linux-kernel - Re: [PATCH v2 2/5] media: venus: add a routine to set venus state

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Date:   Mon, 4 Jun 2018 21:54:25 +0900
From:   Tomasz Figa <tfiga@...omium.org>
To:     vgarodia@...eaurora.org, Hans Verkuil <hverkuil@...all.nl>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Rob Herring <robh@...nel.org>,
        Mark Rutland <mark.rutland@....com>, andy.gross@...aro.org,
        bjorn.andersson@...aro.org,
        Stanimir Varbanov <stanimir.varbanov@...aro.org>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        linux-soc@...r.kernel.org, devicetree@...r.kernel.org,
        Alexandre Courbot <acourbot@...omium.org>
Subject: Re: [PATCH v2 2/5] media: venus: add a routine to set venus state

Hi Jordan, Vikash,

On Sat, Jun 2, 2018 at 6:21 AM Jordan Crouse <jcrouse@...eaurora.org> wrote:
>
> On Sat, Jun 02, 2018 at 01:56:05AM +0530, Vikash Garodia wrote:
[snip]
> > +int venus_set_hw_state(enum tzbsp_video_state state, struct venus_core *core)
> > +{
> > +     int ret;
> > +     struct device *dev = core->dev;
>
> If you get rid of the log message as you should, you don't need this.
>
> > +     void __iomem *reg_base = core->base;
> > +
> > +     switch (state) {
> > +     case TZBSP_VIDEO_SUSPEND:
> > +             if (qcom_scm_is_available())
> > +                     ret = qcom_scm_set_remote_state(TZBSP_VIDEO_SUSPEND, 0);
> > +             else
> > +                     writel_relaxed(1, reg_base + WRAPPER_A9SS_SW_RESET);
>
> You can just use core->base here and not bother making a local variable for it.
>
> > +             break;
> > +     case TZBSP_VIDEO_RESUME:
> > +             if (qcom_scm_is_available())
> > +                     ret = qcom_scm_set_remote_state(TZBSP_VIDEO_RESUME, 0);
> > +             else
> > +                     venus_reset_hw(core);
> > +             break;
> > +     default:
> > +             dev_err(dev, "invalid state\n");
>
> state is a enum - you are highly unlikely to be calling it in your own code with
> a random value.  It is smart to have the default, but you don't need the log
> message - that is just wasted space in the binary.
>
> > +             break;
> > +     }
>
> There are three paths in the switch statement that could end up with 'ret' being
> uninitialized here.  Set it to 0 when you declare it.

Does this actually compile? The compiler should detect that ret is
used uninitialized. Setting it to 0 at declaration time actually
prevents compiler from doing that and makes it impossible to catch
cases when the ret should actually be non-zero, e.g. the invalid enum
value case.

Given that this function is supposed to substitute existing calls into
qcom_scm_set_remote_state(), why not just do something like this:

        if (qcom_scm_is_available())
                return qcom_scm_set_remote_state(state, 0);

        switch (state) {
        case TZBSP_VIDEO_SUSPEND:
                writel_relaxed(1, reg_base + WRAPPER_A9SS_SW_RESET);
                break;
        case TZBSP_VIDEO_RESUME:
                venus_reset_hw(core);
                break;
        }

        return 0;

Best regards,
Tomasz