brcm2708: update to latest patches from RPi foundation

[openwrt/openwrt.git] / target / linux / brcm2708 / patches-4.19 / 950-0408-staging-bcm2835-audio-interpolate-audio-delay.patch

diff --git a/target/linux/brcm2708/patches-4.19/950-0408-staging-bcm2835-audio-interpolate-audio-delay.patch b/target/linux/brcm2708/patches-4.19/950-0408-staging-bcm2835-audio-interpolate-audio-delay.patch
new file mode 100644 (file)
index 0000000..cf5f11c
--- /dev/null
+++ b/target/linux/brcm2708/patches-4.19/950-0408-staging-bcm2835-audio-interpolate-audio-delay.patch
@@ -0,0 +1,82 @@
+From 2ba82d9516203ce41f33e98adb667bedee3622bc Mon Sep 17 00:00:00 2001
+From: Mike Brady <mikebrady@eircom.net>
+Date: Mon, 22 Oct 2018 20:17:08 +0100
+Subject: [PATCH] staging: bcm2835-audio: interpolate audio delay
+
+commit a105a3a72824e0ac685a0711a67e4dbe29de62d0 upstream.
+
+When the BCM2835 audio output is used, userspace sees a jitter up to 10ms
+in the audio position, aka "delay" -- the number of frames that must
+be output before a new frame would be played.
+Make this a bit nicer for userspace by interpolating the position
+using the CPU clock.
+The overhead is small -- an extra ktime_get() every time a GPU message
+is sent -- and another call and a few calculations whenever the delay
+is sought from userland.
+At 48,000 frames per second, i.e. approximately 20 microseconds per
+frame, it would take a clock inaccuracy of
+20 microseconds in 10 milliseconds -- 2,000 parts per million --
+to result in an inaccurate estimate, whereas
+crystal- or resonator-based clocks typically have an
+inaccuracy of 10s to 100s of parts per million.
+
+Signed-off-by: Mike Brady <mikebrady@eircom.net>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+---
+ .../vc04_services/bcm2835-audio/bcm2835-pcm.c | 20 +++++++++++++++++++
+ .../vc04_services/bcm2835-audio/bcm2835.h     |  1 +
+ 2 files changed, 21 insertions(+)
+
+--- a/drivers/staging/vc04_services/bcm2835-audio/bcm2835-pcm.c
++++ b/drivers/staging/vc04_services/bcm2835-audio/bcm2835-pcm.c
+@@ -74,6 +74,7 @@ void bcm2835_playback_fifo(struct bcm283
+       atomic_set(&alsa_stream->pos, pos);
+ 
+       alsa_stream->period_offset += bytes;
++      alsa_stream->interpolate_start = ktime_get();
+       if (alsa_stream->period_offset >= alsa_stream->period_size) {
+               alsa_stream->period_offset %= alsa_stream->period_size;
+               snd_pcm_period_elapsed(substream);
+@@ -237,6 +238,7 @@ static int snd_bcm2835_pcm_prepare(struc
+       atomic_set(&alsa_stream->pos, 0);
+       alsa_stream->period_offset = 0;
+       alsa_stream->draining = false;
++      alsa_stream->interpolate_start = ktime_get();
+ 
+       return 0;
+ }
+@@ -286,6 +288,24 @@ snd_bcm2835_pcm_pointer(struct snd_pcm_s
+ {
+       struct snd_pcm_runtime *runtime = substream->runtime;
+       struct bcm2835_alsa_stream *alsa_stream = runtime->private_data;
++      ktime_t now = ktime_get();
++
++      /* Give userspace better delay reporting by interpolating between GPU
++       * notifications, assuming audio speed is close enough to the clock
++       * used for ktime
++       */
++
++      if ((ktime_to_ns(alsa_stream->interpolate_start)) &&
++          (ktime_compare(alsa_stream->interpolate_start, now) < 0)) {
++              u64 interval =
++                      (ktime_to_ns(ktime_sub(now,
++                              alsa_stream->interpolate_start)));
++              u64 frames_output_in_interval =
++                      div_u64((interval * runtime->rate), 1000000000);
++              snd_pcm_sframes_t frames_output_in_interval_sized =
++                      -frames_output_in_interval;
++              runtime->delay = frames_output_in_interval_sized;
++      }
+ 
+       return snd_pcm_indirect_playback_pointer(substream,
+               &alsa_stream->pcm_indirect,
+--- a/drivers/staging/vc04_services/bcm2835-audio/bcm2835.h
++++ b/drivers/staging/vc04_services/bcm2835-audio/bcm2835.h
+@@ -78,6 +78,7 @@ struct bcm2835_alsa_stream {
+       unsigned int period_offset;
+       unsigned int buffer_size;
+       unsigned int period_size;
++      ktime_t interpolate_start;
+ 
+       struct bcm2835_audio_instance *instance;
+       int idx;