linux-kernel - Re: [RFC PATCH v2] platform/x86/fujitsu-laptop: Add battery charge control support

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Message-ID: <Zb2GMCSIz1MuWpQZ@N>
Date: Sat, 03 Feb 2024 00:17:58 +0000
From: Szilard Fabian <szfabian@...emarch.art>
To: Armin Wolf <W_Armin@....de>
Cc: hdegoede@...hat.com, ilpo.jarvinen@...ux.intel.com, jwoithe@...t42.net, linux-kernel@...r.kernel.org, platform-driver-x86@...r.kernel.org
Subject: Re: [RFC PATCH v2] platform/x86/fujitsu-laptop: Add battery charge control support

Hello,

On Tue, Jan 30, 2024 at 03:02:09AM +0100, Armin Wolf wrote:
> Am 29.01.24 um 19:00 schrieb Szilard Fabian:
> > +
> > +	return sprintf(buf, "%d\n", status);
> > +}
> > +
> > +static DEVICE_ATTR_RW(charge_control_end_threshold);
> > +
> > +/* ACPI battery hook */
> > +
> > +static int fujitsu_battery_add(struct power_supply *battery,
> > +			       struct acpi_battery_hook *hook)
> > +{
> > +	/* Check if there is an existing FUJ02E3 ACPI device. */
> > +	if (fext == NULL)
> > +		return -ENODEV;
> 
> Can you put the struct acpi_battery_hook into the struct fujitsu_laptop
> and then use container_of() to retrieve the ACPI device from there?
> The dell-wmi-ddv driver does something similar.
> 
> This would guarantee that the battery hook always accesses the correct ACPI device
> and you could drop this check.
> 
> > +
> > +	/*
> > +	 * Check if the S006 0x21 method exists by trying to get the current
> > +	 * battery charge limit.
> > +	 */
> > +	int s006_cc_return;
> > +	s006_cc_return = call_fext_func(fext, FUNC_S006_METHOD,
> > +					CHARGE_CONTROL_RW, 0x21, 0x0);
> > +	if (s006_cc_return == UNSUPPORTED_CMD)
> > +		return -ENODEV;
> 
> Maybe this check should be done once during probe?
What about the following scenario?
- Put a bool into the struct fujitsu_laptop to store information about the
  machine's charge control ability.
- The S006 0x21 method check with `battery_hook_register` gets moved into
  an 'init function'. In that 'init function' the bool gets set accordingly.
- `battery_hook_unregister` gets moved into an 'exit function', where the
  bool gets read and when it's false nothing happens.
- `fext` check gets removed from `fujitsu_battery_add` because it's
  redundant (more about that later).
- The 'init function' gets called in `acpi_fujitsu_laptop_add` and the 'exit
  function' gets called in `acpi_fujitsu_laptop_remove`.

With that scenario the code could be a little bit clearer in my opinion.
And it is possible to drop the `fext` check because if the FUJ02E3 ACPI
device exists `fext` gets set in the `acpi_fujitsu_laptop_add` function with
an error check.
(And the `fujitsu_battery_add` `fext` check was already redundant because
`battery_hook_register` got called in `acpi_fujitsu_laptop_add`. `fext`
gets set in the same function, and there is an error check already.)

Thanks,
Szilard