control: decode HDMI device name from ELD

The HDMI drivers set an uniform PCM names. Use ELD (EDID) to obtain
the HDMI device name and send this string to applications for a better
user experience.

Example (aplay -l):

  card 1: PCH [HDA Intel PCH], device 8: HDMI 2 [HDMI 2]
    Subdevices: 1/1

  vs improved:

  card 1: PCH [HDA Intel PCH], device 8: HDMI 2 [Philips 272P4]
    Subdevices: 1/1

Fixes: https://github.com/alsa-project/alsa-lib/issues/209
Signed-off-by: Jaroslav Kysela <perex@perex.cz>

src/control/Makefile.am

@@ -1,6 +1,6 @@
 EXTRA_LTLIBRARIES = libcontrol.la
 
-libcontrol_la_SOURCES = cards.c tlv.c namehint.c hcontrol.c \
+libcontrol_la_SOURCES = cards.c tlv.c eld.c namehint.c hcontrol.c \
 			control.c control_hw.c control_empty.c \
 			setup.c ctlparse.c \
 			control_plugin.c control_symbols.c

src/control/control_hw.c

@@ -287,6 +287,9 @@ static int snd_ctl_hw_pcm_info(snd_ctl_t *handle, snd_pcm_info_t * info)
 	snd_ctl_hw_t *hw = handle->private_data;
 	if (ioctl(hw->fd, SNDRV_CTL_IOCTL_PCM_INFO, info) < 0)
 		return -errno;
+	/* may be configurable (optional) */
+	if (__snd_pcm_info_eld_fixup_check(info))
+		return __snd_pcm_info_eld_fixup(info);
 	return 0;
 }
 

src/control/control_local.h

@@ -124,3 +124,12 @@ int __snd_ctl_add_elem_set(snd_ctl_t *ctl, snd_ctl_elem_info_t *info,
 int __snd_ctl_ascii_elem_id_parse(snd_ctl_elem_id_t *dst,
 				  const char *str,
 				  const char **ret_ptr);
+
+static inline int
+__snd_pcm_info_eld_fixup_check(snd_pcm_info_t *info)
+{
+	return info->stream == SND_PCM_STREAM_PLAYBACK &&
+	       strncmp((char *)info->name, "HDMI ", 5) == 0;
+}
+
+int __snd_pcm_info_eld_fixup(snd_pcm_info_t *info);

src/control/eld.c

@@ -0,0 +1,95 @@
+/**
+ * \file control/eld.c
+ * \brief ELD decoder
+ * \author Jaroslav Kysela <perex@perex>
+ * \date 2022
+ */
+/*
+ *  Control Interface - Decode ELD
+ *
+ *  Copyright (c) 2022 Jaroslav Kysela <perex@perex.cz>
+ *
+ *
+ *   This library is free software; you can redistribute it and/or modify
+ *   it under the terms of the GNU Lesser General Public License as
+ *   published by the Free Software Foundation; either version 2.1 of
+ *   the License, or (at your option) any later version.
+ *
+ *   This program is distributed in the hope that it will be useful,
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *   GNU Lesser General Public License for more details.
+ *
+ *   You should have received a copy of the GNU Lesser General Public
+ *   License along with this library; if not, write to the Free Software
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
+ *
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <string.h>
+#include "control_local.h"
+
+static void __fill_eld_ctl_id(snd_ctl_elem_id_t *id, int dev, int subdev)
+{
+	snd_ctl_elem_id_set_interface(id, SND_CTL_ELEM_IFACE_PCM);
+	snd_ctl_elem_id_set_name(id, "ELD");
+	snd_ctl_elem_id_set_device(id, dev);
+	snd_ctl_elem_id_set_index(id, subdev);
+}
+
+int __snd_pcm_info_eld_fixup(snd_pcm_info_t * info)
+{
+	snd_ctl_t *ctl;
+	snd_ctl_elem_info_t cinfo = {0};
+	snd_ctl_elem_value_t value = {0};
+	unsigned char *eld;
+	unsigned int l;
+	char *s, c;
+	int ret, valid;
+
+	ret = snd_ctl_hw_open(&ctl, NULL, info->card, 0);
+	if (ret < 0) {
+		SYSMSG("Cannot open the associated CTL\n");
+		return ret;
+	}
+
+	__fill_eld_ctl_id(&cinfo.id, info->device, info->subdevice);
+	value.id = cinfo.id;
+	ret = snd_ctl_elem_info(ctl, &cinfo);
+	if (ret >= 0 && cinfo.type == SND_CTL_ELEM_TYPE_BYTES)
+		ret = snd_ctl_elem_read(ctl, &value);
+	snd_ctl_close(ctl);
+	if (ret == -ENOENT || cinfo.type != SND_CTL_ELEM_TYPE_BYTES || cinfo.count == 0)
+		return 0;
+	if (ret < 0) {
+		SYSMSG("Cannot read ELD\n");
+		return ret;
+	}
+	/* decode connected HDMI device name */
+	eld = value.value.bytes.data;
+	if (cinfo.count < 20 || cinfo.count > 256)
+		return -EIO;
+	l = eld[4] & 0x1f;
+	if (l == 0 || l > 16 || 20 + l > cinfo.count)
+		return -EIO;
+	s = alloca(l + 1);
+	s[l] = '\0';
+	/* sanitize */
+	valid = 0;
+	while (l > 0) {
+		l--;
+		c = eld[20 + l];
+		if (c < ' ' || c >= 0x7f) {
+			s[l] = ' ';
+		} else {
+			valid += !!isalnum(c);
+			s[l] = c;
+		}
+	}
+	if (valid > 3)
+		snd_strlcpy((char *)info->name, s, sizeof(info->name));
+	return 0;
+}

src/pcm/pcm_hw.c

@@ -320,6 +320,9 @@ static int snd_pcm_hw_info(snd_pcm_t *pcm, snd_pcm_info_t * info)
 		SYSMSG("SNDRV_PCM_IOCTL_INFO failed (%i)", err);
 		return err;
 	}
+	/* may be configurable (optional) */
+	if (__snd_pcm_info_eld_fixup_check(info))
+		return __snd_pcm_info_eld_fixup(info);
 	return 0;
 }