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

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Date:   Mon, 18 Jan 2021 08:37:03 +0000
From:   Daniel Scally <djrscally@...il.com>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.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

Morning Laurent

On 18/01/2021 07:34, Laurent Pinchart wrote:
> 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.


Will do

>
>>  /**
>>   * 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.


Yes, good point, I agree.

>
>> + * @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.
EXPORT_SYMBOL_GPL would be my usual choice, but the other functions in
the file all use EXPORT_SYMBOL, so I assumed there was some policy that
that be used (since basically everywhere else I've touched in the kernel
so far defaults to the GPL version)
>
> Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>

Thanks!

>
>> +
>>  /**
>>   * 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 *