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

[Richard Fitzgerald <rf@opensource.cirrus.com>]

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?