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Date:   Fri, 30 Jun 2023 19:26:49 +0200
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Subject: Re: [PATCH v5 09/10] acpi/nfit: Move handler installing logic to
 driver
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To:     Dan Williams <dan.j.williams@intel.com>,
        <linux-acpi@vger.kernel.org>
CC:     <rafael@kernel.org>, <vishal.l.verma@intel.com>, <lenb@kernel.org>,
        <dave.jiang@intel.com>, <ira.weiny@intel.com>,
        <rui.zhang@intel.com>, <linux-kernel@vger.kernel.org>,
        <nvdimm@lists.linux.dev>,
        "Rafael J . Wysocki" <rafael.j.wysocki@intel.com>
References: <20230616165034.3630141-1-michal.wilczynski@intel.com>
 <20230616165034.3630141-10-michal.wilczynski@intel.com>
 <649def832ce1f_11e68529491@dwillia2-xfh.jf.intel.com.notmuch>
 <81dbbc8f-fc05-754d-56bf-5e74169b8dc8@intel.com>
 <649f0ea3bfae4_11e685294f2@dwillia2-xfh.jf.intel.com.notmuch>
From:   "Wilczynski, Michal" <michal.wilczynski@intel.com>
In-Reply-To: <649f0ea3bfae4_11e685294f2@dwillia2-xfh.jf.intel.com.notmuch>
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On 6/30/2023 7:19 PM, Dan Williams wrote:
> Wilczynski, Michal wrote:
>>
>> On 6/29/2023 10:54 PM, Dan Williams wrote:
>>> Michal Wilczynski wrote:
>>>> Currently logic for installing notifications from ACPI devices is
>>>> implemented using notify callback in struct acpi_driver. Preparations
>>>> are being made to replace acpi_driver with more generic struct
>>>> platform_driver, which doesn't contain notify callback. Furthermore
>>>> as of now handlers are being called indirectly through
>>>> acpi_notify_device(), which decreases performance.
>>>>
>>>> Call acpi_dev_install_notify_handler() at the end of .add() callback.
>>>> Call acpi_dev_remove_notify_handler() at the beginning of .remove()
>>>> callback. Change arguments passed to the notify function to match with
>>>> what's required by acpi_install_notify_handler(). Remove .notify
>>>> callback initialization in acpi_driver.
>>>>
>>>> Suggested-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>>>> Signed-off-by: Michal Wilczynski <michal.wilczynski@intel.com>
>>>> ---
>>>>  drivers/acpi/nfit/core.c | 24 ++++++++++++++++++------
>>>>  1 file changed, 18 insertions(+), 6 deletions(-)
>>>>
>>>> diff --git a/drivers/acpi/nfit/core.c b/drivers/acpi/nfit/core.c
>>>> index 95930e9d776c..a281bdfee8a0 100644
>>>> --- a/drivers/acpi/nfit/core.c
>>>> +++ b/drivers/acpi/nfit/core.c
>>>> @@ -3312,11 +3312,13 @@ void acpi_nfit_shutdown(void *data)
>>>>  }
>>>>  EXPORT_SYMBOL_GPL(acpi_nfit_shutdown);
>>>>  
>>>> -static void acpi_nfit_notify(struct acpi_device *adev, u32 event)
>>>> +static void acpi_nfit_notify(acpi_handle handle, u32 event, void *data)
>>>>  {
>>>> -	device_lock(&adev->dev);
>>>> -	__acpi_nfit_notify(&adev->dev, adev->handle, event);
>>>> -	device_unlock(&adev->dev);
>>>> +	struct acpi_device *device = data;
>>>> +
>>>> +	device_lock(&device->dev);
>>>> +	__acpi_nfit_notify(&device->dev, handle, event);
>>>> +	device_unlock(&device->dev);
>>>>  }
>>>>  
>>>>  static int acpi_nfit_add(struct acpi_device *adev)
>>>> @@ -3375,12 +3377,23 @@ static int acpi_nfit_add(struct acpi_device *adev)
>>>>  
>>>>  	if (rc)
>>>>  		return rc;
>>>> -	return devm_add_action_or_reset(dev, acpi_nfit_shutdown, acpi_desc);
>>>> +
>>>> +	rc = devm_add_action_or_reset(dev, acpi_nfit_shutdown, acpi_desc);
>>>> +	if (rc)
>>>> +		return rc;
>>>> +
>>>> +	return acpi_dev_install_notify_handler(adev,
>>>> +					       ACPI_DEVICE_NOTIFY,
>>>> +					       acpi_nfit_notify);
>>>>  }
>>>>  
>>>>  static void acpi_nfit_remove(struct acpi_device *adev)
>>>>  {
>>>>  	/* see acpi_nfit_unregister */
>>>> +
>>>> +	acpi_dev_remove_notify_handler(adev,
>>>> +				       ACPI_DEVICE_NOTIFY,
>>>> +				       acpi_nfit_notify);
>>> Please use devm to trigger this release rather than making
>>> acpi_nfit_remove() contain any logic.
>> I think adding separate devm action to remove event handler is not
>> necessary. I'll put the removal in the beggining of acpi_nfit_shutdown() if you
>> don't object.
> How do you plan to handle an acpi_dev_install_notify_handler() failure?
> acpi_nfit_shutdown() will need to have extra logic to know that it can
> skip acpi_dev_remove_notify_handler() in some cases and not other..
> Maybe it is ok to remove a handler that was never installed, but I would
> rather not go look that up. A devm callback for
> acpi_dev_remove_notify_handler() avoids that.

Sure, I looked at the code and it seems to me that trying to remove a callback that doesn't
exist shouldn't cause any problems. But maybe it's not very elegant and we shouldn't rely
on that behavior.

Will add separate devm action for that then.