[src/trunk]: src/sys/dev Allow for block sizes less than hw block size. This...

[nat <nat%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/8262699cba55
branches:  trunk
changeset: 827553:8262699cba55
user:      nat <nat%NetBSD.org@localhost>
date:      Fri Nov 03 05:07:37 2017 +0000

description:
Allow for block sizes less than hw block size.  This allows for the lowest
possible latency for all precision, sample rate and frequencies.

This is a rework of rev 1.419.

diffstat:

 sys/dev/audio.c |  24 ++++++++++++++++++++----
 1 files changed, 20 insertions(+), 4 deletions(-)

diffs (46 lines):

diff -r 1f5b369f0d77 -r 8262699cba55 sys/dev/audio.c
--- a/sys/dev/audio.c   Fri Nov 03 05:04:17 2017 +0000
+++ b/sys/dev/audio.c   Fri Nov 03 05:07:37 2017 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: audio.c,v 1.423 2017/11/03 05:04:17 nat Exp $  */
+/*     $NetBSD: audio.c,v 1.424 2017/11/03 05:07:37 nat Exp $  */
 
 /*-
  * Copyright (c) 2016 Nathanial Sloss <nathanialsloss%yahoo.com.au@localhost>
@@ -148,7 +148,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: audio.c,v 1.423 2017/11/03 05:04:17 nat Exp $");
+__KERNEL_RCSID(0, "$NetBSD: audio.c,v 1.424 2017/11/03 05:07:37 nat Exp $");
 
 #ifdef _KERNEL_OPT
 #include "audio.h"
@@ -2005,9 +2005,25 @@
                blksize = rp->s.bufsize / AUMINNOBLK;
        ROUNDSIZE(blksize);
        DPRINTF(("audio_init_ringbuffer: MI blksize=%d\n", blksize));
-       if (sc->hw_if->round_blocksize)
+
+       struct virtual_channel *hwvc = sc->sc_hwvc;
+       if (sc->hw_if->round_blocksize &&
+           (rp == &hwvc->sc_mpr || rp == &hwvc->sc_mrr)) {
                blksize = sc->hw_if->round_blocksize(sc->hw_hdl, blksize,
-                                                    mode, &rp->s.param);
+                   mode, &rp->s.param);
+       } else {
+               int hwblksize = AU_RING_SIZE;
+               if (sc->hw_if->round_blocksize) {
+                       if (audio_can_capture(sc))
+                               hwblksize = sc->sc_hwvc->sc_mpr.blksize;
+                       else
+                               hwblksize = sc->sc_hwvc->sc_mrr.blksize;
+               }
+
+               if (blksize > hwblksize)
+                       blksize = hwblksize;
+       }
+
        if (blksize <= 0)
                panic("audio_init_ringbuffer: blksize=%d", blksize);
        nblks = rp->s.bufsize / blksize;