From d3d120fa281134735fc4b113d0bcd7e4e1929ea9 Mon Sep 17 00:00:00 2001
From: Robin Gareus <robin@gareus.org>
Date: Tue, 28 Apr 2020 03:28:34 +0200
Subject: [PATCH] Prepare to allow using ALSA backend with nperiods > 3

This will still need an update for Alsa_pcmi::set_hwpar() capture
channel (which is fixed at 2, unless FRAG_NEAR is used).
---
 .../ardouralsautil/deviceinfo.h               |  1 +
 libs/ardouralsautil/deviceparams.cc           | 19 +++++--------
 libs/backends/alsa/alsa_audiobackend.cc       | 27 ++++++++++++++++---
 3 files changed, 30 insertions(+), 17 deletions(-)

diff --git a/libs/ardouralsautil/ardouralsautil/deviceinfo.h b/libs/ardouralsautil/ardouralsautil/deviceinfo.h
index d0a1b7ec18..e217a0d575 100644
--- a/libs/ardouralsautil/ardouralsautil/deviceinfo.h
+++ b/libs/ardouralsautil/ardouralsautil/deviceinfo.h
@@ -24,6 +24,7 @@ namespace ARDOUR {
 	struct ALSADeviceInfo {
 		unsigned int max_channels;
 		unsigned int min_rate, max_rate;
+		unsigned int min_nper, min_nper;
 		unsigned long min_size, max_size;
 		bool valid;
 	};
diff --git a/libs/ardouralsautil/deviceparams.cc b/libs/ardouralsautil/deviceparams.cc
index 2e9bca95f6..613eac76e0 100644
--- a/libs/ardouralsautil/deviceparams.cc
+++ b/libs/ardouralsautil/deviceparams.cc
@@ -34,7 +34,6 @@ ARDOUR::get_alsa_device_parameters (const char* device_name, const bool play, AL
 
 	unsigned long min_psiz, max_psiz;
 	unsigned long min_bufz, max_bufz;
-	unsigned int min_nper, max_nper;
 
 	err = snd_pcm_open (&pcm, device_name,
 			play ? SND_PCM_STREAM_PLAYBACK : SND_PCM_STREAM_CAPTURE,
@@ -91,12 +90,12 @@ ARDOUR::get_alsa_device_parameters (const char* device_name, const bool play, AL
 		goto error_out;
 	}
 
-	err = snd_pcm_hw_params_get_periods_min (hw_params, &min_nper, 0);
+	err = snd_pcm_hw_params_get_periods_min (hw_params, &nfo->min_nper, 0);
 	if (err < 0) {
 		errmsg = "Cannot get minimum period count";
 		goto error_out;
 	}
-	err = snd_pcm_hw_params_get_periods_max (hw_params, &max_nper, 0);
+	err = snd_pcm_hw_params_get_periods_max (hw_params, &nfo->max_nper, 0);
 	if (err < 0) {
 		errmsg = "Cannot get maximum period count";
 		goto error_out;
@@ -117,19 +116,13 @@ ARDOUR::get_alsa_device_parameters (const char* device_name, const bool play, AL
 		fprintf (stdout, "  max_psiz : %lu\n", nfo->max_size);
 		fprintf (stdout, "  min_bufz : %lu\n", min_bufz);
 		fprintf (stdout, "  max_bufz : %lu\n", max_bufz);
-		fprintf (stdout, "  min_nper : %d\n", min_nper);
-		fprintf (stdout, "  max_nper : %d\n", max_nper);
+		fprintf (stdout, "  min_nper : %d\n", nfo->min_nper);
+		fprintf (stdout, "  max_nper : %d\n", nfo->max_nper);
 		fprintf (stdout, "  possible : %lu .. %lu\n", nfo->min_size, nfo->max_size);
 	}
 
-	/* AlsaAudioBackend supports n-periods 2, 3 */
-	if (min_nper > 2 || max_nper < 3) {
-		errmsg = "Unsupported period count";
-		return 1;
-	}
-
-	nfo->min_size = std::max (min_psiz, min_bufz / 3);
-	nfo->max_size = std::min (max_psiz, max_bufz / 2);
+	nfo->min_size = std::max (min_psiz, min_bufz / nfo->max_nper);
+	nfo->max_size = std::min (max_psiz, max_bufz / nfo->min_nper);
 	nfo->valid = true;
 	return 0;
 
diff --git a/libs/backends/alsa/alsa_audiobackend.cc b/libs/backends/alsa/alsa_audiobackend.cc
index 7dec3eb738..6c931b08cb 100644
--- a/libs/backends/alsa/alsa_audiobackend.cc
+++ b/libs/backends/alsa/alsa_audiobackend.cc
@@ -270,8 +270,27 @@ std::vector<uint32_t>
 AlsaAudioBackend::available_period_sizes (const std::string& driver) const
 {
 	std::vector<uint32_t> ps;
-	ps.push_back (2);
-	ps.push_back (3);
+
+	ALSADeviceInfo *nfo = NULL;
+	if (device == get_standard_device_name(DeviceNone)) {
+		return ps;
+	}
+	if (device == _output_audio_device && _output_audio_device_info.valid) {
+		nfo = &_output_audio_device_info;
+	} else {
+		ps.push_back (2);
+		return ps;
+	}
+
+	if (nfo->min_nper == 2) {
+		ps.push_back (2);
+		if (nfo->max_nper >= 3) {
+			ps.push_back (3);
+		}
+	} else {
+		ps.push_back (nfo->min_nper);
+	}
+
 	return ps;
 }
 
@@ -370,7 +389,7 @@ AlsaAudioBackend::set_sample_rate (float sr)
 int
 AlsaAudioBackend::set_peridod_size (uint32_t n)
 {
-	if (n == 0 || n > 3) {
+	if (n == 0) {
 		return -1;
 	}
 	if (_run) {
@@ -830,7 +849,7 @@ AlsaAudioBackend::_start (bool for_latency_measurement)
 			(duplex & 1) ? alsa_device.c_str() : NULL,
 			/* ctrl name */ 0,
 			_samplerate, _samples_per_period,
-			_periods_per_cycle, /* _periods_per_cycle */ 2,
+			_periods_per_cycle, /* capture p/c */ 2,
 			/* debug */ 0);
 
 	AudioBackend::ErrorCode error_code = NoError;