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

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

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