On Mon, 12 Nov 2018, Geert Uytterhoeven wrote:
> Hi Finn,
>
> On Mon, Nov 12, 2018 at 5:46 AM Finn Thain <fth...@telegraphics.com.au> wrote:
> > Add a platform clocksource by adapting the existing arch_gettimeoffset
> > implementation.
> >
> > Signed-off-by: Finn Thain <fth...@telegraphics.com.au>
>
> Thanks for your patch!
>
Thanks for your review.
> > --- a/arch/m68k/amiga/config.c
> > +++ b/arch/m68k/amiga/config.c
> > @@ -17,6 +17,7 @@
> > #include <linux/mm.h>
> > #include <linux/seq_file.h>
> > #include <linux/tty.h>
> > +#include <linux/clocksource.h>
> > #include <linux/console.h>
> > #include <linux/rtc.h>
> > #include <linux/init.h>
> > @@ -461,7 +462,30 @@ void __init config_amiga(void)
> > *(unsigned char *)ZTWO_VADDR(0xde0002) |= 0x80;
> > }
> >
> > +static u64 amiga_read_clk(struct clocksource *cs);
> > +
> > +static struct clocksource amiga_clk = {
> > + .name = "ciab",
> > + .rating = 250,
> > + .read = amiga_read_clk,
> > + .mask = CLOCKSOURCE_MASK(32),
> > + .flags = CLOCK_SOURCE_IS_CONTINUOUS,
> > +};
> > +
> > static unsigned short jiffy_ticks;
> > +static u32 clk_total;
>
> Shouldn't clk_total be u64?
>
Well, it was intentionally u32, and amiga_clk.mask was intentionally
CLOCKSOURCE_MASK(32)...
> > +
> > +static irqreturn_t ciab_timer_handler(int irq, void *data)
> > +{
> > + irq_handler_t timer_routine = data;
> > + unsigned long flags;
> > +
> > + local_irq_save(flags);
> > + clk_total += jiffy_ticks;
> > + local_irq_restore(flags);
> > +
> > + return timer_routine(irq, data);
> > +}
>
> [...]
>
> > -static u32 amiga_gettimeoffset(void)
> > +static u64 amiga_read_clk(struct clocksource *cs)
> > {
> > unsigned long flags;
> > unsigned short hi, lo, hi2;
> > @@ -512,14 +537,13 @@ static u32 amiga_gettimeoffset(void)
> > if (ticks > jiffy_ticks / 2)
> > /* check for pending interrupt */
> > if (cia_set_irq(&ciab_base, 0) & CIA_ICR_TA)
> > - offset = 10000;
> > + offset = jiffy_ticks;
> >
> > local_irq_restore(flags);
> >
> > ticks = jiffy_ticks - ticks;
> > - ticks = (10000 * ticks) / jiffy_ticks;
> >
> > - return (ticks + offset) * 1000;
> > + return clk_total + ticks + offset;
>
> ... to return a full 64-bit value here?
>
It's certainly possible. Is it better? It sounds like a question about the
cost of wrap-around in the clocksource core vs. the cost of 64-bit
additions in the arch code.
Looking at __clocksource_update_freq_scale() there are some consequences
to choosing a 32-bit mask --
* For clocksources which have a mask > 32-bit
* we need to limit the max sleep time to have a good
* conversion precision.
I don't know the answer, sorry.
--
> Gr{oetje,eeting}s,
>
> Geert
>
>
