Messages in this thread | | | Date | Fri, 27 Mar 2015 09:36:37 +0100 | From | Daniel Lezcano <> | Subject | Re: [PATCH v3 04/15] clocksource: Add ARM System timer driver |
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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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