+/**
+ * amdtp_stream_add_pcm_hw_constraints - add hw constraints for PCM substream
+ * @s: the AMDTP stream, which must be initialized.
+ * @runtime: the PCM substream runtime
+ */
+int amdtp_stream_add_pcm_hw_constraints(struct amdtp_stream *s,
+ struct snd_pcm_runtime *runtime)
+{
+ int err;
+
+ /* AM824 in IEC 61883-6 can deliver 24bit data */
+ err = snd_pcm_hw_constraint_msbits(runtime, 0, 32, 24);
+ if (err < 0)
+ goto end;
+
+ /*
+ * Currently firewire-lib processes 16 packets in one software
+ * interrupt callback. This equals to 2msec but actually the
+ * interval of the interrupts has a jitter.
+ * Additionally, even if adding a constraint to fit period size to
+ * 2msec, actual calculated frames per period doesn't equal to 2msec,
+ * depending on sampling rate.
+ * Anyway, the interval to call snd_pcm_period_elapsed() cannot 2msec.
+ * Here let us use 5msec for safe period interrupt.
+ */
+ err = snd_pcm_hw_constraint_minmax(runtime,
+ SNDRV_PCM_HW_PARAM_PERIOD_TIME,
+ 5000, UINT_MAX);
+ if (err < 0)
+ goto end;
+
+ /* Non-Blocking stream has no more constraints */
+ if (!(s->flags & CIP_BLOCKING))
+ goto end;
+
+ /*
+ * One AMDTP packet can include some frames. In blocking mode, the
+ * number equals to SYT_INTERVAL. So the number is 8, 16 or 32,
+ * depending on its sampling rate. For accurate period interrupt, it's
+ * preferrable to aligh period/buffer sizes to current SYT_INTERVAL.
+ *
+ * TODO: These constraints can be improved with propper rules.
+ * Currently apply LCM of SYT_INTEVALs.
+ */
+ err = snd_pcm_hw_constraint_step(runtime, 0,
+ SNDRV_PCM_HW_PARAM_PERIOD_SIZE, 32);
+ if (err < 0)
+ goto end;
+ err = snd_pcm_hw_constraint_step(runtime, 0,
+ SNDRV_PCM_HW_PARAM_BUFFER_SIZE, 32);
+end:
+ return err;
+}
+EXPORT_SYMBOL(amdtp_stream_add_pcm_hw_constraints);
+