linux-kernel - Re: [PATCH 2/2] HID: i2c-hid: support the regulator

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Date:   Wed, 14 Sep 2016 16:02:42 +0800
From:   Brian Norris <briannorris@...omium.org>
To:     Benjamin Tissoires <benjamin.tissoires@...hat.com>
Cc:     Caesar Wang <wxt@...k-chips.com>, Jiri Kosina <jikos@...nel.org>,
        linux-rockchip@...ts.infradead.org, dbasehore@...omium.org,
        Douglas Anderson <dianders@...omium.org>,
        Heiko Stuebner <heiko@...ech.de>, linux-input@...r.kernel.org,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Dmitry Torokhov <dtor@...omium.org>,
        Benson Leung <bleung@...omium.org>,
        Guohua Zhong <ghzhong@...angdigital.com>,
        "Zhonghui\"" <zhonghui.fu@...ux.intel.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] HID: i2c-hid: support the regulator

On Wed, Sep 14, 2016 at 03:55:05PM +0800, Brian Norris wrote:
> The default behavior of regulator_get() is to provide a dummy regulator
> if none is found. So the pointer is never NULL, and it won't break
> devices without a regulator. If you don't want a dummy regulator you
> would use regulator_get_optional() instead, and you would then need to
> handle ERR_PTR(-ENODEV) specifically.

One caveat to the never-NULL comment above that I just noticed:

If CONFIG_REGULATOR=n, then regulator_get() actually returns NULL (see
include/linux/regulator/consumer.h), but it also specifically has a
comment right next to that NULL return, saying:

        /* Nothing except the stubbed out regulator API should be
         * looking at the value except to check if it is an error
         * value. Drivers are free to handle NULL specifically by
         * skipping all regulator API calls, but they don't have to.
         * Drivers which don't, should make sure they properly handle
         * corner cases of the API, such as regulator_get_voltage()
         * returning 0.
         */

So, we still don't need to handle the NULL case specially.

Brian