linux-kernel - Re: [PATCH v2 2/7] acpi: utils: Add function to fetch dependent acpi

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Message-ID: <YAU57AEmtBHuz6T8@pendragon.ideasonboard.com>
Date:   Mon, 18 Jan 2021 09:34:04 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Daniel Scally <djrscally@...il.com>
Cc:     linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
        linux-gpio@...r.kernel.org, linux-i2c@...r.kernel.org,
        platform-driver-x86@...r.kernel.org, devel@...ica.org,
        rjw@...ysocki.net, lenb@...nel.org, andy@...nel.org,
        mika.westerberg@...ux.intel.com, linus.walleij@...aro.org,
        bgolaszewski@...libre.com, wsa@...nel.org, lee.jones@...aro.org,
        hdegoede@...hat.com, mgross@...ux.intel.com,
        robert.moore@...el.com, erik.kaneda@...el.com,
        sakari.ailus@...ux.intel.com, andriy.shevchenko@...ux.intel.com,
        kieran.bingham@...asonboard.com
Subject: Re: [PATCH v2 2/7] acpi: utils: Add function to fetch dependent
 acpi_devices

Hi Daniel,

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@...il.com>
> ---
> 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)
>  }
>  EXPORT_SYMBOL(acpi_dev_present);
>  
> +/**
> + * 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;
> +}
> +EXPORT_SYMBOL(acpi_dev_get_next_dep_dev);

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@...asonboard.com>

> +
>  /**
>   * 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 *

-- 
Regards,

Laurent Pinchart