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

[Laurent Vivier]

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@xxxxxxxxx>
> > > ---
> > >   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