[alsa-devel] Problem about developing WM8974 audio driver for MX27ipcam

[Jie Jiang]

Hi all,

I'm developing a driver for wm8974 codec with Freescale mx27ipcam board
with linux kernel 2.6.19.2. Our work is based on the mx27vis-wm8974
driver available in alsa-driver-1.0.22.

After installing all necessary driver modules, when I trying to playback
some wav file using "cat xx.wav > /dev/dsp" command, I got the following
error message:
"ALSA pcm_lib.c:1709: playback write error (DMA or IRQ trouble?)".

This seems to be caused by the full of the transmitting buffer since I
can check that "hw_ptr=0x800/buffer_size=0x4000/appl_ptr=0x4800". The
hw_ptw doesn't update anymore. It seems that there is something wrong
with the DMA operation. Actually, the DMA dest. address is the SSI1's
TX0 FIFO.  On the other hand, SSI1's SFCSR=0x440844, which indicates
that there are 8 bytes data in the TX0 FIFO, which will not generate DMA
request as the FIFO empty watermark is 4. It is very possible that the
SSI1 does not shift data from the FIFO, which causes no DMA request
generated and thus DMA freezes.

Our board connects wm8974 codec to mx27 gpio PC20~23 pins (signal name
are SSI1_XXX). On these io pins, we can check the FS and bit clock have
been generated. The PC20~PC23 gpio pins have been configure as SSI
function. My driver also configures AUDMUX host port1(HP1,wired to SSI1
internally) to peripheral port 1(PP1). But I'm not sure whether PP1 is
mapped to PC20~23. Is this configuration right? If this map is wrong,
the FS and Bit Clock generated by wm8974 can not be routed to SSI1
module, which is the potential reason for no data are shifted.

Who can shed some light on the  map between mx27 AUDMUX port and GPIO
pins?  Any more possible reasons which will freeze DMA transfer?

Regards,
Jie