Re: [PATCH v3 04/15] clocksource: Add ARM System timer driver

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



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

From: Maxime Coquelin <mcoquelin.stm32@xxxxxxxxx>

This patch adds clocksource support for ARMv7-M's System timer,
also known as SysTick.

Signed-off-by: Maxime Coquelin <mcoquelin.stm32@xxxxxxxxx>


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

--
 <http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs

Follow Linaro:  <http://www.facebook.com/pages/Linaro> Facebook |
<http://twitter.com/#!/linaroorg> Twitter |
<http://www.linaro.org/linaro-blog/> Blog

--
To unsubscribe from this list: send the line "unsubscribe linux-gpio" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html




[Index of Archives]     [Linux SPI]     [Linux Kernel]     [Linux ARM (vger)]     [Linux ARM MSM]     [Linux Omap]     [Linux Arm]     [Linux Tegra]     [Fedora ARM]     [Linux for Samsung SOC]     [eCos]     [Linux Fastboot]     [Gcc Help]     [Git]     [DCCP]     [IETF Announce]     [Security]     [Linux MIPS]     [Yosemite Campsites]

  Powered by Linux