ALSA: pcm: fix buffer_bytes max constrained by preallocated bytes issue

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  • ALSA: pcm: fix buffer_bytes max constrained by preallocated bytes issue
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Keyon Jie Jan. 16, 2020, 4:53 a.m.
With today's code, we preallocate DMA buffer for substreams at pcm_new()
stage, and the substream->buffer_bytes_max and substream->dma_max will
save as the actually preallocated buffer size and maximum size that the
dma buffer can be expanded by at hw_params() state, correspondingly.

At pcm_open() stage, the maximum constraint of HW_PARAM_BUFFER_BYTES is
set to substream->buffer_bytes_max and returned to user space as the max
interval of the HW_PARAM_BUFFER_BYTES, this will lead to issue that user
can't choose any buffer-bytes larger than the preallocated buffer size,
and the buffer reallocation will never happen actually.

Here change to use substream->dma_max as the maximum constraint of the
HW_PARAM_BUFFER_BYTES and fix the issue mentioned above.

Signed-off-by: Keyon Jie <>
 sound/core/pcm_native.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)


diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
index c375c41496f8..326e921006e7 100644
--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -2301,7 +2301,7 @@  static int snd_pcm_hw_rule_buffer_bytes_max(struct snd_pcm_hw_params *params,
 	struct snd_interval t;
 	struct snd_pcm_substream *substream = rule->private;
 	t.min = 0;
-	t.max = substream->buffer_bytes_max;
+	t.max = substream->dma_max;
 	t.openmin = 0;
 	t.openmax = 0;
 	t.integer = 1;