Re: [PATCH v4 01/11] clocksource: davinci-timer: new driver

From: Bartosz Golaszewski
Date: Tue Apr 16 2019 - 09:44:54 EST

pon., 15 kwi 2019 o 14:36 Daniel Lezcano <daniel.lezcano@xxxxxxxxxx> napisaÅ(a):
>
> On 18/03/2019 13:10, Bartosz Golaszewski wrote:
> > From: Bartosz Golaszewski <bgolaszewski@xxxxxxxxxxxx>
> >
> > 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?
>

Will do.

> > Signed-off-by: Bartosz Golaszewski <bgolaszewski@xxxxxxxxxxxx>
> > Reviewed-by: David Lechner <david@xxxxxxxxxxxxxx>
> > ---
> > 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)
>

Sure, I already did it locally after your last review.

> > + 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@xxxxxxxxxxxx>
> > +// (with some parts adopted from code by Kevin Hilman <khilman@xxxxxxxxxxxx>)
> > +
> > +#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.
>

I did it like this because I'm reusing the code in
davinci_timer_set_period_std() for both clocksource and clockevent
timers. If you prefer it be split to reuse the clockevent accessors, I
can do this (see below).

>
> [ ... ]
>
> > +
> > + 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?
>

What am I assigning the timer for? In order to call
davinci_timer_set_period() on it at the bottom of the init function.
I'm not sure if it is a problem you're pointing out, but as I said
above - I can configure the clocksource timer by hand in the init
function, drop the davinci_timer_clocksource structure and use the
clockevent accessors for checking the clock mode if you prefer it that
way. Would that be fine?

> <<<
>
> > + 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?
>

Yes it is, but the already existing DT bindings define two interrupts.
It's true that nobody uses it, but I thought I'd stick with what was
done before. If you prefer that, I can use a single interrupt - and
just ignore the second one defined in DT (and also remove it from the
config structure for board files).

Thanks,
Bartosz

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