linux-kernel - Re: [PATCH v6 2/3] drm: bridge: Add thc63lvd1024 LVDS decoder driver

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Date:   Tue, 27 Mar 2018 10:36:40 +0200
From:   Andrzej Hajda <a.hajda@...sung.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Vladimir Zapolskiy <vladimir_zapolskiy@...tor.com>,
        Jacopo Mondi <jacopo+renesas@...ndi.org>,
        Archit Taneja <architt@...eaurora.org>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        David Airlie <airlied@...ux.ie>,
        Simon Horman <horms@...ge.net.au>,
        Magnus Damm <magnus.damm@...il.com>,
        Niklas Söderlund <niklas.soderlund@...natech.se>,
        Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 2/3] drm: bridge: Add thc63lvd1024 LVDS decoder
 driver

On 27.03.2018 09:36, Geert Uytterhoeven wrote:
> Hi Andrzej,
>
> On Tue, Mar 27, 2018 at 9:28 AM, Andrzej Hajda <a.hajda@...sung.com> wrote:
>>>> --- /dev/null
>>>> +++ b/drivers/gpu/drm/bridge/thc63lvd1024.c
>>>> +static void thc63_enable(struct drm_bridge *bridge)
>>>> +{
>>>> +    struct thc63_dev *thc63 = to_thc63(bridge);
>>>> +    struct regulator *vcc;
>>>> +    int i;
>>> unsigned int i;
>> Why? You are introducing silly bug this way, see few lines below.
>>
>>>> +
>>>> +    for (i = 0; i < ARRAY_SIZE(thc63->vccs); i++) {
>>>> +            vcc = thc63->vccs[i];
>>>> +            if (!vcc)
>>>> +                    continue;
>>>> +
>>>> +            if (regulator_enable(vcc))
>>>> +                    goto error_vcc_enable;
>>>> +    }
>>>> +
>>>> +    if (thc63->pdwn)
>>>> +            gpiod_set_value(thc63->pdwn, 0);
>>>> +
>>>> +    if (thc63->oe)
>>>> +            gpiod_set_value(thc63->oe, 1);
>>>> +
>>>> +    return;
>>>> +
>>>> +error_vcc_enable:
>>>> +    dev_err(thc63->dev, "Failed to enable regulator %s\n",
>>>> +            thc63_reg_names[i]);
>>>> +
>>>> +    for (i = i - 1; i >= 0; i--) {
>> Here, the loop will not end if you define i unsigned.
> True.
>
>> I know one can change the loop, to make it working with unsigned. But
>> this clearly shows that using unsigned is more risky.
>> What are advantages of unsigned vs int in this case. Are there some
>> guidelines/discussions about it?
> Some people consider signed integers harmful, as they may be converted
> silently by the compiler to the "larger" unsigned type when needed.

Wow, it sounds crazy, shall we expect gigantic patchsets, converting all
occurrences of int to "unsigned int" ? :)
I know both types have their pros and cons and can behave unexpectedly
in corner cases, but I do not see why unsigned should be preferred over
signed in general, or in this particular case.
I guess there were somewhere discussion about it, could you point me to
it if possible, to avoid unnecessary noise in this thread.

Regards
Andrzej

>
> Gr{oetje,eeting}s,
>
>                         Geert
>