[PATCH] ALSA: firewire-lib: remove useless operations for kernel preemption

[PATCH] ALSA: firewire-lib: remove useless operations for kernel preemption

[Takashi Sakamoto]

In all of drivers of ALSA firewire stack, the callback of .pointer and
.ack in snd_pcm_ops structure is done in acquired spin_lock of PCM
substream, therefore already under disabled kernel preemption.

Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
---
 sound/firewire/amdtp-stream.c | 14 ++------------
 1 file changed, 2 insertions(+), 12 deletions(-)

diff --git a/sound/firewire/amdtp-stream.c b/sound/firewire/amdtp-stream.c
index 945597ffacc2..1c566ddf0776 100644
--- a/sound/firewire/amdtp-stream.c
+++ b/sound/firewire/amdtp-stream.c
@@ -1751,13 +1751,8 @@ unsigned long amdtp_domain_stream_pcm_pointer(struct amdtp_domain *d,
 		// Later, the process context will sometimes schedules software
 		// IRQ context of the period_work. Then, no need to flush the
 		// queue by the same reason as described in the above
-		if (current_work() != &s->period_work) {
-			// Queued packet should be processed without any kernel
-			// preemption to keep latency against bus cycle.
-			preempt_disable();
+		if (current_work() != &s->period_work)
 			fw_iso_context_flush_completions(irq_target->context);
-			preempt_enable();
-		}
 	}
 
 	return READ_ONCE(s->pcm_buffer_pointer);
@@ -1777,13 +1772,8 @@ int amdtp_domain_stream_pcm_ack(struct amdtp_domain *d, struct amdtp_stream *s)
 
 	// Process isochronous packets for recent isochronous cycle to handle
 	// queued PCM frames.
-	if (irq_target && amdtp_stream_running(irq_target)) {
-		// Queued packet should be processed without any kernel
-		// preemption to keep latency against bus cycle.
-		preempt_disable();
+	if (irq_target && amdtp_stream_running(irq_target))
 		fw_iso_context_flush_completions(irq_target->context);
-		preempt_enable();
-	}
 
 	return 0;
 }
-- 
2.27.0

Re: [PATCH] ALSA: firewire-lib: remove useless operations for kernel preemption

[Takashi Iwai]

On Sun, 06 Jun 2021 04:56:51 +0200,
Takashi Sakamoto wrote:
> 
> In all of drivers of ALSA firewire stack, the callback of .pointer and
> .ack in snd_pcm_ops structure is done in acquired spin_lock of PCM
> substream, therefore already under disabled kernel preemption.
> 
> Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>

Thanks, applied.


Takashi