linux-kernel - Re: [PATCH v4 1/4] HID: add driver for Valve Steam Controller

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Date:   Thu, 1 Mar 2018 21:57:13 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Rodrigo Rivas Costa <rodrigorivascosta@...il.com>
Cc:     Jiri Kosina <jikos@...nel.org>,
        Benjamin Tissoires <benjamin.tissoires@...hat.com>,
        "Pierre-Loup A. Griffais" <pgriffais@...vesoftware.com>,
        Cameron Gutman <aicommander@...il.com>,
        Clément VUCHENER <clement.vuchener@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-input <linux-input@...r.kernel.org>
Subject: Re: [PATCH v4 1/4] HID: add driver for Valve Steam Controller

On Thu, Mar 1, 2018 at 9:13 PM, Rodrigo Rivas Costa
<rodrigorivascosta@...il.com> wrote:
> On Thu, Mar 01, 2018 at 12:20:37PM +0200, Andy Shevchenko wrote:
>> On Thu, Mar 1, 2018 at 12:49 AM, Rodrigo Rivas Costa
>> <rodrigorivascosta@...il.com> wrote:
>> > On Wed, Feb 28, 2018 at 09:21:15PM +0200, Andy Shevchenko wrote:
>> >> On Wed, Feb 28, 2018 at 8:43 PM, Rodrigo Rivas Costa
>> >> <rodrigorivascosta@...il.com> wrote:

> My bad, I didn't mean a literal free() call. More like:
>
> static void steam_unregister(struct steam_device *steam)
> {
>         struct input_dev *input;
>         struct power_supply *battery;
>
>         rcu_read_lock();
>         input = rcu_dereference(steam->input);
>         battery = rcu_dereference(steam->battery);
>         input_gyro = rcu_dereference(steam->input_gyro);
>         rcu_read_unlock();
>

>         if (input) {
>                 RCU_INIT_POINTER(steam->input, NULL);
>                 synchronize_rcu();
>                 hid_info(steam->hdev, "Steam Controller '%s' disconnected",
>                                 steam->serial_no);
>                 input_unregister_device(input);

Candidate for a helper

static void steam_unregister_input(...)
{
...
}


steam_unregister_input(input);

>         }

>         if (battery) {
>                 RCU_INIT_POINTER(steam->battery, NULL);
>                 synchronize_rcu();
>                 power_supply_unregister(battery);
>         }

Ditto.

>         if (input_gyro) {
>                 RCU_INIT_POINTER(steam->input_gyro, NULL);
>                 synchronize_rcu();
>                 input_unregister_device(input_gyro);
>         }

Ditto.

> }
>
> Also I think input_unregister_device() does not admit a NULL pointer.
> Having a special `if (!input_gyro)return;` at the end looks just
> wrong to me, it is no different from the other ones.

See above. Hide that detail in a helper function.

-- 
With Best Regards,
Andy Shevchenko