Re: [Sound-open-firmware] [PATCH 01/21] ASoC: SOF: Intel: Add BYT, CHT and BSW DSP HW support.

[Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>]

> I have few things to bring into discussion now, perhaps you can comment  on it.
>
> Firstly, we might want to look at the mailbox controller
> (drivers/mailbox/mailbox.c).
> It looks like the communication from AP (application processor) and
> the DSP uses shim + mailbox
> in Intel implementation, which could be abstracted by a mailbox client.
>
> The confusing part here is the naming. In the Linux kernel the shim
> layer you use is abstracted
> by the mailbox controller, while mailbox from Intel implementation is
> really a shared memory area.
>
> We have this already implemented for our mailbox (Messaging Unit) in
> drivers/mailbox/imx-mailbox.c and
> trying to integrate with SOF.
>
> So, for IPC we have the following "naming" differences:
> * imx mailbox MU - equivalent with SHIM layer from Intel SOF.
> * imx shared memory - equivalent with mailbox layer from Intel SOF.

the "shim" on the intel side is a mix of control capabilities. There are 
indeed IPC registers in there, but also clock, DMA and power control 
capabilities. I am not sure we can really remove direct access to the 
shim, it's really the host-visible set of DSP registers.

We'll look at the pointer to the i.mx mailbox, thanks for the information.

>
> Secondly, the "doorbell" naming of the interrupts. It surely looks
> like a doorbell because we notify the
> DSP that we pushed some data in a shared memory area. Anyhow, besides
> pushing data to the shared
> memory area we also send some data with the notification too.
>
> For example, in byt_send_msg we do:
>
> sof_mailbox_write(sdev, sdev->host_box.offset, msg->msg_data, msg->msg_size);
> snd_sof_dsp_write64(sdev, BYT_DSP_BAR, SHIM_IPCX, cmd | SHIM_BYT_IPCX_BUSY);
>
> Not sure how cmd is used on the DSP side. Anyhow, this is not really
> important for the next version
> of the patches. Just wanted to hear your opinion.

Humm, that one looks like an exception as well, it makes no sense. This 
is over a year old. Liam, any memories of this?