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

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

On 18.06.2026 15:12, Richard Fitzgerald wrote:
> On 18/6/26 13:58, 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@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.
>>
>>
>> Best regards
>
> Is the machine driver the parent of the codec driver?


Yes, so this change fixes the issue:

diff --git a/sound/soc/soc-core.c b/sound/soc/soc-core.c
index ac9b2269c26e..5e00ad0bc7cf 100644
--- a/sound/soc/soc-core.c
+++ b/sound/soc/soc-core.c
@@ -2304,7 +2304,8 @@ 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 (component->dev->parent != card->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