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Date:   Mon, 15 Apr 2019 14:36:39 +0200
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Bartosz Golaszewski <brgl@...ev.pl>, Sekhar Nori <nsekhar@...com>,
        Kevin Hilman <khilman@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        David Lechner <david@...hnology.com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Bartosz Golaszewski <bgolaszewski@...libre.com>
Subject: Re: [PATCH v4 01/11] clocksource: davinci-timer: new driver

On 18/03/2019 13:10, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <bgolaszewski@...libre.com>
> 
> Currently the clocksource and clockevent support for davinci platforms
> lives in mach-davinci. It hard-codes many things, uses global variables,
> implements functionalities unused by any platform and has code fragments
> scattered across many (often unrelated) files.
> 
> Implement a new, modern and simplified timer driver and put it into
> drivers/clocksource. We still need to support legacy board files so
> export a config structure and a function that allows machine code to
> register the timer.
> 
> We don't bother freeing resources on errors in davinci_timer_register()
> as the system won't boot without a timer anyway.

Can you give a quick description of the timer hardware and how it works?

> Signed-off-by: Bartosz Golaszewski <bgolaszewski@...libre.com>
> Reviewed-by: David Lechner <david@...hnology.com>
> ---
>  drivers/clocksource/Kconfig         |   5 +
>  drivers/clocksource/Makefile        |   1 +
>  drivers/clocksource/timer-davinci.c | 438 ++++++++++++++++++++++++++++
>  include/clocksource/timer-davinci.h |  44 +++
>  4 files changed, 488 insertions(+)
>  create mode 100644 drivers/clocksource/timer-davinci.c
>  create mode 100644 include/clocksource/timer-davinci.h
> 
> diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
> index 171502a356aa..08b1f539cfc4 100644
> --- a/drivers/clocksource/Kconfig
> +++ b/drivers/clocksource/Kconfig
> @@ -42,6 +42,11 @@ config BCM_KONA_TIMER
>  	help
>  	  Enables the support for the BCM Kona mobile timer driver.
>  
> +config DAVINCI_TIMER
> +	bool "Texas Instruments DaVinci timer driver"

Make the option silent (eg. if COMPILE_TEST)

> +	help
> +	  Enables the support for the TI DaVinci timer driver.
> +
>  config DIGICOLOR_TIMER
>  	bool "Digicolor timer driver" if COMPILE_TEST
>  	select CLKSRC_MMIO
> diff --git a/drivers/clocksource/Makefile b/drivers/clocksource/Makefile
> index be6e0fbc7489..3c73d0e58b45 100644
> --- a/drivers/clocksource/Makefile
> +++ b/drivers/clocksource/Makefile
> @@ -15,6 +15,7 @@ obj-$(CONFIG_SH_TIMER_TMU)	+= sh_tmu.o
>  obj-$(CONFIG_EM_TIMER_STI)	+= em_sti.o
>  obj-$(CONFIG_CLKBLD_I8253)	+= i8253.o
>  obj-$(CONFIG_CLKSRC_MMIO)	+= mmio.o
> +obj-$(CONFIG_DAVINCI_TIMER)	+= timer-davinci.o
>  obj-$(CONFIG_DIGICOLOR_TIMER)	+= timer-digicolor.o
>  obj-$(CONFIG_OMAP_DM_TIMER)	+= timer-ti-dm.o
>  obj-$(CONFIG_DW_APB_TIMER)	+= dw_apb_timer.o
> diff --git a/drivers/clocksource/timer-davinci.c b/drivers/clocksource/timer-davinci.c
> new file mode 100644
> index 000000000000..46dfc4d457fc
> --- /dev/null
> +++ b/drivers/clocksource/timer-davinci.c
> @@ -0,0 +1,438 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +//
> +// TI DaVinci clocksource driver
> +//
> +// Copyright (C) 2019 Texas Instruments
> +// Author: Bartosz Golaszewski <bgolaszewski@...libre.com>
> +// (with some parts adopted from code by Kevin Hilman <khilman@...libre.com>)
> +
> +#include <linux/clk.h>
> +#include <linux/clockchips.h>
> +#include <linux/clocksource.h>
> +#include <linux/err.h>
> +#include <linux/interrupt.h>
> +#include <linux/kernel.h>
> +#include <linux/of_address.h>
> +#include <linux/of_irq.h>
> +#include <linux/sched_clock.h>
> +
> +#include <clocksource/timer-davinci.h>
> +
> +#undef pr_fmt
> +#define pr_fmt(fmt) "%s: " fmt "\n", __func__
> +
> +#define DAVINCI_TIMER_REG_TIM12			0x10
> +#define DAVINCI_TIMER_REG_TIM34			0x14
> +#define DAVINCI_TIMER_REG_PRD12			0x18
> +#define DAVINCI_TIMER_REG_PRD34			0x1c
> +#define DAVINCI_TIMER_REG_TCR			0x20
> +#define DAVINCI_TIMER_REG_TGCR			0x24
> +
> +#define DAVINCI_TIMER_TIMMODE_MASK		GENMASK(3, 2)
> +#define DAVINCI_TIMER_RESET_MASK		GENMASK(1, 0)
> +#define DAVINCI_TIMER_TIMMODE_32BIT_UNCHAINED	BIT(2)
> +#define DAVINCI_TIMER_UNRESET			GENMASK(1, 0)
> +
> +/* Shift depends on timer. */
> +#define DAVINCI_TIMER_ENAMODE_MASK		GENMASK(1, 0)
> +#define DAVINCI_TIMER_ENAMODE_DISABLED		0x00
> +#define DAVINCI_TIMER_ENAMODE_ONESHOT		BIT(0)
> +#define DAVINCI_TIMER_ENAMODE_PERIODIC		BIT(1)
> +
> +#define DAVINCI_TIMER_ENAMODE_SHIFT_TIM12	6
> +#define DAVINCI_TIMER_ENAMODE_SHIFT_TIM34	22
> +
> +#define DAVINCI_TIMER_MIN_DELTA			0x01
> +#define DAVINCI_TIMER_MAX_DELTA			0xfffffffe
> +
> +#define DAVINCI_TIMER_CLKSRC_BITS		32
> +
> +#define DAVINCI_TIMER_TGCR_DEFAULT \
> +		(DAVINCI_TIMER_TIMMODE_32BIT_UNCHAINED | DAVINCI_TIMER_UNRESET)
> +
> +enum {
> +	DAVINCI_TIMER_MODE_DISABLED = 0,
> +	DAVINCI_TIMER_MODE_ONESHOT,
> +	DAVINCI_TIMER_MODE_PERIODIC,
> +};

This is replicating what is already available. Right after set_periodic
or set_oneshot are called, the timer state is changed to respectively
CLOCK_EVT_STATE_PERIODIC and CLOCK_EVT_STATE_ONESHOT. So it is useless
to define those enum again as what you want is to check the timer mode.


[ ... ]

> +
> +	clocksource = kzalloc(sizeof(*clocksource), GFP_KERNEL);
> +	if (!clocksource) {
> +		pr_err("Error allocating memory for clocksource data");
> +		return -ENOMEM;
> +	}
> +
> +	clocksource->dev.rating = 300;
> +	clocksource->dev.read = davinci_timer_clksrc_read;
> +	clocksource->dev.mask = CLOCKSOURCE_MASK(DAVINCI_TIMER_CLKSRC_BITS);
> +	clocksource->dev.flags = CLOCK_SOURCE_IS_CONTINUOUS;

>>>

> +	clocksource->timer.set_period = davinci_timer_set_period_std;
> +	clocksource->timer.mode = DAVINCI_TIMER_MODE_PERIODIC;
> +	clocksource->timer.base = base;

What for?

<<<

> +	if (timer_cfg->cmp_off) {
> +		clocksource->timer.regs = &davinci_timer_tim12_regs;
> +		clocksource->dev.name = "tim12";
> +	} else {
> +		clocksource->timer.regs = &davinci_timer_tim34_regs;
> +		clocksource->dev.name = "tim34";
> +	}
> +
> +	rv = request_irq(timer_cfg->irq[DAVINCI_TIMER_CLOCKSOURCE_IRQ].start,
> +			 davinci_timer_irq_freerun, IRQF_TIMER,
> +			 "free-run counter", clocksource);
> +	if (rv) {
> +		pr_err("Unable to request the clocksource interrupt");
> +		return rv;
> +	}

Why do you have to request an interrupt to do nothing? Isn't possible to
let the timer run and wrap without generating interrupts?

[ ... ]




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