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: Takashi Sakamoto <o-takashi@sakamocchi.jp>

diff --git a/sound/firewire/amdtp-stream.c b/sound/firewire/amdtp-stream.c
index 5cdc34877fc191ecfc442861b0d50f17ac8ce741..223c880af8023c6705034de1349007c50a7eccc7 100644 (file)
--- a/sound/firewire/amdtp-stream.c
+++ b/sound/firewire/amdtp-stream.c
@@ -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)