ALSA: hda - Add Kconfig for the default buffer size

Add a Kconfig entry to specify the default buffer size.
Distros using PulseAudio can choose a larger value here.
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/pci/hda/Kconfig

@@ -14,6 +14,19 @@ menuconfig SND_HDA_INTEL
 
 if SND_HDA_INTEL
 
+config SND_HDA_PREALLOC_SIZE
+	int "Pre-allocated buffer size for HD-audio driver"
+	range 0 32768
+	default 64
+	help
+	  Speficies the default pre-allocated buffer-size in kB for
+	  HD-audio driver.  A larger buffer (e.g. 2048) is preferred
+	  for systems with PulseAudio.  The default 64 is chosen just
+	  from the compatibility reason.
+
+	  Note that the pre-allocation size can be changed dynamically
+	  via a proc file (/proc/asound/card*/pcm*/sub*/prealloc), too.
+
 config SND_HDA_HWDEP
 	bool "Build hwdep interface for HD-audio driver"
 	select SND_HWDEP

sound/pci/hda/hda_intel.c

@@ -2075,6 +2075,8 @@ static void azx_pcm_free(struct snd_pcm *pcm)
 	}
 }
 
+#define MAX_PREALLOC_SIZE	(32 * 1024 * 1024)
+
 static int
 azx_attach_pcm_stream(struct hda_bus *bus, struct hda_codec *codec,
 		      struct hda_pcm *cpcm)
@@ -2083,6 +2085,7 @@ azx_attach_pcm_stream(struct hda_bus *bus, struct hda_codec *codec,
 	struct snd_pcm *pcm;
 	struct azx_pcm *apcm;
 	int pcm_dev = cpcm->device;
+	unsigned int size;
 	int s, err;
 
 	if (pcm_dev >= HDA_MAX_PCMS) {
@@ -2118,9 +2121,12 @@ azx_attach_pcm_stream(struct hda_bus *bus, struct hda_codec *codec,
 			snd_pcm_set_ops(pcm, s, &azx_pcm_ops);
 	}
 	/* buffer pre-allocation */
+	size = CONFIG_SND_HDA_PREALLOC_SIZE * 1024;
+	if (size > MAX_PREALLOC_SIZE)
+		size = MAX_PREALLOC_SIZE;
 	snd_pcm_lib_preallocate_pages_for_all(pcm, SNDRV_DMA_TYPE_DEV_SG,
 					      snd_dma_pci_data(chip->pci),
-					      1024 * 64, 32 * 1024 * 1024);
+					      size, MAX_PREALLOC_SIZE);
 	return 0;
 }