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

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Message-ID: <20160914143102.GK25951@mail.corp.redhat.com>
Date:   Wed, 14 Sep 2016 16:31:02 +0200
From:   Benjamin Tissoires <benjamin.tissoires@...hat.com>
To:     Brian Norris <briannorris@...omium.org>
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 Sep 14 2016 or thereabouts, Brian Norris wrote:
> 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.

Well, all the other regulator calls are either regulator_enable() or
regulator_disable(), which in this case (CONFIG_REGULATOR=n) are
returning 0.

So I think the whole patch is safe in its current form. Thanks for the
explanations.

Acked-by: Benjamin Tissoires <benjamin.tissoires@...hat.com>

Cheers,
Benjamin

> 
> Brian