Re: [PATCH v4 6/6] ALSA: led control - add sysfs kcontrol LED marking layer

From: Takashi Iwai <tiwai@suse.de>
To: Hans de Goede <hdegoede@redhat.com>
Cc: ALSA development <alsa-devel@alsa-project.org>
Subject: Re: [PATCH v4 6/6] ALSA: led control - add sysfs kcontrol LED marking layer
Date: Fri, 19 Mar 2021 18:22:48 +0100	[thread overview]
Message-ID: <s5h5z1nf47r.wl-tiwai@suse.de> (raw)
In-Reply-To: <a3ddb881-6580-cd25-ef3c-734e686e6942@redhat.com>

On Fri, 19 Mar 2021 17:34:39 +0100,
Hans de Goede wrote:
> 
> Hi,
> 
> On 3/17/21 6:29 PM, Jaroslav Kysela wrote:
> > We need to manage the kcontrol entries association for the LED trigger
> > from the user space. This patch adds a layer to the sysfs tree like:
> > 
> > /sys/devices/virtual/sound/ctl-led/mic
> >    + card0
> >    |  + attach
> >    |  + detach
> >    |  ...
> >    + card1
> >       + attach
> >       ...
> > 
> > Operations:
> > 
> >   attach and detach
> >     - amixer style ID is accepted and easy strings for numid and
> >       simple names
> >   reset
> >     - reset all associated kcontrol entries
> >   list
> >     - list associated kcontrol entries (numid values only)
> > 
> > Additional symlinks:
> > 
> > /sys/devices/virtual/sound/ctl-led/mic/card0/card ->
> >   /sys/class/sound/card0
> > 
> > /sys/class/sound/card0/controlC0/led-mic ->
> >   /sys/devices/virtual/sound/ctl-led/mic/card0
> > 
> > Signed-off-by: Jaroslav Kysela <perex@perex.cz>
> 
> Thank you so much for this patch.
> 
> I've given this new version a try, dropping my sound/soc/codecs/rt56??.c patches to set the access-flags directly.
> 
> And with these 3 lines in /etc/rc.d/rc.local I get nicely working control of the mute
> LED build into the (detachable) USB-keyboard's mute hot-key:
> 
> modprobe snd_ctl_led
> echo -n name="Speaker Channel Switch" > /sys/class/sound/card1/controlC1/led-speaker/attach
> echo -n name="HP Channel Switch" > /sys/class/sound/card1/controlC1/led-speaker/attach
> 
> This needs to be replaced by some UCM profile code doing the equivalent of course,
> but for a proof-of-concept test of the kernel API this introduces the above will do.

IMO, that's the question: how we'll enable this in future.  If the
binding of the control/mute mapping is provided via UCM, it's supposed
to be changeable by each user.  Then the current sysfs permission
doesn't fit.  OTOH, if it's 0666, it's accessible to all users even
remotely, which is worse than the access with the normal sound device
file.  Or if it's supposed to be changed via udev stuff or systemd?
Or is it just for debugging?

Through a quick glance over the series, I'm fine to take those
patches, but the only concern is the sysfs entries.  Basically, once
when we use sysfs entries, it's set in stone.  So we should be very
clear about our strategy how to deploy the control/mute mapping
regarding using those sysfs entries.

OTOH, if the interface is thought for debugging or development
purpose, it could be done in debugfs, which we can keep playing in
further development, too.

And, BTW, the mute LED mode setup doesn't have to be sysfs entries;
we'd need primarily only the flags for inverted LED behavior, and
those are only two, so it could be simply module options.  Then it's
even easier for users to set up than tweaking sysfs entries.

thanks,

Takashi

> 
> Only complaint which I have is the need to add "-n" to the echo commands,
> it would be nice if set_led_id() would check if the copy which it stores in buf2
> ends with "\n" and if it does if it would then strip that from the copy in buf2.
> 
> Regards,
> 
> Hans
> 
> 
> p.s.
> 
> Note this does need my recently listed alsa=lib patches so that these "Channel Switch" controls
> get grouped with the "Speaker Playback Volume" / "HP Playback Volume" controls, so that the
> volume-hw control code will actually toggle them:
> 
> https://lore.kernel.org/alsa-devel/20210307133005.30801-1-hdegoede@redhat.com/T/#u
> 
> Talking about that series, what is the status of that ? From my POV it
> is ready for merging...
> 
> 
> 
> > ---
> >  sound/core/control_led.c | 366 ++++++++++++++++++++++++++++++++++++++-
> >  1 file changed, 362 insertions(+), 4 deletions(-)
> > 
> > diff --git a/sound/core/control_led.c b/sound/core/control_led.c
> > index dfa51d8461e1..d4fb8b873f34 100644
> > --- a/sound/core/control_led.c
> > +++ b/sound/core/control_led.c
> > @@ -24,6 +24,12 @@ enum snd_ctl_led_mode {
> >  	 MODE_ON,
> >  };
> >  
> > +struct snd_ctl_led_card {
> > +	struct device dev;
> > +	int number;
> > +	struct snd_ctl_led *led;
> > +};
> > +
> >  struct snd_ctl_led {
> >  	struct device dev;
> >  	struct list_head controls;
> > @@ -31,6 +37,7 @@ struct snd_ctl_led {
> >  	unsigned int group;
> >  	enum led_audio trigger_type;
> >  	enum snd_ctl_led_mode mode;
> > +	struct snd_ctl_led_card *cards[SNDRV_CARDS];
> >  };
> >  
> >  struct snd_ctl_led_ctl {
> > @@ -58,6 +65,9 @@ static struct snd_ctl_led snd_ctl_leds[MAX_LED] = {
> >  	},
> >  };
> >  
> > +static void snd_ctl_led_sysfs_add(struct snd_card *card);
> > +static void snd_ctl_led_sysfs_remove(struct snd_card *card);
> > +
> >  #define UPDATE_ROUTE(route, cb) \
> >  	do { \
> >  		int route2 = (cb); \
> > @@ -222,6 +232,46 @@ static void snd_ctl_led_notify(struct snd_card *card, unsigned int mask,
> >  	}
> >  }
> >  
> > +static int snd_ctl_led_set_id(int card_number, struct snd_ctl_elem_id *id,
> > +			      unsigned int group, bool set)
> > +{
> > +	struct snd_card *card;
> > +	struct snd_kcontrol *kctl;
> > +	struct snd_kcontrol_volatile *vd;
> > +	unsigned int ioff, access, new_access;
> > +	int err = 0;
> > +
> > +	card = snd_card_ref(card_number);
> > +	if (card) {
> > +		down_write(&card->controls_rwsem);
> > +		kctl = snd_ctl_find_id(card, id);
> > +		if (kctl) {
> > +			ioff = snd_ctl_get_ioff(kctl, id);
> > +			vd = &kctl->vd[ioff];
> > +			access = vd->access & SNDRV_CTL_ELEM_ACCESS_LED_MASK;
> > +			if (access != 0 && access != group_to_access(group)) {
> > +				err = -EXDEV;
> > +				goto unlock;
> > +			}
> > +			new_access = vd->access & ~SNDRV_CTL_ELEM_ACCESS_LED_MASK;
> > +			if (set)
> > +				new_access |= group_to_access(group);
> > +			if (new_access != vd->access) {
> > +				vd->access = new_access;
> > +				snd_ctl_led_notify(card, SNDRV_CTL_EVENT_MASK_INFO, kctl, ioff);
> > +			}
> > +		} else {
> > +			err = -ENOENT;
> > +		}
> > +unlock:
> > +		up_write(&card->controls_rwsem);
> > +		snd_card_unref(card);
> > +	} else {
> > +		err = -ENXIO;
> > +	}
> > +	return err;
> > +}
> > +
> >  static void snd_ctl_led_refresh(void)
> >  {
> >  	unsigned int group;
> > @@ -230,6 +280,12 @@ static void snd_ctl_led_refresh(void)
> >  		snd_ctl_led_set_state(NULL, group_to_access(group), NULL, 0);
> >  }
> >  
> > +static void snd_ctl_led_ctl_destroy(struct snd_ctl_led_ctl *lctl)
> > +{
> > +	list_del(&lctl->list);
> > +	kfree(lctl);
> > +}
> > +
> >  static void snd_ctl_led_clean(struct snd_card *card)
> >  {
> >  	unsigned int group;
> > @@ -241,13 +297,47 @@ static void snd_ctl_led_clean(struct snd_card *card)
> >  repeat:
> >  		list_for_each_entry(lctl, &led->controls, list)
> >  			if (!card || lctl->card == card) {
> > -				list_del(&lctl->list);
> > -				kfree(lctl);
> > +				snd_ctl_led_ctl_destroy(lctl);
> >  				goto repeat;
> >  			}
> >  	}
> >  }
> >  
> > +static int snd_ctl_led_reset(int card_number, unsigned int group)
> > +{
> > +	struct snd_card *card;
> > +	struct snd_ctl_led *led;
> > +	struct snd_ctl_led_ctl *lctl;
> > +	struct snd_kcontrol_volatile *vd;
> > +	bool change = false;
> > +
> > +	card = snd_card_ref(card_number);
> > +	if (!card)
> > +		return -ENXIO;
> > +
> > +	mutex_lock(&snd_ctl_led_mutex);
> > +	if (!snd_ctl_led_card_valid[card_number]) {
> > +		mutex_unlock(&snd_ctl_led_mutex);
> > +		snd_card_unref(card);
> > +		return -ENXIO;
> > +	}
> > +	led = &snd_ctl_leds[group];
> > +repeat:
> > +	list_for_each_entry(lctl, &led->controls, list)
> > +		if (lctl->card == card) {
> > +			vd = &lctl->kctl->vd[lctl->index_offset];
> > +			vd->access &= ~group_to_access(group);
> > +			snd_ctl_led_ctl_destroy(lctl);
> > +			change = true;
> > +			goto repeat;
> > +		}
> > +	mutex_unlock(&snd_ctl_led_mutex);
> > +	if (change)
> > +		snd_ctl_led_set_state(NULL, group_to_access(group), NULL, 0);
> > +	snd_card_unref(card);
> > +	return 0;
> > +}
> > +
> >  static void snd_ctl_led_register(struct snd_card *card)
> >  {
> >  	struct snd_kcontrol *kctl;
> > @@ -264,10 +354,12 @@ static void snd_ctl_led_register(struct snd_card *card)
> >  		for (ioff = 0; ioff < kctl->count; ioff++)
> >  			snd_ctl_led_notify(card, SNDRV_CTL_EVENT_MASK_VALUE, kctl, ioff);
> >  	snd_ctl_led_refresh();
> > +	snd_ctl_led_sysfs_add(card);
> >  }
> >  
> >  static void snd_ctl_led_disconnect(struct snd_card *card)
> >  {
> > +	snd_ctl_led_sysfs_remove(card);
> >  	mutex_lock(&snd_ctl_led_mutex);
> >  	snd_ctl_led_card_valid[card->number] = false;
> >  	snd_ctl_led_clean(card);
> > @@ -349,8 +441,264 @@ static const struct attribute_group *snd_ctl_led_dev_attr_groups[] = {
> >  	NULL,
> >  };
> >  
> > +static char *find_eos(char *s)
> > +{
> > +	while (*s && *s != ',')
> > +		s++;
> > +	if (*s)
> > +		s++;
> > +	return s;
> > +}
> > +
> > +static char *parse_uint(char *s, unsigned int *val)
> > +{
> > +	unsigned long long res;
> > +	if (kstrtoull(s, 10, &res))
> > +		res = 0;
> > +	*val = res;
> > +	return find_eos(s);
> > +}
> > +
> > +static char *parse_string(char *s, char *val, size_t val_size)
> > +{
> > +	if (*s == '"' || *s == '\'') {
> > +		char c = *s;
> > +		s++;
> > +		while (*s && *s != c) {
> > +			if (val_size > 1) {
> > +				*val++ = *s;
> > +				val_size--;
> > +			}
> > +			s++;
> > +		}
> > +	} else {
> > +		while (*s && *s != ',') {
> > +			if (val_size > 1) {
> > +				*val++ = *s;
> > +				val_size--;
> > +			}
> > +			s++;
> > +		}
> > +	}
> > +	*val = '\0';
> > +	if (*s)
> > +		s++;
> > +	return s;
> > +}
> > +
> > +static char *parse_iface(char *s, unsigned int *val)
> > +{
> > +	if (!strncasecmp(s, "card", 4))
> > +		*val = SNDRV_CTL_ELEM_IFACE_CARD;
> > +	else if (!strncasecmp(s, "mixer", 5))
> > +		*val = SNDRV_CTL_ELEM_IFACE_MIXER;
> > +	return find_eos(s);
> > +}
> > +
> > +/*
> > + * These types of input strings are accepted:
> > + *
> > + *   unsigned integer - numid (equivaled to numid=UINT)
> > + *   string - basic mixer name (equivalent to iface=MIXER,name=STR)
> > + *   numid=UINT
> > + *   [iface=MIXER,][device=UINT,][subdevice=UINT,]name=STR[,index=UINT]
> > + */
> > +static ssize_t set_led_id(struct snd_ctl_led_card *led_card, const char *buf, size_t count,
> > +			  bool attach)
> > +{
> > +	char buf2[256], *s;
> > +	size_t len = max(sizeof(s) - 1, count);
> > +	struct snd_ctl_elem_id id;
> > +	int err;
> > +
> > +	strncpy(buf2, buf, len);
> > +	buf2[len] = '\0';
> > +	memset(&id, 0, sizeof(id));
> > +	id.iface = SNDRV_CTL_ELEM_IFACE_MIXER;
> > +	s = buf2;
> > +	while (*s) {
> > +		if (!strncasecmp(s, "numid=", 6)) {
> > +			s = parse_uint(s + 6, &id.numid);
> > +		} else if (!strncasecmp(s, "iface=", 6)) {
> > +			s = parse_iface(s + 6, &id.iface);
> > +		} else if (!strncasecmp(s, "device=", 7)) {
> > +			s = parse_uint(s + 7, &id.device);
> > +		} else if (!strncasecmp(s, "subdevice=", 10)) {
> > +			s = parse_uint(s + 10, &id.subdevice);
> > +		} else if (!strncasecmp(s, "name=", 5)) {
> > +			s = parse_string(s + 5, id.name, sizeof(id.name));
> > +		} else if (!strncasecmp(s, "index=", 6)) {
> > +			s = parse_uint(s + 6, &id.index);
> > +		} else if (s == buf2) {
> > +			while (*s) {
> > +				if (*s < '0' || *s > '9')
> > +					break;
> > +				s++;
> > +			}
> > +			if (*s == '\0')
> > +				parse_uint(buf2, &id.numid);
> > +			else {
> > +				for (; *s >= ' '; s++);
> > +				*s = '\0';
> > +				strlcpy(id.name, buf2, sizeof(id.name));
> > +			}
> > +			break;
> > +		}
> > +		if (*s == ',')
> > +			s++;
> > +	}
> > +
> > +	err = snd_ctl_led_set_id(led_card->number, &id, led_card->led->group, attach);
> > +	if (err < 0)
> > +		return err;
> > +
> > +	return count;
> > +}
> > +
> > +static ssize_t parse_attach(struct device *dev, struct device_attribute *attr,
> > +			    const char *buf, size_t count)
> > +{
> > +	struct snd_ctl_led_card *led_card = container_of(dev, struct snd_ctl_led_card, dev);
> > +	return set_led_id(led_card, buf, count, true);
> > +}
> > +
> > +static ssize_t parse_detach(struct device *dev, struct device_attribute *attr,
> > +			    const char *buf, size_t count)
> > +{
> > +	struct snd_ctl_led_card *led_card = container_of(dev, struct snd_ctl_led_card, dev);
> > +	return set_led_id(led_card, buf, count, false);
> > +}
> > +
> > +static ssize_t ctl_reset(struct device *dev, struct device_attribute *attr,
> > +			 const char *buf, size_t count)
> > +{
> > +	struct snd_ctl_led_card *led_card = container_of(dev, struct snd_ctl_led_card, dev);
> > +	int err;
> > +
> > +	if (count > 0 && buf[0] == '1') {
> > +		err = snd_ctl_led_reset(led_card->number, led_card->led->group);
> > +		if (err < 0)
> > +			return err;
> > +	}
> > +	return count;
> > +}
> > +
> > +static ssize_t ctl_list(struct device *dev,
> > +			struct device_attribute *attr, char *buf)
> > +{
> > +	struct snd_ctl_led_card *led_card = container_of(dev, struct snd_ctl_led_card, dev);
> > +	struct snd_card *card;
> > +	struct snd_ctl_led_ctl *lctl;
> > +	char *buf2 = buf;
> > +	size_t l;
> > +
> > +	card = snd_card_ref(led_card->number);
> > +	if (!card)
> > +		return -ENXIO;
> > +	down_read(&card->controls_rwsem);
> > +	mutex_lock(&snd_ctl_led_mutex);
> > +	if (snd_ctl_led_card_valid[led_card->number]) {
> > +		list_for_each_entry(lctl, &led_card->led->controls, list)
> > +			if (lctl->card == card) {
> > +				if (buf2 - buf > PAGE_SIZE - 16)
> > +					break;
> > +				if (buf2 != buf)
> > +					*buf2++ = ' ';
> > +				l = scnprintf(buf2, 15, "%u",
> > +						lctl->kctl->id.numid +
> > +							lctl->index_offset);
> > +				buf2[l] = '\0';
> > +				buf2 += l + 1;
> > +			}
> > +	}
> > +	mutex_unlock(&snd_ctl_led_mutex);
> > +	up_read(&card->controls_rwsem);
> > +	snd_card_unref(card);
> > +	return buf2 - buf;
> > +}
> > +
> > +static DEVICE_ATTR(attach, 0200, NULL, parse_attach);
> > +static DEVICE_ATTR(detach, 0200, NULL, parse_detach);
> > +static DEVICE_ATTR(reset, 0200, NULL, ctl_reset);
> > +static DEVICE_ATTR(list, 0444, ctl_list, NULL);
> > +
> > +static struct attribute *snd_ctl_led_card_attrs[] = {
> > +	&dev_attr_attach.attr,
> > +	&dev_attr_detach.attr,
> > +	&dev_attr_reset.attr,
> > +	&dev_attr_list.attr,
> > +	NULL,
> > +};
> > +
> > +static const struct attribute_group snd_ctl_led_card_attr_group = {
> > +	.attrs = snd_ctl_led_card_attrs,
> > +};
> > +
> > +static const struct attribute_group *snd_ctl_led_card_attr_groups[] = {
> > +	&snd_ctl_led_card_attr_group,
> > +	NULL,
> > +};
> > +
> >  static struct device snd_ctl_led_dev;
> >  
> > +static void snd_ctl_led_sysfs_add(struct snd_card *card)
> > +{
> > +	unsigned int group;
> > +	struct snd_ctl_led_card *led_card;
> > +	struct snd_ctl_led *led;
> > +	char link_name[32];
> > +
> > +	for (group = 0; group < MAX_LED; group++) {
> > +		led = &snd_ctl_leds[group];
> > +		led_card = kzalloc(sizeof(*led_card), GFP_KERNEL);
> > +		if (!led_card)
> > +			goto cerr2;
> > +		led_card->number = card->number;
> > +		led_card->led = led;
> > +		device_initialize(&led_card->dev);
> > +		if (dev_set_name(&led_card->dev, "card%d", card->number) < 0)
> > +			goto cerr;
> > +		led_card->dev.parent = &led->dev;
> > +		led_card->dev.groups = snd_ctl_led_card_attr_groups;
> > +		if (device_add(&led_card->dev))
> > +			goto cerr;
> > +		led->cards[card->number] = led_card;
> > +		snprintf(link_name, sizeof(link_name), "led-%s", led->name);
> > +		WARN(sysfs_create_link(&card->ctl_dev.kobj, &led_card->dev.kobj, link_name),
> > +			"can't create symlink to controlC%i device\n", card->number);
> > +		WARN(sysfs_create_link(&led_card->dev.kobj, &card->card_dev.kobj, "card"),
> > +			"can't create symlink to card%i\n", card->number);
> > +
> > +		continue;
> > +cerr:
> > +		put_device(&led_card->dev);
> > +cerr2:
> > +		printk(KERN_ERR "snd_ctl_led: unable to add card%d", card->number);
> > +		kfree(led_card);
> > +	}
> > +}
> > +
> > +static void snd_ctl_led_sysfs_remove(struct snd_card *card)
> > +{
> > +	unsigned int group;
> > +	struct snd_ctl_led_card *led_card;
> > +	struct snd_ctl_led *led;
> > +	char link_name[32];
> > +
> > +	for (group = 0; group < MAX_LED; group++) {
> > +		led = &snd_ctl_leds[group];
> > +		led_card = led->cards[card->number];
> > +		if (!led_card)
> > +			continue;
> > +		snprintf(link_name, sizeof(link_name), "led-%s", led->name);
> > +		sysfs_remove_link(&card->ctl_dev.kobj, link_name);
> > +		sysfs_remove_link(&led_card->dev.kobj, "card");
> > +		device_del(&led_card->dev);
> > +		kfree(led_card);
> > +		led->cards[card->number] = NULL;
> > +	}
> > +}
> > +
> >  /*
> >   * Control layer registration
> >   */
> > @@ -397,14 +745,24 @@ static int __init snd_ctl_led_init(void)
> >  static void __exit snd_ctl_led_exit(void)
> >  {
> >  	struct snd_ctl_led *led;
> > -	unsigned int group;
> > +	struct snd_card *card;
> > +	unsigned int group, card_number;
> >  
> > +	snd_ctl_disconnect_layer(&snd_ctl_led_lops);
> > +	for (card_number = 0; card_number < SNDRV_CARDS; card_number++) {
> > +		if (!snd_ctl_led_card_valid[card_number])
> > +			continue;
> > +		card = snd_card_ref(card_number);
> > +		if (card) {
> > +			snd_ctl_led_sysfs_remove(card);
> > +			snd_card_unref(card);
> > +		}
> > +	}
> >  	for (group = 0; group < MAX_LED; group++) {
> >  		led = &snd_ctl_leds[group];
> >  		device_del(&led->dev);
> >  	}
> >  	device_del(&snd_ctl_led_dev);
> > -	snd_ctl_disconnect_layer(&snd_ctl_led_lops);
> >  	snd_ctl_led_clean(NULL);
> >  }
> >  
> > 
> 