[ALSA] pcm core: add prealloc_max file to substream directory to show maximum DMA size

Users ask us many times about the maximum DMA size for PCM devices. This
file gives them a hint in KB.
Signed-off-by: Jaroslav Kysela <perex@suse.cz>

include/sound/pcm.h

@@ -384,6 +384,7 @@ struct snd_pcm_substream {
 	struct snd_info_entry *proc_sw_params_entry;
 	struct snd_info_entry *proc_status_entry;
 	struct snd_info_entry *proc_prealloc_entry;
+	struct snd_info_entry *proc_prealloc_max_entry;
 #endif
 	/* misc flags */
 	unsigned int hw_opened: 1;

sound/core/pcm_memory.c

@@ -101,6 +101,8 @@ int snd_pcm_lib_preallocate_free(struct snd_pcm_substream *substream)
 {
 	snd_pcm_lib_preallocate_dma_free(substream);
 #ifdef CONFIG_SND_VERBOSE_PROCFS
+	snd_info_free_entry(substream->proc_prealloc_max_entry);
+	substream->proc_prealloc_max_entry = NULL;
 	snd_info_free_entry(substream->proc_prealloc_entry);
 	substream->proc_prealloc_entry = NULL;
 #endif
@@ -141,6 +143,18 @@ static void snd_pcm_lib_preallocate_proc_read(struct snd_info_entry *entry,
 	snd_iprintf(buffer, "%lu\n", (unsigned long) substream->dma_buffer.bytes / 1024);
 }
 
+/*
+ * read callback for prealloc_max proc file
+ *
+ * prints the maximum allowed size in kB.
+ */
+static void snd_pcm_lib_preallocate_max_proc_read(struct snd_info_entry *entry,
+						  struct snd_info_buffer *buffer)
+{
+	struct snd_pcm_substream *substream = entry->private_data;
+	snd_iprintf(buffer, "%lu\n", (unsigned long) substream->dma_max / 1024);
+}
+
 /*
  * write callback for prealloc proc file
  *
@@ -203,6 +217,15 @@ static inline void preallocate_info_init(struct snd_pcm_substream *substream)
 		}
 	}
 	substream->proc_prealloc_entry = entry;
+	if ((entry = snd_info_create_card_entry(substream->pcm->card, "prealloc_max", substream->proc_root)) != NULL) {
+		entry->c.text.read = snd_pcm_lib_preallocate_max_proc_read;
+		entry->private_data = substream;
+		if (snd_info_register(entry) < 0) {
+			snd_info_free_entry(entry);
+			entry = NULL;
+		}
+	}
+	substream->proc_prealloc_max_entry = entry;
 }
 
 #else /* !CONFIG_SND_VERBOSE_PROCFS */