On Thu, 27 Nov 2025 09:29:03 +0100, Greg KH <[email protected]> said:
> On Wed, Nov 26, 2025 at 02:13:03PM +0100, Bartosz Golaszewski wrote:
>> The logical thing to do would be to use "device_is_dependent()" but
>> this thread makes me think that won't fly.
>>
>> What should I do? What's the "correct" way of checking if two devices
>> are linked? I assume that fiddling with the supplier/consumer lists in
>> struct device is not it.
>
> fiddling with those lists is what device_is_dependent() does, but no,
> you really don't want to be doing that either manually or by calling
> this function.
>
> Who is creating this "link"? Can't that caller tell the gpio core this
> relationship at the same time as you are wanting to keep track of it
> too?
>
The link would be created in reset core.
Let's consider the following:
GPIO Consumer A ---> reset-gpio ---> |
| GPIO Controller pin X
GPIO Consumer B -------------------> |
The GPIO core will scan the device tree and realize that A and B share the
same pin. The reset-gpio device is not described in firmware, it will be
created only when A requests a reset control. When it, on behalf of consumer A,
requests pin X, GPIO core can not associate the link between consumer A and
pin X with the link between reset-gpio and pin X because there's no such
reference in firmware nodes between consumer A and reset-gpio. To GPIO, these
are two separate references to the same pin. Only reset core knows about A
being the consumer of reset-gpio.
We could add a function in reset like:
struct device *reset_gpio_to_reset_device(struct device *dev);
which would return the actual consumer of pin X for a device we identified as
reset-gpio (for instance: with device_is_compatible(dev, "reset-gpio")) but
that would be adding a symbol for a corner case and a single user and for
which the relevant information already exists and could easily be retrieved
from existing device links.
I hope that explains it better.
To answer your question: the caller can't tell GPIO about this relationship,
GPIO would have to ask reset about it but having a dedicated symbol for this
doesn't really sound like the best approach.
Bartosz
