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    SubjectRe: [PATCH v3 04/15] clocksource: Add ARM System timer driver
    On 03/26/2015 09:19 PM, Maxime Coquelin wrote:
    > Hi Daniel,
    >
    > Thanks for the review. Please find my answers below.
    >
    > 2015-03-26 10:50 GMT+01:00 Daniel Lezcano <daniel.lezcano@linaro.org>:
    >> On 03/12/2015 10:55 PM, Maxime Coquelin wrote:
    >>>
    >>> From: Maxime Coquelin <mcoquelin.stm32@gmail.com>
    >>>
    >>> This patch adds clocksource support for ARMv7-M's System timer,
    >>> also known as SysTick.
    >>>
    >>> Signed-off-by: Maxime Coquelin <mcoquelin.stm32@gmail.com>
    >>
    >>
    >> Hi Maxime,
    >>
    >> the driver looks good. Three comments below.
    >>
    >> -- Daniel
    >>
    >>

    [ ... ]

    >>> +static void __init system_timer_of_register(struct device_node *np)
    >>> +{
    >>> + struct clk *clk;
    >>> + void __iomem *base;
    >>> + u32 rate = 0;
    >>> + int ret;
    >>> +
    >>> + base = of_iomap(np, 0);
    >>> + if (!base) {
    >>> + pr_warn("system-timer: invalid base address\n");
    >>> + return;
    >>> + }
    >>> +
    >>> + clk = of_clk_get(np, 0);
    >>> + if (!IS_ERR(clk)) {
    >>> + ret = clk_prepare_enable(clk);
    >>> + if (ret) {
    >>> + clk_put(clk);
    >>> + goto out_unmap;
    >>> + }
    >>> +
    >>> + rate = clk_get_rate(clk);
    >>> + }
    >>> +
    >>> + /* If no clock found, try to get clock-frequency property */
    >>> + if (!rate) {
    >>> + ret = of_property_read_u32(np, "clock-frequency", &rate);
    >>> + if (ret)
    >>> + goto out_unmap;
    >>
    >>
    >> Shouldn't be 'goto out_clk_disable' ?
    >
    > No, because I assumed !rate means we failed to get the clock.
    > Actually, clk_get_rate could return 0, so relying on rate value is not safe.
    >
    > I propose to get clock-frequency property if IS_ERR(clk).
    >
    > Is it fine for you?

    Why not invert the conditions ? If the 'clock-frequency' is specified in
    the DT then it overrides the clk_get_rate(). So the resulting code will be:

    ret = of_property_read_u32(np, "clock-frequency", &rate);
    if (ret) {
    clk = of_clk_get(np, 0);
    if (IS_ERR(clk))
    goto out_unmap;

    ret = clk_prepare_enable(clk);
    if (ret)
    goto out_clk_put;

    rate = clk_get_rate(clk);
    if (!rate)
    goto out_clk_unprepare;
    }



    >>> + }
    >>> +
    >>> + writel_relaxed(SYSTICK_LOAD_RELOAD_MASK, base + SYST_RVR);
    >>> + writel_relaxed(SYST_CSR_ENABLE, base + SYST_CSR);
    >>> +
    >>> + ret = clocksource_mmio_init(base + SYST_CVR, "arm_system_timer",
    >>> rate,
    >>> + 200, 24, clocksource_mmio_readl_down);
    >>> + if (ret) {
    >>> + pr_err("failed to init clocksource (%d)\n", ret);
    >>> + goto out_clk_disable;
    >>> + }
    >>> +
    >>> + pr_info("ARM System timer initialized as clocksource\n");
    >>> +
    >>> + return;
    >>> +
    >>> +out_clk_disable:
    >>> + if (!IS_ERR(clk))
    >>
    >>
    >> Why do you need this check ?
    >
    > To handle the case were no clock was found, but a clk-frequency value
    > was provided.
    >
    >>
    >> It isn't missing a clk_put ?
    >
    > Right, thanks for spotting this.
    >
    > I wonder if it makes sense to implement the error path.
    > If we fail to initialize the clocksource, the system will be unusable.
    >
    > Maybe I should just perform a BUG_ON() in the error cases, as most of
    > the other clocksource drivers do.
    > What is your view?

    I prefer to not BUG_ON in the init functions because it already happen
    that drivers were bugging at init time and when a driver was reused on
    another platform with several timers available, the board was not able
    to boot because one timer was not used, hence not defined in the DT. I
    don't know if that could be the case for this platform but I prefer to
    keep thing going smoothly and return from init even if that lead to a
    kernel hang. Of course, the errors must be displayed (pr_warn, pr_err,
    pr_notice, etc ...).

    >>
    >>> + clk_disable_unprepare(clk);
    >>> +out_unmap:
    >>> + iounmap(base);
    >>> + WARN(ret, "ARM System timer register failed (%d)\n", ret);

    pr_warn

    Thanks

    -- Daniel

    --
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