linux-kernel - Re: [PATCH v2 1/2] platform/x86: asus-wmi: Call led hw

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Date:   Tue, 19 Jun 2018 15:09:10 +0800
From:   Chris Chiu <chiu@...lessm.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Corentin Chary <corentin.chary@...il.com>,
        Darren Hart <dvhart@...radead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Platform Driver <platform-driver-x86@...r.kernel.org>,
        acpi4asus-user <acpi4asus-user@...ts.sourceforge.net>,
        Hans de Goede <hdegoede@...hat.com>,
        Linux Upstreaming Team <linux@...lessm.com>
Subject: Re: [PATCH v2 1/2] platform/x86: asus-wmi: Call led hw_changed API on
 kbd brightness change

On Thu, Jun 14, 2018 at 2:58 PM, Chris Chiu <chiu@...lessm.com> wrote:
> On Wed, Jun 13, 2018 at 8:49 PM, Andy Shevchenko
> <andy.shevchenko@...il.com> wrote:
>> On Mon, Jun 11, 2018 at 10:18 AM, Chris Chiu <chiu@...lessm.com> wrote:
>>> Make asus-wmi notify on hotkey kbd brightness changes, listen for
>>> brightness events and update the brightness directly in the driver.
>>
>>> For this purpose, bound check on brightness in kbd_led_set must be
>>> based on the same data type to prevent illegal value been set.
>>
>>> @@ -497,9 +498,9 @@ static void kbd_led_set(struct led_classdev *led_cdev,
>>>
>>>         asus = container_of(led_cdev, struct asus_wmi, kbd_led);
>>>
>>> -       if (value > asus->kbd_led.max_brightness)
>>> +       if ((int)value > (int)asus->kbd_led.max_brightness)
>>>                 value = asus->kbd_led.max_brightness;
>>> -       else if (value < 0)
>>> +       else if ((int)value < 0)
>>>                 value = 0;
>>
>> I didn't quite understand this part of the problem.
>> Does it exist in the current code? Can it be split to a separate change?
>>
>> Can we avoid those ugly castings?
>>
>
> I'd like to remove the ugly castings but there's a concern I may need some
> advices. I don't know whether if the bound check logic ever verified before.
> Maybe the value passed via sysfs is already correctly bounded?
>
> When the kbd_led_wk comes to -1, `if (value > asus->kbd_led.max_brightness)`
> returns true and `if (value < 0)` return false which confused me. It
> should relate
> to the 2nd argument type is enum led_brightness which I consider it as integer.
> The unexpected return value cause the KBD_BRTDWN cyclic, 3->2->0->-1
> (3 again in kbd_led_set)->2->1. After applying the casting on both operands
> `if ((int)value > (int)asus->kbd_led.max_brightness)`, the other
> unexpected false
> returned by `if (value < 0)` makes each KBD_BRTDOWN to be 3 -> 2 -> 1 -> 0 ->
> -1 -> -2 -> -3 ->..... That's what the ugly casting for. I used to
> tend to do boundary
> limit before calling kbd_led_set as follows
>
> kbd_led_set(&asus->kbd_led, MIN(asus->kbd_led_wk + 1,
> asus->kbd_led.max_brightness);
> and
> kbd_led_set(&asus->kbd_led, MAX(asus->kbd_led_wk - 1, 0));
>
> If so, the boundary limit logic would be totally redundant but I think
> it may be still
> useful to check the value passed from sysfs? Any suggestion which one would
> be better?
>
> Chris
>
>> --
>> With Best Regards,
>> Andy Shevchenko

Gentle ping.

Cheers.

Chris