Re: [PATCH] platform/x86: thinkpad_acpi: add adaptive_kbd_modes parameter

From: "Bjørn Mork" <bjorn@mork.no>
To: Eric Wong <e@80x24.org>
Cc: Henrique de Moraes Holschuh <ibm-acpi@hmh.eng.br>,
	Shuduo Sang <shuduo.sang@canonical.com>,
	Darren Hart <dvhart@infradead.org>,
	Andy Shevchenko <andy@infradead.org>,
	linux-kernel@vger.kernel.org,
	ibm-acpi-devel@lists.sourceforge.net,
	platform-driver-x86@vger.kernel.org
Subject: Re: [PATCH] platform/x86: thinkpad_acpi: add adaptive_kbd_modes parameter
Date: Sun, 25 Nov 2018 16:41:15 +0100	[thread overview]
Message-ID: <87zhtx17xg.fsf@miraculix.mork.no> (raw)
In-Reply-To: <20181125144441.xpwuov2i7lab3agh@dcvr> (Eric Wong's message of "Sun, 25 Nov 2018 14:44:41 +0000")

Eric Wong <e@80x24.org> writes:
> Bjørn Mork <bjorn@mork.no> wrote:
>
>> And then I believe you have a busy loop here:
>> 
>> > @@ -3815,20 +3838,20 @@ static int adaptive_keyboard_set_mode(int new_mode)
>> >  
>> >  static int adaptive_keyboard_get_next_mode(int mode)
>> >  {
>> > -	size_t i;
>> > -	size_t max_mode = ARRAY_SIZE(adaptive_keyboard_modes) - 1;
>> > -
>> > -	for (i = 0; i <= max_mode; i++) {
>> > -		if (adaptive_keyboard_modes[i] == mode)
>> > -			break;
>> > -	}
>> > +	int max_mode = fls(adaptive_kbd_modes);
>> > +	int new_mode = mode >= max_mode ? HOME_MODE : mode + 1;
>> >  
>> > -	if (i >= max_mode)
>> > -		i = 0;
>> > -	else
>> > -		i++;
>> > +	/* make sure the new mode is allowed by the user */
>> > +	while (!(adaptive_kbd_modes & (1 << new_mode))) {
>> > +		new_mode++;
>> > +		if (new_mode > max_mode)
>> > +			new_mode = HOME_MODE;
>> >  
>> > -	return adaptive_keyboard_modes[i];
>> > +		/* maybe the user disabled all other modes: */
>> > +		if (new_mode == mode)
>> > +			return mode;
>> > +	}
>> > +	return new_mode;
>> >  }
>
> Not a busy loop, since new_mode will reset at HOME_MODE (0)
> and then it'll hit "new_mode == mode" and remain locked in
> to the current mode.

Right.  I see it now.  Thanks for explaining.

I guess I was expecting a complete loop bypass ala

  if (!max_mode)
     return mode:

but your solution will of course work just as fine.

Bjørn