Date:   Mon, 4 Jan 2021 21:58:09 +0100
From:   Hans de Goede <hdegoede@...hat.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Jiaxun Yang <jiaxun.yang@...goat.com>,
        Platform Driver <platform-driver-x86@...r.kernel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>,
        Mark Gross <mgross@...ux.intel.com>,
        Ike Panhc <ike.pan@...onical.com>,
        Mark Pearson <markpearson@...ovo.com>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/2] IdeaPad platform profile support

Hi,

On 1/4/21 9:33 PM, Rafael J. Wysocki wrote:
> On Mon, Jan 4, 2021 at 3:36 PM Hans de Goede <hdegoede@...hat.com> wrote:
>>
>> Hi,
>>
>> On 1/1/21 1:56 PM, Jiaxun Yang wrote:
>>> Tested on Lenovo Yoga-14SARE Chinese Edition.
>>>
>>> Jiaxun Yang (2):
>>>   ACPI: platform-profile: Introduce data parameter to handler
>>>   platform/x86: ideapad-laptop: DYTC Platform profile support
>>>
>>>  drivers/acpi/platform_profile.c       |   4 +-
>>>  drivers/platform/x86/Kconfig          |   1 +
>>>  drivers/platform/x86/ideapad-laptop.c | 281 ++++++++++++++++++++++++++
>>>  include/linux/platform_profile.h      |   5 +-
>>>  4 files changed, 287 insertions(+), 4 deletions(-)
>>
>>
>> Thank you for your series, unfortunately the
>> "ACPI: platform-profile: Introduce data parameter to handler"
>> patch causes a conflict with the pending:
>> "[PATCH v8 3/3] platform/x86: thinkpad_acpi: Add platform profile support"
>> patch.
>>
>> But I do agree that adding that data parameter makes sense, so
>> it might be best to merge:
>>
>> "ACPI: platform-profile: Introduce data parameter to handler"
>>
>> First and then rebase the thinkpad_acpi patch on top.
>>
>> Rafael, do you think you could add:
>>
>> "ACPI: platform-profile: Introduce data parameter to handler"
>>
>> To the 2 ACPI: platform-profile patches which you already have pending for 5.11-rc# ?
> 
> I'm not sure why that patch is needed at all, because whoever
> registers a platform profile handler needs to have access to the
> original handler object anyway.

True, I was actually thinking that instead of the data argument, we might
pass a pointer to the original handler object like this:

@@ -64,7 +64,7 @@ static ssize_t platform_profile_show(struct device *dev,
 		return -ENODEV;
 	}
 
-	err = cur_profile->profile_get(&profile);
+	err = cur_profile->profile_get(cur_profile, &profile);
 	mutex_unlock(&profile_lock);
 	if (err)
 		return err;

And then the driver which has registered the cur_profile, can get to
its own data by using container of on the cur_profile pointer.

With the code currently in your bleeding-edge branch, there is no way
for any driver-code to get to its own (possibly/likely dynamically
allocated) driver-data struct.

E.g. a typical driver using only dynamic data tied to device_get_drvdata,
might have this:

struct driver_data {
	...
	struct platform_profile_handler profile_handler;
	...
};

int probe(...) {
	struct driver_data *my_data;

	my_data = devm_kzalloc(dev, sizeof(*my_data), GFP_KERNEL);

	...

	ret = platform_profile_register(&my_data->profile_handler);
	...
}

And with the change which I suggest above would then be able to
get the struct driver_data *my_data back from the profile_get callback by
using container_of on the struct platform_profile_handler *profile_handler
argument added to the profile_get callback.

I know that the platform_profile stuff is intended to only have a
single provider, so this could use global variables, but some
drivers which may be a provider use 0 global variables (other then
module_params) atm and it would be a lot cleaner from the pov
of the design of these drivers to be able to do something like the
pseudo code above. Which is why I added my Reviewed-by to patch 1/2
of the series from this thread.

Patch 1/2 does use a slightly different approach then I suggest above,
thinking more about this it would be cleaner IMHO to just pass the
cur_profile pointer to the callbacks as the pseudo-code patch which I
wrote above does. Drivers which use globals can then just ignore
the extra argument (and keep the platform_profile_handler struct const)
where as drivers which use dynamic allocation can embed the struct in
their driver's data-struct.

> Also, on a somewhat related note, I'm afraid that it may not be a good
> idea to push this series for 5.11-rc in the face of recent objections
> against new material going in after the merge window.

That is fine with me, since this did not make rc1 (nor rc2) I'm not entirely
comfortable with sending out a late pull-req for the pdx86 side of this
either, so lets postpone this to 5.12 (sorry Mark).

Rafael, once we have the discussion with the passing a pointer back to
the drivers data thing resolved (and a patch merged for that if we go
that route) can you provide me with an immutable branch to merge into
pdx86/for-next so that I can then merge the pdx86 bits on top ?

Note this does not need to be done right now around say rc4 would be fine,
so that we have some time for the patches currently in bleeding-edge to
settle a bit.

Regards,

Hans

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