Re: [PATCH v2] ASoC: soc-core: Create device_link to ensure correct suspend order

[Marek Szyprowski <m.szyprowski@samsung.com>]

Dear All,

On 11.06.2026 13:08, Richard Fitzgerald wrote:
> In snd_soc_bind_card() create a device_link from card to all components
> to ensure correct order of system_suspend. The card is the consumer and
> the components are the supplier, so that the card will system_suspend
> before any of the components.
>
> The PM core will normally system_suspend drivers in the opposite order
> that they registered. This ensures children are suspended before their
> parents, for example users of a bus driver should suspend before the bus
> driver suspends.
>
> For ASoC, snd_soc_suspend() shuts down any active audio, which requires
> that the components are still able to communicate with their hardware.
> Previously there was nothing to ensure this ordering, because there is
> (usually) no relationship between a machine driver and component drivers.
> If the machine driver registered before the codec drivers, the codec
> drivers would be suspended before the machine driver snd_soc_suspend()
> runs, so that ASoC is attempting to stop audio on a driver that has
> already suspended.
>
> Creating a device_link is safe if there is already a device_link between
> those devices because of multiple components sharing the same dev.
> device_link_add() kernel doc says:
>
>  "if a device link between the given @consumer and @supplier pair
>   exists already when this function is called for them, the existing link
>   will be returned regardless of its current type and status ...
>   The caller of this function is then expected to treat
>   the link as though it has just been created, so (in particular) if
>   DL_FLAG_STATELESS was passed in @flags, the link needs to be released
>   explicitly when not needed any more"
>
> For the same reason it is safe if the codec driver or machine driver
> later call device_link_add() to create a link between the same two
> devices.
>
> (I have tested creating multiple links between the card->dev and a
> component->dev and did not encounter any problems with suspend/resume or
> module unloading.)
>
> The DL_FLAG_AUTOREMOVE_* flags assume that they are being called from
> the probe() function of that device. This isn't guaranteed in ASoC card
> binding because of deferred binding. The exact behavior and consequences
> of the DL_FLAG_AUTOREMOVE_* are also unclear from the documentation.
> So DL_FLAG_STATELESS is used for safety, and the links are removed
> explicitly when the card unbinds or if the bind fails.
>
> Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
> ---


This patch landed recently in linux-next as commit 0f54ce994b23 ("ASoC:
soc-core: Create device_link to ensure correct suspend order"). In my
tests I found that it breaks probing of VC4 DRM subsystem on Raspberry Pi
3 and 4 boards due to an issue with hdmi-audio-codec:

# dmesg | grep vc4
vc4-drm gpu: bound fe400000.hvs (ops vc4_hvs_ops [vc4])
vc4_hdmi fef00700.hdmi: Failed to create device link to hdmi-audio-codec.1.auto
vc4_hdmi fef00700.hdmi: error -EINVAL: Could not register sound card
vc4-drm gpu: failed to bind fef00700.hdmi (ops vc4_hdmi_ops [vc4]): -22
vc4-drm gpu: adev bind failed: -22
vc4-drm gpu: probe with driver vc4-drm failed with error -22


> for-next
>
> Changes in V2:
> - Use DL_FLAG_STATELESS to avoid unclear/unstated behavior of the
>   DL_FLAG_AUTOREMOVE_* flags.
>
> - Skip creating a device link for a component that is the same device
>   as the card.
>
>  sound/soc/soc-core.c | 46 +++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 45 insertions(+), 1 deletion(-)
>
> diff --git a/sound/soc/soc-core.c b/sound/soc/soc-core.c
> index b8c9ddfc4490..ac9b2269c26e 100644
> --- a/sound/soc/soc-core.c
> +++ b/sound/soc/soc-core.c
> @@ -2138,10 +2138,29 @@ static void soc_cleanup_card_resources(struct snd_soc_card *card)
>  	}
>  }
>  
> +static void snd_soc_remove_device_links(struct snd_soc_card *card,
> +					struct snd_soc_component *stop_at)
> +{
> +	struct snd_soc_component *component;
> +
> +	for_each_card_components(card, component) {
> +		if (card->dev == component->dev)
> +			continue;
> +
> +		device_link_remove(card->dev, component->dev);
> +
> +		if (component == stop_at)
> +			return;
> +	}
> +}
> +
>  static void snd_soc_unbind_card(struct snd_soc_card *card)
>  {
>  	if (snd_soc_card_is_instantiated(card)) {
>  		card->instantiated = false;
> +
> +		snd_soc_remove_device_links(card, NULL);
> +
>  		soc_cleanup_card_resources(card);
>  	}
>  }
> @@ -2151,6 +2170,7 @@ static int snd_soc_bind_card(struct snd_soc_card *card)
>  	struct snd_soc_pcm_runtime *rtd;
>  	struct snd_soc_component *component;
>  	struct snd_soc_dapm_context *dapm = snd_soc_card_to_dapm(card);
> +	struct snd_soc_component *last_devlinked_component = NULL;
>  	int ret;
>  
>  	snd_soc_card_mutex_lock_root(card);
> @@ -2275,6 +2295,25 @@ static int snd_soc_bind_card(struct snd_soc_card *card)
>  		}
>  	}
>  
> +	/*
> +	 * Add device_link from card to component so that system_suspend
> +	 * will be done in the correct order. The card must suspend first
> +	 * to stop audio activity before the components suspend.
> +	 */
> +	for_each_card_components(card, component) {
> +		if (card->dev == component->dev)
> +			continue;
> +
> +		if (!device_link_add(card->dev, component->dev, DL_FLAG_STATELESS)) {
> +			dev_warn(card->dev, "Failed to create device link to %s\n",
> +				 dev_name(component->dev));
> +			ret = -EINVAL;
> +			goto probe_end;
> +		}
> +
> +		last_devlinked_component = component;
> +	}
> +
>  	ret = snd_soc_card_late_probe(card);
>  	if (ret < 0)
>  		goto probe_end;
> @@ -2303,8 +2342,13 @@ static int snd_soc_bind_card(struct snd_soc_card *card)
>  			pinctrl_pm_select_sleep_state(component->dev);
>  
>  probe_end:
> -	if (ret < 0)
> +	if (ret < 0) {
> +		if (last_devlinked_component)
> +			snd_soc_remove_device_links(card, last_devlinked_component);
> +
>  		soc_cleanup_card_resources(card);
> +	}
> +
>  	if (ret == -EPROBE_DEFER) {
>  		list_add(&card->list, &unbind_card_list);
>  		ret = 0;

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland