ALSA: PCM: Warn when buffer preallocation fails

The failures of buffer preallocations at driver initializations aren't
critical but it's still helpful to inform, so that user can know that
something doesn't work as expected.

For example, the recent page allocator change triggered regressions,
but developers didn't notice until recently because the driver didn't
complain.
Signed-off-by: NTakashi Iwai <tiwai@suse.de>

sound/core/pcm_memory.c

@@ -51,6 +51,7 @@ static const size_t snd_minimum_buffer = 16384;
 static int preallocate_pcm_pages(struct snd_pcm_substream *substream, size_t size)
 {
 	struct snd_dma_buffer *dmab = &substream->dma_buffer;
+	size_t orig_size = size;
 	int err;
 
 	do {
@@ -63,6 +64,10 @@ static int preallocate_pcm_pages(struct snd_pcm_substream *substream, size_t siz
 		size >>= 1;
 	} while (size >= snd_minimum_buffer);
 	dmab->bytes = 0; /* tell error */
+	pr_warn("ALSA pcmC%dD%d%c,%d:%s: cannot preallocate for size %zu\n",
+		substream->pcm->card->number, substream->pcm->device,
+		substream->stream ? 'c' : 'p', substream->number,
+		substream->pcm->name, orig_size);
 	return 0;
 }