linux-kernel - Re: [PATCH v15 4/5] clocksource/drivers: Add a goldfish-timer clocksource

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Message-ID: <465da893-4e7b-33e4-2859-032724bae42f@vivier.eu>
Date:   Wed, 6 Apr 2022 13:26:33 +0200
From:   Laurent Vivier <laurent@...ier.eu>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:     Jiaxun Yang <jiaxun.yang@...goat.com>,
        Alessandro Zummo <a.zummo@...ertech.it>,
        linux-rtc@...r.kernel.org, Stephen Boyd <sboyd@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        linux-m68k@...ts.linux-m68k.org,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        John Stultz <john.stultz@...aro.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v15 4/5] clocksource/drivers: Add a goldfish-timer
 clocksource

Le 06/04/2022 à 12:27, Daniel Lezcano a écrit :
> 
> Hi Laurent,
> 
> 
> On 01/04/2022 12:20, Laurent Vivier wrote:
>>
>> Daniel ?
>>
>> Thanks,
>> Laurent
>>
>> Le 10/03/2022 à 10:00, Laurent Vivier a écrit :
>>> Add a clocksource based on the goldfish-rtc device.
>>>
>>> Move the timer register definition to <clocksource/timer-goldfish.h>
>>>
>>> This kernel implementation is based on the QEMU upstream implementation:
>>>
>>>     https://git.qemu.org/?p=qemu.git;a=blob_plain;f=hw/rtc/goldfish_rtc.c
>>>
>>> goldfish-timer is a high-precision signed 64-bit nanosecond timer.
>>> It is part of the 'goldfish' virtual hardware platform used to run
>>> some emulated Android systems under QEMU.
>>> This timer only supports oneshot event.
>>>
>>> Signed-off-by: Laurent Vivier <laurent@...ier.eu>
>>> ---
>>>   drivers/clocksource/Kconfig          |   7 ++
>>>   drivers/clocksource/Makefile         |   1 +
>>>   drivers/clocksource/timer-goldfish.c | 153 +++++++++++++++++++++++++++
>>>   drivers/rtc/rtc-goldfish.c           |  13 +--
>>>   include/clocksource/timer-goldfish.h |  31 ++++++
>>>   5 files changed, 193 insertions(+), 12 deletions(-)
>>>   create mode 100644 drivers/clocksource/timer-goldfish.c
>>>   create mode 100644 include/clocksource/timer-goldfish.h
>>>
>>> diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
>>> index cfb8ea0df3b1..94f00374cebb 100644
>>> --- a/drivers/clocksource/Kconfig
>>> +++ b/drivers/clocksource/Kconfig
>>> @@ -721,4 +721,11 @@ config MICROCHIP_PIT64B
>>>         modes and high resolution. It is used as a clocksource
>>>         and a clockevent.
>>> +config GOLDFISH_TIMER
>>> +    bool "Clocksource using goldfish-rtc"
>>> +    depends on M68K || COMPILE_TEST
>>> +    depends on RTC_DRV_GOLDFISH
>>> +    help
>>> +      Support for the timer/counter of goldfish-rtc
>>> +
>>>   endmenu
>>> diff --git a/drivers/clocksource/Makefile b/drivers/clocksource/Makefile
>>> index fa5f624eadb6..12f5d7e8cc2d 100644
>>> --- a/drivers/clocksource/Makefile
>>> +++ b/drivers/clocksource/Makefile
>>> @@ -89,3 +89,4 @@ obj-$(CONFIG_GX6605S_TIMER)        += timer-gx6605s.o
>>>   obj-$(CONFIG_HYPERV_TIMER)        += hyperv_timer.o
>>>   obj-$(CONFIG_MICROCHIP_PIT64B)        += timer-microchip-pit64b.o
>>>   obj-$(CONFIG_MSC313E_TIMER)        += timer-msc313e.o
>>> +obj-$(CONFIG_GOLDFISH_TIMER)        += timer-goldfish.o
>>> diff --git a/drivers/clocksource/timer-goldfish.c b/drivers/clocksource/timer-goldfish.c
>>> new file mode 100644
>>> index 000000000000..0512d5eabc82
>>> --- /dev/null
>>> +++ b/drivers/clocksource/timer-goldfish.c
>>> @@ -0,0 +1,153 @@
>>> +// SPDX-License-Identifier: GPL-2.0
>>> +
>>> +#include <linux/interrupt.h>
>>> +#include <linux/ioport.h>
>>> +#include <linux/clocksource.h>
>>> +#include <linux/clockchips.h>
>>> +#include <linux/module.h>
>>> +#include <linux/slab.h>
>>> +#include <linux/goldfish.h>
> 
> Not related to this patch: would it make sense to move it to linux/soc/... ?

I don't know. goldfish is not really a soc. I didn't really find a good place where it should be.

> 
> 
>>> +#include <clocksource/timer-goldfish.h>
>>> +
>>> +struct goldfish_timer {
>>> +    struct clocksource cs;
>>> +    struct clock_event_device ced;
>>> +    struct resource res;
>>> +    void __iomem *base;
>>> +};
>>> +
>>> +static struct goldfish_timer *ced_to_gf(struct clock_event_device *ced)
>>> +{
>>> +    return container_of(ced, struct goldfish_timer, ced);
>>> +}
>>> +
>>> +static struct goldfish_timer *cs_to_gf(struct clocksource *cs)
>>> +{
>>> +    return container_of(cs, struct goldfish_timer, cs);
>>> +}
>>> +
>>> +static u64 goldfish_timer_read(struct clocksource *cs)
>>> +{
>>> +    struct goldfish_timer *timerdrv = cs_to_gf(cs);
>>> +    void __iomem *base = timerdrv->base;
>>> +    u32 time_low, time_high;
>>> +    u64 ticks;
>>> +
>>> +    /*
>>> +     * time_low: get low bits of current time and update time_high
>>> +     * time_high: get high bits of time at last time_low read
>>> +     */
>>> +    time_low = gf_ioread32(base + TIMER_TIME_LOW);
>>> +    time_high = gf_ioread32(base + TIMER_TIME_HIGH);
> 
> There is a risk here to have the counter rolling over between low and high reading, no ?

No, because value of high is frozen when we read low, so the 64bit value doesn't move between the 
two ioread32().

Thanks,
Laurent