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

[Marek Szyprowski]

On 18.06.2026 14:58, Marek Szyprowski wrote:
> On 18.06.2026 13:22, Richard Fitzgerald wrote:
>> On 17/6/26 15:10, Marek Szyprowski wrote:
>>> 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 at 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
>>>
>> Where in device_link_add() does it fail?
>>
> It fails the following check at drivers/base/core.c line 766:
>
>        if (!device_pm_initialized(supplier)
>             || (!(flags & DL_FLAG_SYNC_STATE_ONLY) &&
>                   device_is_dependent(consumer, supplier))) {
>                 link = NULL;
>                 goto out;
>         }
>
> because device_is_dependent(consumer, supplier) is true for fef00700.hdmi and
> hdmi-audio-codec.1.auto.
This hack fixes VC4 probing (I'm aware that drivers/base/core.c change is not
acceptable):

diff --git a/drivers/base/core.c b/drivers/base/core.c
index bd2ddf2aab50..03e0909d5d68 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -300,7 +300,7 @@ bool device_link_flag_is_sync_state_only(u32 flags)
  * Check if @target depends on @dev or any device dependent on it (its child or
  * its consumer etc).  Return 1 if that is the case or 0 otherwise.
  */
-static int device_is_dependent(struct device *dev, void *target)
+int device_is_dependent(struct device *dev, void *target)
 {
        struct device_link *link;
        int ret;
@@ -330,6 +330,7 @@ static int device_is_dependent(struct device *dev, void *target)
        }
        return ret;
 }
+EXPORT_SYMBOL_GPL(device_is_dependent);

 static void device_link_init_status(struct device_link *link,
                                    struct device *consumer,
diff --git a/sound/soc/soc-core.c b/sound/soc/soc-core.c
index ac9b2269c26e..ba70befea0e8 100644
--- a/sound/soc/soc-core.c
+++ b/sound/soc/soc-core.c
@@ -2165,6 +2165,8 @@ static void snd_soc_unbind_card(struct snd_soc_card *card)
        }
 }

+extern int device_is_dependent(struct device *dev, void *target);
+
 static int snd_soc_bind_card(struct snd_soc_card *card)
 {
        struct snd_soc_pcm_runtime *rtd;
@@ -2304,7 +2306,8 @@ static int snd_soc_bind_card(struct snd_soc_card *card)
                if (card->dev == component->dev)
                        continue;

-               if (!device_link_add(card->dev, component->dev, DL_FLAG_STATELESS)) {
+               if (!device_is_dependent(card->dev, component->dev) &&
+                   !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;


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