[alsa-devel] [PATCH V2 02/10] ASoC: img: Add driver for I2S input controller

[Damien Horsley]

On 28/10/15 23:43, Mark Brown wrote:
> On Wed, Oct 28, 2015 at 09:18:20PM +0000, Damien Horsley wrote:
>> On 28/10/15 01:04, Mark Brown wrote:
> 
>>>> I think it also makes sense to keep the blocks consistent with each
>>>> other. The spdif (out and in), and parallel out, all flush automatically
>>>> when stopped, and the fifo for the i2s out block is cleared when the
>>>> reset is asserted.
> 
>>> This seems like an issue that got missed in the other drivers then.  I'd
>>> expect the trigger operation to be a minimal operation which starts and
>>> stops the data transfer, not doing anything else.
> 
>> The spdif out, spdif in, and parallel out blocks auto-flush whenever
>> they are stopped. It is not possible for software to prevent this behavior.
> 
> Oh, so this isn't the drivers doing this?  In that case it's fine for
> them to do that, if it's what the hardware does it's what the hardware
> does.  It sounded like you were saying that there was similar code in
> the other drivers.
> 

For the I2S In, there is another issue with flushing on stream close. If
the stream is stopped, then reconfigured to use a larger number of
channels (without the stream being closed), then the per-channel fifos
will become inconsistent with each other. The new channels will have no
samples in their FIFOs, while the others may contain samples from the
previous stream.

Would hw_params be the correct place to flush instead?