Subject: Re: [PATCH V2 2/6] clocksource: tegra: add Tegra210 timer driver

From: Thierry Reding <[email-masked]>
Date: Mon, 28 Jan 2019 16:09:08 +0100

On Mon, Jan 28, 2019 at 05:18:11PM +0800, Joseph Lo wrote:
> Add support for the Tegra210 timer that runs at oscillator clock
> (TMR10-TMR13). We need these timers to work as clock event device and to
> replace the ARMv8 architected timer due to it can't survive across the
> power cycle of the CPU core or CPUPORESET signal. So it can't be a wake-up
> source when CPU suspends in power down state.
> 
> Based on the work of Antti P Miettinen <[email-masked]>
> 
> Cc: Daniel Lezcano <[email-masked]>
> Cc: Thomas Gleixner <[email-masked]>
> Cc: [email-masked]
> Signed-off-by: Joseph Lo <[email-masked]>
> ---
> v2:
>  * add error clean-up code
> ---
>  drivers/clocksource/Kconfig          |   3 +
>  drivers/clocksource/Makefile         |   1 +
>  drivers/clocksource/timer-tegra210.c | 268 +++++++++++++++++++++++++++
>  include/linux/cpuhotplug.h           |   1 +
>  4 files changed, 273 insertions(+)
>  create mode 100644 drivers/clocksource/timer-tegra210.c
> 
> diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
> index a9e26f6a81a1..e6e3e64b6320 100644
> --- a/drivers/clocksource/Kconfig
> +++ b/drivers/clocksource/Kconfig
> @@ -135,6 +135,9 @@ config TEGRA_TIMER
>  	help
>  	  Enables support for the Tegra driver.
>  
> +config TEGRA210_TIMER
> +	def_bool ARCH_TEGRA_210_SOC
> +
>  config VT8500_TIMER
>  	bool "VT8500 timer driver" if COMPILE_TEST
>  	depends on HAS_IOMEM
> diff --git a/drivers/clocksource/Makefile b/drivers/clocksource/Makefile
> index cdd210ff89ea..95de59c8a47b 100644
> --- a/drivers/clocksource/Makefile
> +++ b/drivers/clocksource/Makefile
> @@ -36,6 +36,7 @@ obj-$(CONFIG_SUN4I_TIMER)	+= timer-sun4i.o
>  obj-$(CONFIG_SUN5I_HSTIMER)	+= timer-sun5i.o
>  obj-$(CONFIG_MESON6_TIMER)	+= timer-meson6.o
>  obj-$(CONFIG_TEGRA_TIMER)	+= timer-tegra20.o
> +obj-$(CONFIG_TEGRA210_TIMER)	+= timer-tegra210.o
>  obj-$(CONFIG_VT8500_TIMER)	+= timer-vt8500.o
>  obj-$(CONFIG_NSPIRE_TIMER)	+= timer-zevio.o
>  obj-$(CONFIG_BCM_KONA_TIMER)	+= bcm_kona_timer.o
> diff --git a/drivers/clocksource/timer-tegra210.c b/drivers/clocksource/timer-tegra210.c
> new file mode 100644
> index 000000000000..477b164e540b
> --- /dev/null
> +++ b/drivers/clocksource/timer-tegra210.c
> @@ -0,0 +1,268 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (c) 2014-2019, NVIDIA CORPORATION.  All rights reserved.
> + */
> +
> +#include <linux/clk.h>
> +#include <linux/clockchips.h>
> +#include <linux/cpu.h>
> +#include <linux/cpumask.h>
> +#include <linux/err.h>
> +#include <linux/interrupt.h>
> +#include <linux/io.h>
> +#include <linux/of_address.h>
> +#include <linux/of_irq.h>
> +#include <linux/percpu.h>
> +#include <linux/syscore_ops.h>
> +
> +static u32 tegra210_timer_freq;
> +static void __iomem *tegra210_timer_reg_base;
> +static u32 usec_config;
> +
> +#define TIMER_PTV		0x0
> +#define TIMER_PTV_EN		BIT(31)
> +#define TIMER_PTV_PER		BIT(30)
> +#define TIMER_PCR		0x4
> +#define TIMER_PCR_INTR_CLR	BIT(30)
> +#define TIMERUS_CNTR_1US	0x10
> +#define TIMERUS_USEC_CFG	0x14
> +
> +#define TIMER10_OFFSET		0x90
> +#define TIMER10_IRQ_IDX		10
> +
> +#define TIMER_FOR_CPU(cpu) (TIMER10_OFFSET + (cpu) * 8)
> +#define IRQ_IDX_FOR_CPU(cpu)	(TIMER10_IRQ_IDX + cpu)
> +
> +struct tegra210_clockevent {
> +	struct clock_event_device evt;
> +	char name[20];
> +	void __iomem *reg_base;
> +};
> +#define to_tegra_cevt(p) (container_of(p, struct tegra210_clockevent, evt))
> +
> +static struct tegra210_clockevent __percpu *tegra210_evt;
> +
> +static int tegra210_timer_set_next_event(unsigned long cycles,
> +					 struct clock_event_device *evt)
> +{
> +	struct tegra210_clockevent *tevt;
> +
> +	tevt = to_tegra_cevt(evt);
> +	writel(TIMER_PTV_EN |
> +	       ((cycles > 1) ? (cycles - 1) : 0), /* n+1 scheme */
> +	       tevt->reg_base + TIMER_PTV);
> +
> +	return 0;
> +}
> +
> +static inline void timer_shutdown(struct tegra210_clockevent *tevt)
> +{
> +	writel(0, tevt->reg_base + TIMER_PTV);
> +}
> +
> +static int tegra210_timer_shutdown(struct clock_event_device *evt)
> +{
> +	struct tegra210_clockevent *tevt;
> +
> +	tevt = to_tegra_cevt(evt);
> +	timer_shutdown(tevt);
> +
> +	return 0;
> +}
> +
> +static int tegra210_timer_set_periodic(struct clock_event_device *evt)
> +{
> +	struct tegra210_clockevent *tevt;
> +
> +	tevt = to_tegra_cevt(evt);
> +	writel(TIMER_PTV_EN | TIMER_PTV_PER | ((tegra210_timer_freq / HZ) - 1),
> +	       tevt->reg_base + TIMER_PTV);
> +
> +	return 0;
> +}
> +
> +static irqreturn_t tegra210_timer_isr(int irq, void *dev_id)
> +{
> +	struct tegra210_clockevent *tevt;
> +
> +	tevt = dev_id;
> +	writel(TIMER_PCR_INTR_CLR, tevt->reg_base + TIMER_PCR);
> +	tevt->evt.event_handler(&tevt->evt);
> +
> +	return IRQ_HANDLED;
> +}

Up to here this is a duplicate of timer-tegra20.c. And a lot of
tegra210_timer_init() is the same as tegra20_timer_init() as well. Can't
we unify the two drivers instead?

The power cycle restrictions of the architected timer, do they not apply
to chips earlier than Tegra210 either? So don't we need all of these
additional features on the timer-tegra20.c driver as well? If so that
would increase the code duplication even more. I think we should avoid
that, unless there are any strong arguments that would justify it.

Thierry
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