>> I know there are some other SDMA firmware available all around in this
>> freescale tree. I didn't find proper release note or documentation. May be
>> you can test them also.
>>
>> Arnaud
> Hi Arnaud,
>    My root filesystem already had that firmware in it (the kernel
> didn't have the kernel patch, but when I applied that patch, the
> generated sdma script was identical.
>
> So, unfortunately, that's not the problem with the channel slipping.
> Any other thoughts on why the channel would slip?  Or pointers on how
> to diagnose?  I have an oscilloscope & know how to use it :-)  Also, I
> can flip a GPIO to watch for timing of interrupts, etc (although I
> haven't done that yet).
>
>
> Thanks,
>    -Caleb

Hello Caleb,

In your situation, I would:
- check if TUE0/1 flag never rise (Transmitter Underrun) by activating 
the TUE0/1IE bit to generate related interrupts. It looks like already 
enabled in 4.0 by collecting statistics with fsl_ssi_dbg_isr(). Despite 
there is no printk message on underrun, stats can be read from 
/sys/kernel/debug/xxxx.ssi/stats.

- I suspect the dma is not fast enough to fill the FIFO. may be you 
should dig to check how SDMA priority are configured amongs the 
differents DMA channels.
Not something I already look at before. A quick look suggest that 
DMA_PRIO_HIGH is _NOT_ configured by the fsl_ssi.c driver (wheras the 
imx-ssi.c did)

Regards,
Arnaud