ALSA: pcm: Add xrun counter for snd_pcm_substream

This patch adds an xrun counter to snd_pcm_substream as an alternative
to using logs from XRUN_DEBUG_BASIC. The counter provides a way to track
the number of xrun occurences, accessible through the /proc interface.

The counter is enabled when CONFIG_SND_PCM_XRUN_DEBUG is set.

Example output:

$ cat /proc/asound/card0/pcm9p/sub0/status

owner_pid : 1425
trigger_time: 235.248957291
tstamp : 0.000000000
delay : 1912
avail : 480
avail_max : 1920
-----
hw_ptr : 672000
appl_ptr : 673440
xrun_counter: 3 # (new row)

Signed-off-by: Norman Bintang <[e-mail]>
Reviewed-by: Chih-Yang Hsia <[e-mail]>
Tested-by: Chih-Yang Hsia <[e-mail]>
Reviewed-by: David Riley <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Takashi Iwai <[e-mail]>

include/sound/pcm.h

···
 	/* misc flags */
 	unsigned int hw_opened: 1;
 	unsigned int managed_buffer_alloc:1;
+#ifdef CONFIG_SND_PCM_XRUN_DEBUG
+	unsigned int xrun_counter; /* number of times xrun happens */
+#endif /* CONFIG_SND_PCM_XRUN_DEBUG */
 };
 
 #define SUBSTREAM_BUSY(substream) ((substream)->ref_count > 0)

sound/core/pcm.c

···
 	snd_iprintf(buffer, "-----\n");
 	snd_iprintf(buffer, "hw_ptr      : %ld\n", runtime->status->hw_ptr);
 	snd_iprintf(buffer, "appl_ptr    : %ld\n", runtime->control->appl_ptr);
+#ifdef CONFIG_SND_PCM_XRUN_DEBUG
+	snd_iprintf(buffer, "xrun_counter: %d\n", substream->xrun_counter);
+#endif
 }
 
 #ifdef CONFIG_SND_PCM_XRUN_DEBUG
···
 	substream->pid = get_pid(task_pid(current));
 	pstr->substream_opened++;
 	*rsubstream = substream;
+#ifdef CONFIG_SND_PCM_XRUN_DEBUG
+	substream->xrun_counter = 0;
+#endif /* CONFIG_SND_PCM_XRUN_DEBUG */
 	return 0;
 }
 

sound/core/pcm_lib.c

···
 		pcm_warn(substream->pcm, "XRUN: %s\n", name);
 		dump_stack_on_xrun(substream);
 	}
+#ifdef CONFIG_SND_PCM_XRUN_DEBUG
+	substream->xrun_counter++;
+#endif
 }
 
 #ifdef CONFIG_SND_PCM_XRUN_DEBUG