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Subject: Re: [PATCH v6 6/9] ALSA: virtio: PCM substream operators

On 28.02.2021 12:32, Takashi Iwai wrote:
On Sat, 27 Feb 2021 09:59:53 +0100,
Anton Yakovlev wrote:


+static snd_pcm_uframes_t
+virtsnd_pcm_pointer(struct snd_pcm_substream *substream)
+     struct virtio_pcm_substream *vss = snd_pcm_substream_chip(substream);
+     snd_pcm_uframes_t hw_ptr = SNDRV_PCM_POS_XRUN;
+     unsigned long flags;
+     spin_lock_irqsave(&vss->lock, flags);
+     if (!vss->xfer_xrun)
+             hw_ptr = bytes_to_frames(substream->runtime, vss->hw_ptr);
+     spin_unlock_irqrestore(&vss->lock, flags);

Oh, and if we drop nonatomc PCM, both trigger and pointer callbacks
are guaranteed to be called inside the spinlock, hence you can remove
*_irqsave() but just us spin_lock() in those two callbacks.

As I understand, spin_lock_irqsave() disables only local interrupts. But
what about other CPU cores?



Anton Yakovlev
Senior Software Engineer

OpenSynergy GmbH
Rotherstr. 20, 10245 Berlin

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