Unable to open hostless PCM device after introduction of commit - ASoC: Stop dummy from overriding hwparams

[Patrick Lai]

Hi Amadeusz,

On the product I am working on, a hostless PCM device is defined for 
purpose of activating CODEC driver to setup the path inside CODEC. So, 
CPU DAI and PCM Platform are defined to use dummy dai & DMA supplied by 
sound/soc/soc-utils.c.

After upgrading to newer kernel, hostless PCM device failed to open. 
After doing a bit of digging, the root cause is that dummy_dma_hardware 
is not set in dummy_dma_open() due to new conditional check logic 
introduced in this commit - 6c504663ba2ee2abeaf5622e27082819326c1bd4.

In order to fix problem I am encountering properly without regressing 
your scenario, I would like to get a better understanding of problem you 
were addressing. My understanding, from looking through other drivers 
under sound/soc, is that pcm hardware info is usually set by PCM 
platform/DMA drivers. For your scenario, do you have other component e.g 
CPU/CODEC DAI, set PCM hardware definition? I am not sure conditional 
check logic from 6c504663ba2ee2abeaf5622e27082819326c1bd4 guarantees 
that other component would be setting pcm hardware info. Appreciate if 
you can provide more insight to your scenario?

Thanks
Patrick