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
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