linux-kernel - Re: [PATCH] media: camss: csiphy-3ph: avoid undefined behavior

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Date:   Fri, 16 Dec 2022 11:59:34 +0100
From:   Robert Foss <robert.foss@...aro.org>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     Todor Tomov <todor.too@...il.com>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Arnd Bergmann <arnd@...db.de>, Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        Jonathan Marek <jonathan@...ek.ca>,
        "Bryan O'Donoghue" <bryan.odonoghue@...aro.org>,
        linux-media@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: camss: csiphy-3ph: avoid undefined behavior

On Thu, 15 Dec 2022 at 17:29, Arnd Bergmann <arnd@...nel.org> wrote:
>
> From: Arnd Bergmann <arnd@...db.de>
>
> Marking a case of the switch statement as unreachable means the
> compiler treats it as undefined behavior, which is then caught by
> an objtool warning:
>
> drivers/media/platform/qcom/camss/camss-csiphy-3ph-1-0.o: warning: objtool: csiphy_lanes_enable() falls through to next function csiphy_lanes_disable()
>
> Instead of simply continuing execution at a random place of the
> driver, print a warning and return from to the caller, which
> makes it possible to understand what happens and avoids the
> warning.
>
> Fixes: 53655d2a0ff2 ("media: camss: csiphy-3ph: add support for SM8250 CSI DPHY")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  drivers/media/platform/qcom/camss/camss-csiphy-3ph-1-0.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/media/platform/qcom/camss/camss-csiphy-3ph-1-0.c b/drivers/media/platform/qcom/camss/camss-csiphy-3ph-1-0.c
> index 451a4c9b3d30..04baa80494c6 100644
> --- a/drivers/media/platform/qcom/camss/camss-csiphy-3ph-1-0.c
> +++ b/drivers/media/platform/qcom/camss/camss-csiphy-3ph-1-0.c
> @@ -429,7 +429,8 @@ static void csiphy_gen2_config_lanes(struct csiphy_device *csiphy,
>                 array_size = ARRAY_SIZE(lane_regs_sm8250[0]);
>                 break;
>         default:
> -               unreachable();
> +               WARN(1, "unknown cspi version\n");
> +               return;
>         }
>
>         for (l = 0; l < 5; l++) {
> --
> 2.35.1
>

Reviewed-by: Robert Foss <robert.foss@...aro.org>