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Date: Thu, 26 Mar 2015 21:19:58 +0100
From: Maxime Coquelin <mcoquelin.stm32@...il.com>
To: Daniel Lezcano <daniel.lezcano@...aro.org>
Cc: Uwe Kleine-König
<u.kleine-koenig@...gutronix.de>,
Andreas Färber <afaerber@...e.de>,
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Subject: Re: [PATCH v3 04/15] clocksource: Add ARM System timer driver
Hi Daniel,
Thanks for the review. Please find my answers below.
2015-03-26 10:50 GMT+01:00 Daniel Lezcano <daniel.lezcano@...aro.org>:
> On 03/12/2015 10:55 PM, Maxime Coquelin wrote:
>>
>> From: Maxime Coquelin <mcoquelin.stm32@...il.com>
>>
>> This patch adds clocksource support for ARMv7-M's System timer,
>> also known as SysTick.
>>
>> Signed-off-by: Maxime Coquelin <mcoquelin.stm32@...il.com>
>
>
> Hi Maxime,
>
> the driver looks good. Three comments below.
>
> -- Daniel
>
>
>> ---
>> drivers/clocksource/Kconfig | 7 ++++
>> drivers/clocksource/Makefile | 1 +
>> drivers/clocksource/armv7m_systick.c | 78
>> ++++++++++++++++++++++++++++++++++++
>> 3 files changed, 86 insertions(+)
>> create mode 100644 drivers/clocksource/armv7m_systick.c
>>
>> diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
>> index 1c2506f..b82e58b 100644
>> --- a/drivers/clocksource/Kconfig
>> +++ b/drivers/clocksource/Kconfig
>> @@ -134,6 +134,13 @@ config CLKSRC_ARM_GLOBAL_TIMER_SCHED_CLOCK
>> help
>> Use ARM global timer clock source as sched_clock
>>
>> +config ARMV7M_SYSTICK
>> + bool
>> + select CLKSRC_OF if OF
>> + select CLKSRC_MMIO
>> + help
>> + This options enables support for the ARMv7M system timer unit
>> +
>> config ATMEL_PIT
>> select CLKSRC_OF if OF
>> def_bool SOC_AT91SAM9 || SOC_SAMA5
>> diff --git a/drivers/clocksource/Makefile b/drivers/clocksource/Makefile
>> index 752d5c7..1c9a643 100644
>> --- a/drivers/clocksource/Makefile
>> +++ b/drivers/clocksource/Makefile
>> @@ -44,6 +44,7 @@ obj-$(CONFIG_MTK_TIMER) += mtk_timer.o
>>
>> obj-$(CONFIG_ARM_ARCH_TIMER) += arm_arch_timer.o
>> obj-$(CONFIG_ARM_GLOBAL_TIMER) += arm_global_timer.o
>> +obj-$(CONFIG_ARMV7M_SYSTICK) += armv7m_systick.o
>> obj-$(CONFIG_CLKSRC_METAG_GENERIC) += metag_generic.o
>> obj-$(CONFIG_ARCH_HAS_TICK_BROADCAST) += dummy_timer.o
>> obj-$(CONFIG_ARCH_KEYSTONE) += timer-keystone.o
>> diff --git a/drivers/clocksource/armv7m_systick.c
>> b/drivers/clocksource/armv7m_systick.c
>> new file mode 100644
>> index 0000000..23d8249
>> --- /dev/null
>> +++ b/drivers/clocksource/armv7m_systick.c
>> @@ -0,0 +1,78 @@
>> +/*
>> + * Copyright (C) Maxime Coquelin 2015
>> + * Author: Maxime Coquelin <mcoquelin.stm32@...il.com>
>> + * License terms: GNU General Public License (GPL), version 2
>> + */
>> +
>> +#include <linux/kernel.h>
>> +#include <linux/clocksource.h>
>> +#include <linux/clockchips.h>
>> +#include <linux/of.h>
>> +#include <linux/of_address.h>
>> +#include <linux/clk.h>
>> +#include <linux/bitops.h>
>> +
>> +#define SYST_CSR 0x00
>> +#define SYST_RVR 0x04
>> +#define SYST_CVR 0x08
>> +#define SYST_CALIB 0x0c
>> +
>> +#define SYST_CSR_ENABLE BIT(0)
>> +
>> +#define SYSTICK_LOAD_RELOAD_MASK 0x00FFFFFF
>> +
>> +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?
>
>> + }
>> +
>> + 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?
Regards,
Maxime
>
>> + clk_disable_unprepare(clk);
>> +out_unmap:
>> + iounmap(base);
>> + WARN(ret, "ARM System timer register failed (%d)\n", ret);
>> +}
>> +
>> +CLOCKSOURCE_OF_DECLARE(arm_systick, "arm,armv7m-systick",
>> + system_timer_of_register);
>>
>
>
> --
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>
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