[alsa-devel] [PATCH v3 04/14] ASoC: SOF: Add support for IPC IO between DSP and Host

[Mark Brown]

On Tue, Jan 22, 2019 at 03:05:23PM -0600, Pierre-Louis Bossart wrote:
> On 1/22/19 1:04 PM, Mark Brown wrote:
> > On Thu, Jan 10, 2019 at 02:11:32PM -0600, Pierre-Louis Bossart wrote:

> > > Messages can be as big as the mailbox, which is hardware dependent. It could
> > > be from a few bytes to a larger e.g. 4k page or more, and indeed we need to
> > > keep the lock.

> > Is this copying into an actual mailbox or into some data structure in
> > memory?  It looked like it's copying into a buffer for sending rather
> > than the mailbox.

> I realize between your feedback and Daniel's that we have a terminology
> issue. On the Intel side we don't have a dedicated hardware mailbox unit,
> it's only doorbell registers and shared memory windows.

Ah, that's what I thought was going on.  What I was expecting was a
sequence of operations along the lines of:

  1. Allocate a buffer for the message.
  2. Fill in the message.
  3. Mark the message as readable by the DSP.

so you only need locking for steps 1 and 3 (and a similar path on
return).
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