Commit 6b617317 authored by Takashi Sakamoto's avatar Takashi Sakamoto
Browse files

ALSA: firewire: remove PCM buffer size constraint from isoc context header 

In the IEC 61883-1/6 packet streaming engine, the isochronous context
header stores CIP headers. Previously, the header storage was limited to
PAGE_SIZE, which constrained the maximum PCM buffer size.

There is a function with configurable header size. Now the limitation is
removed.

Link: https://lore.kernel.org/r/20260117142823.440811-10-o-takashi@sakamocchi.jp


Signed-off-by: default avatarTakashi Sakamoto <o-takashi@sakamocchi.jp>
parent e5f1291b

sound/firewire/amdtp-stream.c

+9 −22
Original line number Diff line number Diff line
@@ -191,8 +191,6 @@ int amdtp_stream_add_pcm_hw_constraints(struct amdtp_stream *s, 
					struct snd_pcm_runtime *runtime)

{

	struct snd_pcm_hardware *hw = &runtime->hw;

	unsigned int ctx_header_size;

	unsigned int maximum_usec_per_period;

	int err;



	hw->info = SNDRV_PCM_INFO_BLOCK_TRANSFER |
@@ -212,21 +210,6 @@ int amdtp_stream_add_pcm_hw_constraints(struct amdtp_stream *s, 
	hw->period_bytes_max = hw->period_bytes_min * 2048;

	hw->buffer_bytes_max = hw->period_bytes_max * hw->periods_min;



	// Linux driver for 1394 OHCI controller voluntarily flushes isoc

	// context when total size of accumulated context header reaches

	// PAGE_SIZE. This kicks work for the isoc context and brings

	// callback in the middle of scheduled interrupts.

	// Although AMDTP streams in the same domain use the same events per

	// IRQ, use the largest size of context header between IT/IR contexts.

	// Here, use the value of context header in IR context is for both

	// contexts.

	if (!(s->flags & CIP_NO_HEADER))

		ctx_header_size = IR_CTX_HEADER_SIZE_CIP;

	else

		ctx_header_size = IR_CTX_HEADER_SIZE_NO_CIP;

	maximum_usec_per_period = USEC_PER_SEC * PAGE_SIZE /

				  CYCLES_PER_SECOND / ctx_header_size;



	// In IEC 61883-6, one isoc packet can transfer events up to the value

	// of syt interval. This comes from the interval of isoc cycle. As 1394

	// OHCI controller can generate hardware IRQ per isoc packet, the
@@ -239,9 +222,10 @@ int amdtp_stream_add_pcm_hw_constraints(struct amdtp_stream *s, 
	// Due to the above protocol design, the minimum PCM frames per

	// interrupt should be double of the value of syt interval, thus it is

	// 250 usec.

	// There is no reason, but up to 250 msec to avoid consuming resources so much.

	err = snd_pcm_hw_constraint_minmax(runtime,

					   SNDRV_PCM_HW_PARAM_PERIOD_TIME,

					   250, maximum_usec_per_period);

					   250, USEC_PER_SEC / 4);

	if (err < 0)

		goto end;
@@ -261,6 +245,7 @@ int amdtp_stream_add_pcm_hw_constraints(struct amdtp_stream *s, 
				  SNDRV_PCM_HW_PARAM_RATE, -1);

	if (err < 0)

		goto end;



	err = snd_pcm_hw_rule_add(runtime, 0, SNDRV_PCM_HW_PARAM_BUFFER_SIZE,

				  apply_constraint_to_size, NULL,

				  SNDRV_PCM_HW_PARAM_BUFFER_SIZE,
@@ -1715,7 +1700,9 @@ static int amdtp_stream_start(struct amdtp_stream *s, int channel, int speed, 
	} else {

		dir = DMA_TO_DEVICE;

		type = FW_ISO_CONTEXT_TRANSMIT;

		ctx_header_size = 0;	// No effect for IT context.

		// Although no effect for IT context, this value is required to compute the size

		// of header storage correctly.

		ctx_header_size = sizeof(__be32);

	}

	max_ctx_payload_size = amdtp_stream_get_max_ctx_payload_size(s);
@@ -1724,9 +1711,9 @@ static int amdtp_stream_start(struct amdtp_stream *s, int channel, int speed, 
		return err;

	s->queue_size = queue_size;



	s->context = fw_iso_context_create(fw_parent_device(s->unit)->card,

					  type, channel, speed, ctx_header_size,

					  amdtp_stream_first_callback, s);

	s->context = fw_iso_context_create_with_header_storage_size(

			fw_parent_device(s->unit)->card, type, channel, speed, ctx_header_size,

			ctx_header_size * queue_size, amdtp_stream_first_callback, s);

	if (IS_ERR(s->context)) {

		err = PTR_ERR(s->context);

		if (err == -EBUSY)