[alsa-devel] [PATCH 2/4] ALSA: dice: postpone card registration

[Takashi Iwai]

On Tue, 22 Dec 2015 14:45:41 +0100,
Takashi Sakamoto wrote:
> 
> Some models based on ASIC for Dice II series (STD, CP) change their
> hardware configurations after appearing on IEEE 1394 bus. This is due to
> interactions of boot loader (RedBoot), firmwares (eCos) and vendor's
> configurations. This causes current ALSA dice driver to get wrong
> information about the hardware's capability because its probe function
> runs just after detecting unit of the model.
> 
> As long as I investigated, it takes a bit time (less than 1 second) to load
> the firmware after bootstrap. Just after loaded, the driver can get
> information about the unit. Then the hardware is initialized according to
> vendor's configurations. After, the got information becomes wrong.
> Between bootstrap, firmware loading and post configuration, some bus resets
> are observed.
> 
> This commit offloads most processing of probe function into workqueue and
> schedules the workqueue after successive bus resets. This has an effect to
> get correct hardware information and avoid involvement to bus reset storm.
> 
> For code simplicity, this change effects all of Dice-based models, i.e.
> Dice II, Dice Jr., Dice Mini and Dice III. Due to the same reason, sound
> card instance is kept till card free function even if some errors are
> detected in the workqueue.
> 
> Signed-off-by: Takashi Sakamoto <o-takashi at sakamocchi.jp>
> ---
>  sound/firewire/dice/dice.c | 105 +++++++++++++++++++++++++++++++++------------
>  sound/firewire/dice/dice.h |   3 ++
>  2 files changed, 80 insertions(+), 28 deletions(-)
> 
> diff --git a/sound/firewire/dice/dice.c b/sound/firewire/dice/dice.c
> index 26271cc..afec02f 100644
> --- a/sound/firewire/dice/dice.c
> +++ b/sound/firewire/dice/dice.c
> @@ -18,6 +18,8 @@ MODULE_LICENSE("GPL v2");
>  #define WEISS_CATEGORY_ID	0x00
>  #define LOUD_CATEGORY_ID	0x10
>  
> +#define PROBE_DELAY_MS		(2 * MSEC_PER_SEC)
> +
>  static int check_dice_category(struct fw_unit *unit)
>  {
>  	struct fw_device *device = fw_parent_device(unit);
> @@ -185,17 +187,68 @@ static void dice_card_free(struct snd_card *card)
>  {
>  	struct snd_dice *dice = card->private_data;
>  
> +	/* The workqueue for registration uses the memory block. */
> +	cancel_work_sync(&dice->dwork.work);
> +
>  	snd_dice_stream_destroy_duplex(dice);
> +
>  	snd_dice_transaction_destroy(dice);
> +
>  	fw_unit_put(dice->unit);
>  
>  	mutex_destroy(&dice->mutex);
>  }
>  
> +static void do_registration(struct work_struct *work)
> +{
> +	struct snd_dice *dice = container_of(work, struct snd_dice, dwork.work);
> +	int err;
> +
> +	mutex_lock(&dice->mutex);
> +
> +	if (dice->card->shutdown || dice->probed)
> +		goto end;
> +
> +	err = snd_dice_transaction_init(dice);
> +	if (err < 0)
> +		goto end;
> +
> +	err = dice_read_params(dice);
> +	if (err < 0)
> +		goto end;
> +
> +	dice_card_strings(dice);
> +
> +	err = snd_dice_create_pcm(dice);
> +	if (err < 0)
> +		goto end;
> +
> +	err = snd_dice_create_midi(dice);
> +	if (err < 0)
> +		goto end;
> +
> +	err = snd_card_register(dice->card);
> +	if (err < 0)
> +		goto end;
> +
> +	dice->probed = true;
> +end:
> +	mutex_unlock(&dice->mutex);
> +
> +	/*
> +	 * It's a difficult work to manage a race condition between workqueue,
> +	 * unit event handlers and processes. The memory block for this card
> +	 * is released as the same way that usual sound cards are going to be
> +	 * released.
> +	 */
> +}
> +
>  static int dice_probe(struct fw_unit *unit, const struct ieee1394_device_id *id)
>  {
> +	struct fw_card *fw_card = fw_parent_device(unit)->card;
>  	struct snd_card *card;
>  	struct snd_dice *dice;
> +	unsigned long delay;
>  	int err;
>  
>  	err = check_dice_category(unit);
> @@ -205,29 +258,20 @@ static int dice_probe(struct fw_unit *unit, const struct ieee1394_device_id *id)
>  	err = snd_card_new(&unit->device, -1, NULL, THIS_MODULE,
>  			   sizeof(*dice), &card);
>  	if (err < 0)
> -		goto end;
> +		return err;
>  
>  	dice = card->private_data;
>  	dice->card = card;
>  	dice->unit = fw_unit_get(unit);
>  	card->private_free = dice_card_free;
> +	dev_set_drvdata(&unit->device, dice);
>  
>  	spin_lock_init(&dice->lock);
>  	mutex_init(&dice->mutex);
>  	init_completion(&dice->clock_accepted);
>  	init_waitqueue_head(&dice->hwdep_wait);
>  
> -	err = snd_dice_transaction_init(dice);
> -	if (err < 0)
> -		goto error;
> -
> -	err = dice_read_params(dice);
> -	if (err < 0)
> -		goto error;
> -
> -	dice_card_strings(dice);
> -
> -	err = snd_dice_create_pcm(dice);
> +	err = snd_dice_stream_init_duplex(dice);
>  	if (err < 0)
>  		goto error;
>  
> @@ -237,23 +281,13 @@ static int dice_probe(struct fw_unit *unit, const struct ieee1394_device_id *id)
>  
>  	snd_dice_create_proc(dice);
>  
> -	err = snd_dice_create_midi(dice);
> -	if (err < 0)
> -		goto error;
> -
> -	err = snd_dice_stream_init_duplex(dice);
> -	if (err < 0)
> -		goto error;
> -
> -	err = snd_card_register(card);
> -	if (err < 0) {
> -		snd_dice_stream_destroy_duplex(dice);
> -		goto error;
> -	}
> +	/* Register this sound card later. */
> +	INIT_DEFERRABLE_WORK(&dice->dwork, do_registration);
> +	delay = msecs_to_jiffies(PROBE_DELAY_MS) +
> +				fw_card->reset_jiffies - get_jiffies_64();
> +	schedule_delayed_work(&dice->dwork, delay);

Missing negative jiffies check?


>  
> -	dev_set_drvdata(&unit->device, dice);
> -end:
> -	return err;
> +	return 0;
>  error:
>  	snd_card_free(card);
>  	return err;
> @@ -263,13 +297,28 @@ static void dice_remove(struct fw_unit *unit)
>  {
>  	struct snd_dice *dice = dev_get_drvdata(&unit->device);
>  
> +	/* For a race condition of struct snd_card.shutdown. */
> +	mutex_lock(&dice->mutex);
> +
>  	/* No need to wait for releasing card object in this context. */
>  	snd_card_free_when_closed(dice->card);
> +
> +	mutex_unlock(&dice->mutex);
>  }
>  
>  static void dice_bus_reset(struct fw_unit *unit)
>  {
>  	struct snd_dice *dice = dev_get_drvdata(&unit->device);
> +	struct fw_card *fw_card = fw_parent_device(unit)->card;
> +	unsigned long delay;
> +
> +	/* Postpone a workqueue for deferred registration. */
> +	if (!dice->probed) {
> +		delay = msecs_to_jiffies(PROBE_DELAY_MS) -
> +				(get_jiffies_64() - fw_card->reset_jiffies);
> +		mod_delayed_work(dice->dwork.wq, &dice->dwork, delay);
> +		return;

No protection for race here?


Takashi