linux-kernel - Re: [PATCH v8 10/15] cpufreq: Add Kryo CPU scaling driver

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Date:   Sat, 19 May 2018 12:54:41 +0100
From:   Russell King - ARM Linux <linux@...linux.org.uk>
To:     ilialin@...eaurora.org
Cc:     'Viresh Kumar' <viresh.kumar@...aro.org>, mark.rutland@....com,
        nm@...com, catalin.marinas@....com, mturquette@...libre.com,
        will.deacon@....com, tfinkel@...eaurora.org,
        linux-kernel@...r.kernel.org, david.brown@...aro.org,
        nicolas.dechesne@...aro.org, linux-clk@...r.kernel.org,
        robh@...nel.org, andy.gross@...aro.org, celster@...eaurora.org,
        devicetree@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, broonie@...nel.org,
        linux-soc@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        rnayak@...eaurora.org, sboyd@...nel.org, rjw@...ysocki.net,
        lgirdwood@...il.com, amit.kucheria@...aro.org
Subject: Re: [PATCH v8 10/15] cpufreq: Add Kryo CPU scaling driver

On Sat, May 19, 2018 at 02:09:24PM +0300, ilialin@...eaurora.org wrote:
> +static int __init qcom_cpufreq_kryo_driver_init(void)
> +{
> +       struct device *cpu_dev_silver, *cpu_dev_gold;
> +       struct opp_table *opp_silver, *opp_gold;
> +       enum _msm8996_version msm8996_version;
> +       struct nvmem_cell *speedbin_nvmem;
> +       struct platform_device *pdev;
> +       struct device_node *np;
> +       u8 *speedbin;
> +       u32 versions;
> +       size_t len;
> +       int ret;
> +
> +       cpu_dev_silver = get_cpu_device(SILVER_LEAD);
> +       if (IS_ERR_OR_NULL(cpu_dev_silver))
> +               return PTR_ERR(cpu_dev_silver);
> +
> +       cpu_dev_gold = get_cpu_device(SILVER_LEAD);
> +       if (IS_ERR_OR_NULL(cpu_dev_gold))
> +               return PTR_ERR(cpu_dev_gold);
> +
> +       msm8996_version = qcom_cpufreq_kryo_get_msm_id();
> +       if (NUM_OF_MSM8996_VERSIONS == msm8996_version) {
> +               dev_err(cpu_dev_silver, "Not Snapdragon 820/821!");
> +               return -ENODEV;
> +       }
> +
> +       np = dev_pm_opp_of_get_opp_desc_node(cpu_dev_silver);
> +       if (IS_ERR_OR_NULL(np))
> +               return PTR_ERR(np);

This function (qcom_cpufreq_kryo_driver_init) returns zero on success.
You are checking "np" here for being an error pointer, or NULL.
What value do you think PTR_ERR() returns in the case of PTR_ERR(NULL)?

IS_ERR_OR_NULL() is considered by some (me included) as being _very_
harmful because programmers generally fail to look at linux/err.h and
consider what it means when used as above.

-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
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