[alsa-devel] [v4,00/14] ASoC: Sound Open Firmware (SOF) core

[Pierre-Louis Bossart]

On 2/19/19 9:09 AM, xiang xiao wrote:
> On Tue, Feb 19, 2019 at 5:49 PM Srinivas Kandagatla
> <srinivas.kandagatla at linaro.org> wrote:
>>
>>
>> On 18/02/2019 20:03, Xiang Xiao wrote:
>>> Should we utilize official IPC frameowrk instead reinverting the wheel?
>>> 1.Load firmware by drivers/remoteproc
>>>     https://www.kernel.org/doc/Documentation/remoteproc.txt
>>> 2.Do the comunication through drivers/rpmsg
>>>     https://www.kernel.org/doc/Documentation/rpmsg.txt
>>> Many vendor(TI, Qualcomm, ST, NXP, Xilinx...) migrate to remoteproc/rpmsg, why Intel provide an other IPC mechanism?
>> It definitely makes more sense to use rpmsg for Generic IPC driver here.
>>
>> Qualcomm DSP audio drivers (non SOF) already use rpmsg. This will
>> definitely help everyone in future while immigrating to SOF.
>>
> Actually, Xiaomi also build DSP audio driver on top of rpmsg, but
> fully integrate with the ASoC topology framework, and the firmware is
> base on FreeRTOS and OpenMAX.
> SOF initiative is very good and exciting, our team members(include me)
> spend a couple weeks to study the current code base on both firmware
> and kernel side, we even port SOF to our DSP/MCU and make it run, but
> I have to point out that:
> SOF IPC is too simple and rigid, tightly couple with Intel platform
> and audio domain, which make:
>     a.It's difficult to integrate with other vendor SoC, especially if
> other vendor already adopt remote/rpmsg(this is already a trend!).
>     b.It's difficult to add other IPC services for example:
>        i.Audio DSP talk to power MCU to adjust clock and voltage
>        ii.Export ultrasonic distance measurement to IIO subsystem

The IPC scheme suggested in this patchset is only a first pass that 
works on 3 generations on Intel platforms + the QEMU  parts. There are 
no claims that the current solution is set-in-stone, and this is already 
an area where things are already changing to support notifications and 
low-power transitions.

There will clearly be evolutions to make the IPC more flexible/generic, 
but we've got to start somewhere and bear in mind that we also have to 
support memory-constrained legacy devices where such generic frameworks 
aren't needed or even implementable. Some of your proposals such as 
changing power/clocks with a firmware request aren't necessarily 
possible or recommended on all platforms - i can already hear security 
folks howling, this was already mentioned in the GitHub thread.

There are other paths such as using the mailbox framework, and at the 
end of the day the IPC is likely going to be a configurable element 
where integrators pick what's best for them. If you strongly believe 
that the RPMSG framework is the way to go, there is a public github and 
you can contribute the relevant changes with both kernel and firmware 
patches.

>
>>> Actually, remoteproc/rpmsg is much better than SOF IPC because:
>>> 1.Completely isolate the firmware load and message transfer:
>>>     The same rpmsg driver could run on any remote processor
>>> 2.Separate the application protocol from transfer layer:
>>>     One remote processor could host many rpmsg services
>>> 3.Completely follow kernel driver model(rpsmg_bus, rpmsg_device and rpmsg_driver).
>>> 4.Support by many RTOS(Bare Metal, FreeRTOS, Zephyr, NuttX, Nucleus, uC/OS...) for remote side:
>>>     https://github.com/OpenAMP/open-amp
>>>     https://github.com/NXPmicro/rpmsg-lite
>>> 5.Maintained by the standard committee:
>>>     https://www.multicore-association.org/workgroup/oamp.php
>>>     https://www.oasis-open.org/committees/tc_home.php?wg_abbrev=virtio
>>> Since the keypoint of SOF is the platform agnostic and modular, please use the standard technique here.

As stated above there is no opposition to using fancier/more generic IPC 
solutions, but they have to be considered as evolutions and follow the 
due process of contributions/reviews plus be aligned with product timelines.