From: Daniel Lezcano <daniel.lezcano@linaro.org>
To: Maxime Coquelin <mcoquelin.stm32@gmail.com>
Cc: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>,
"Andreas Färber" <afaerber@suse.de>,
"Geert Uytterhoeven" <geert@linux-m68k.org>,
"Rob Herring" <robh+dt@kernel.org>,
"Philipp Zabel" <p.zabel@pengutronix.de>,
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"Arnd Bergmann" <arnd@arndb.de>, "Stefan Agner" <stefan@agner.ch>,
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"Paul Bolle" <pebolle@tiscali.nl>,
"Jonathan Corbet" <corbet@lwn.net>,
"Pawel Moll" <pawel.moll@arm.com>,
"Mark Rutland" <mark.rutland@arm.com>,
"Ian Campbell" <ijc+devicetree@hellion.org.uk>,
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Subject: Re: [PATCH v3 04/15] clocksource: Add ARM System timer driver
Date: Fri, 27 Mar 2015 09:36:37 +0100 [thread overview]
Message-ID: <55151695.5050203@linaro.org> (raw)
In-Reply-To: <CALszF6CtEf0w8AoaMwFzn34ACMjkW6obT5_MrduBdUOm7T=zNw@mail.gmail.com>
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
--
<http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs
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next prev parent reply other threads:[~2015-03-27 8:36 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-03-12 21:55 [PATCH v3 00/15] Add support to STMicroelectronics STM32 family Maxime Coquelin
2015-03-12 21:55 ` [PATCH v3 01/15] scripts: link-vmlinux: Don't pass page offset to kallsyms if XIP Kernel Maxime Coquelin
2015-03-12 21:55 ` [PATCH v3 02/15] ARM: ARMv7-M: Enlarge vector table up to 256 entries Maxime Coquelin
2015-03-12 21:55 ` [PATCH v3 03/15] dt-bindings: Document the ARM System timer bindings Maxime Coquelin
2015-03-12 21:55 ` [PATCH v3 04/15] clocksource: Add ARM System timer driver Maxime Coquelin
2015-03-26 9:50 ` Daniel Lezcano
2015-03-26 20:19 ` Maxime Coquelin
2015-03-27 8:36 ` Daniel Lezcano [this message]
2015-03-27 12:33 ` Maxime Coquelin
2015-03-12 21:55 ` [PATCH v3 05/15] dt-bindings: Document the STM32 reset bindings Maxime Coquelin
2015-03-13 0:09 ` Chanwoo Choi
2015-03-17 16:57 ` Maxime Coquelin
2015-03-13 8:50 ` Philipp Zabel
2015-03-17 17:13 ` Maxime Coquelin
2015-03-12 21:55 ` [PATCH v3 06/15] drivers: reset: Add STM32 reset driver Maxime Coquelin
2015-03-13 0:11 ` Chanwoo Choi
2015-03-13 8:54 ` Philipp Zabel
2015-03-17 17:23 ` Maxime Coquelin
2015-03-12 21:55 ` [PATCH v3 07/15] dt-bindings: Document the STM32 timer bindings Maxime Coquelin
2015-03-12 21:55 ` [PATCH v3 08/15] clockevent: Add STM32 Timer driver Maxime Coquelin
2015-03-12 21:55 ` [PATCH v3 09/15] dt-bindings: Document the STM32 USART bindings Maxime Coquelin
2015-03-12 21:55 ` [PATCH v3 10/15] serial: stm32-usart: Add STM32 USART Driver Maxime Coquelin
2015-03-13 9:41 ` Paul Bolle
2015-03-17 17:39 ` Maxime Coquelin
2015-03-13 14:19 ` Andy Shevchenko
2015-03-17 17:32 ` Maxime Coquelin
2015-03-17 17:56 ` Andy Shevchenko
2015-03-19 13:55 ` Maxime Coquelin
2015-03-19 14:58 ` Peter Hurley
2015-03-19 17:35 ` Maxime Coquelin
2015-03-24 17:21 ` Maxime Coquelin
2015-03-24 17:44 ` Peter Hurley
2015-03-24 18:23 ` Peter Hurley
2015-03-26 15:46 ` Russell King - ARM Linux
2015-03-26 22:05 ` Maxime Coquelin
2015-03-26 22:03 ` Maxime Coquelin
2015-03-27 11:32 ` Peter Hurley
2015-03-27 12:30 ` Maxime Coquelin
2015-03-12 21:55 ` [PATCH v3 11/15] ARM: Add STM32 family machine Maxime Coquelin
2015-03-12 21:55 ` [PATCH v3 12/15] ARM: dts: Add ARM System timer as clockevent in armv7m Maxime Coquelin
2015-03-12 21:55 ` [PATCH v3 13/15] ARM: dts: Introduce STM32F429 MCU Maxime Coquelin
2015-03-12 21:56 ` [PATCH v3 14/15] ARM: configs: Add STM32 defconfig Maxime Coquelin
2015-03-12 21:56 ` [PATCH v3 15/15] MAINTAINERS: Add entry for STM32 MCUs Maxime Coquelin
2015-03-12 23:45 ` [PATCH v3 00/15] Add support to STMicroelectronics STM32 family Chanwoo Choi
2015-03-18 23:35 ` Chanwoo Choi
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