On 6/13/17 7:09 AM, Takashi Sakamoto wrote:
Pierre-Louis,
On Jun 12 2017 21:09, Pierre-Louis Bossart wrote:
If describing the detail design of your hardware, you might get more helps.
- I intentionally ignore discussion about burstness of data transmission and accuracy of hwptr.
You are probably reading too much into this. The intent is to optimize DMA operations where the hardware now knows both hw_ptr and appl_ptr. there is no use of the .ack() for copies into intermediate buffers
If this patch included enough explanation about the disadvantage of rewind operation on your driver and hardware in a point of optimization for DMA data transmission and power consumption, I would not have driven my imagination so hard for the reviewing.
Maybe you missed what we wrote in the commit message: "this can be used by low-level driver to optimize DMA operations and reduce power consumption." There will be follow-up patches that make use of this capability on Intel platforms but for now this is hardware-agnostic.
and the code for rewind on capture is largely for consistency - we've never seen anyone using rewind on capture on DSP-based platforms.
I'm not a prophet, and you too. It's not better to change interfaces with any forecast. Furthermore, once changing interfaces, it affects to all of applications. Please have enough care of it.
I don't get what you are saying. There is no interface or behavior change, disabling rewinds is strictly opt-in and controlled from the application. I was just stating that we have not seen anyone use rewinds on capture and at this point we have no need to disable non-existent usages...
# I can imagine a disadvantage of rewind operation for PCM capture # substream. When rewinding, available space on PCM buffer for data # transmission from hardware is reduced. Then, even if hardware already # done sampling, it can't transfer the PCM frames. There's a delay and # hardware needs extra buffering.
Regards
Takashi Sakamoto _______________________________________________ Alsa-devel mailing list Alsa-devel@alsa-project.org http://mailman.alsa-project.org/mailman/listinfo/alsa-devel