2015-03-27 9:36 GMT+01:00 Daniel Lezcano [off-list ref]:

On 03/26/2015 09:19 PM, Maxime Coquelin wrote:

quoted

Hi Daniel,

   Thanks for the review. Please find my answers below.

2015-03-26 10:50 GMT+01:00 Daniel Lezcano [off-list ref]:

quoted

On 03/12/2015 10:55 PM, Maxime Coquelin wrote:

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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

[ ... ]

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+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;

}

Ok, it looks sensible.
I will do this in next version.

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+       }
+
+       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.

quoted

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 ...).

Ok, let's keep the error path, that's much cleaner indeed.

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

pr_warn

Sure, will fix.

Thanks,
Maxime

Thanks

  -- Daniel


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