Re: [PATCH v2 2/7] acpi: utils: Add function to fetch dependent acpi_devices
From: Laurent Pinchart
Date: Mon Jan 18 2021 - 02:35:35 EST
Thank you for the patch.
On Mon, Jan 18, 2021 at 12:34:23AM +0000, Daniel Scally wrote:
> In some ACPI tables we encounter, devices use the _DEP method to assert
> a dependence on other ACPI devices as opposed to the OpRegions that the
> specification intends. We need to be able to find those devices "from"
> the dependee, so add a function to parse all ACPI Devices and check if
> the include the handle of the dependee device in their _DEP buffer.
> Signed-off-by: Daniel Scally <djrscally@xxxxxxxxx>
> Changes in v2:
> - Used acpi_lpss_dep() as Andy suggested.
> drivers/acpi/utils.c | 34 ++++++++++++++++++++++++++++++++++
> include/acpi/acpi_bus.h | 2 ++
> 2 files changed, 36 insertions(+)
> diff --git a/drivers/acpi/utils.c b/drivers/acpi/utils.c
> index 78b38775f18b..ec6a2406a886 100644
> --- a/drivers/acpi/utils.c
> +++ b/drivers/acpi/utils.c
> @@ -831,6 +831,18 @@ bool acpi_lpss_dep(struct acpi_device *adev, acpi_handle handle)
> return false;
> +static int acpi_dev_match_by_dep(struct device *dev, const void *data)
> + struct acpi_device *adev = to_acpi_device(dev);
> + const struct acpi_device *dependee = data;
> + acpi_handle handle = dependee->handle;
> + if (acpi_lpss_dep(adev, handle))
> + return 1;
> + return 0;
I think I'd move this just before acpi_dev_get_next_dep_dev() to keep
the two together.
> * acpi_dev_present - Detect that a given ACPI device is present
> * @hid: Hardware ID of the device.
> @@ -866,6 +878,28 @@ bool acpi_dev_present(const char *hid, const char *uid, s64 hrv)
> + * acpi_dev_get_next_dep_dev - Return next ACPI device dependent on input dev
Maybe acpi_dev_get_next_dependent_dev() ? "dep" could mean either
dependent or dependency.
> + * @adev: Pointer to the dependee device
> + * @prev: Pointer to the previous dependent device (or NULL for first match)
> + *
> + * Return the next ACPI device which declares itself dependent on @adev in
> + * the _DEP buffer.
> + *
> + * The caller is responsible to call put_device() on the returned device.
> + */
> +struct acpi_device *acpi_dev_get_next_dep_dev(struct acpi_device *adev,
> + struct acpi_device *prev)
> + struct device *start = prev ? &prev->dev : NULL;
> + struct device *dev;
> + dev = bus_find_device(&acpi_bus_type, start, adev, acpi_dev_match_by_dep);
Having to loop over all ACPI devices is quite inefficient, but if we
need a reverse lookup, we don't really have a choice. We could create a
reverse map, but I don't think it's worth it.
> + return dev ? to_acpi_device(dev) : NULL;
I would have used EXPORT_SYMBOL_GPL. I'm not sure what the policy is in
the ACPI subsystem, and it's also a personal choice.
Reviewed-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
> * acpi_dev_get_next_match_dev - Return the next match of ACPI device
> * @adev: Pointer to the previous acpi_device matching this @hid, @uid and @hrv
> diff --git a/include/acpi/acpi_bus.h b/include/acpi/acpi_bus.h
> index 02a716a0af5d..33deb22294f2 100644
> --- a/include/acpi/acpi_bus.h
> +++ b/include/acpi/acpi_bus.h
> @@ -683,6 +683,8 @@ static inline bool acpi_device_can_poweroff(struct acpi_device *adev)
> bool acpi_dev_hid_uid_match(struct acpi_device *adev, const char *hid2, const char *uid2);
> +struct acpi_device *
> +acpi_dev_get_next_dep_dev(struct acpi_device *adev, struct acpi_device *prev);
> struct acpi_device *
> acpi_dev_get_next_match_dev(struct acpi_device *adev, const char *hid, const char *uid, s64 hrv);
> struct acpi_device *