Hi Takashi-san
# Oops !? # You and Iwai-san are both same name :)
OK, thank you for your explanation. My current driver updates snd_pcm_ops::pointer only when DMA transfer was finished, but I guess it needs to adjust to update it during transfer, too. I think I can use dmaengine_tx_status() for this purpose. I don't know how to know about delay, but I will try update pointer as 1st step.
If your driver calls 'snd_pcm_period_elapsed()' in any hw/sw IRQ context, it's correct. But 'struct snd_pcm_ops.pointer' callback is not only executed by the function, but also in the other contexts such as ioctl(2) with HWSYNC.
In design of ALSA PCM core, the callback is expected to return the number of PCM frames currently transferred via physical audio serial bus, inner PCM period boundary. As long as I know, recent hardwares have any register for this purpose and your driver could calculate the number.
The 'accuracy' represents how accurate the returned number is, against actual transferring via audio serial bus.
Thank you for your detail explanation. I will adjust my driver
Best regards --- Kuninori Morimoto