Messages in this thread | | | From | Alexey Charkov <> | Subject | Re: [PATCH 4/4] clocksource/vt8500: Add register R/W functions | Date | Mon, 21 Dec 2015 09:54:36 +0000 (UTC) |
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Roman Volkov <v1ron <at> mail.ru> writes:
> > From: Roman Volkov <rvolkov <at> v1ros.org> > > vt8500 timer requires special synchronization for accessing some of its > registers. Define special read and write functions to handle this process > transparently.
Maybe introduce such accessor functions (conditionally) into the PXA driver and kill this one altogether then?
If I understood you right, this extra bus synchronization is the only thing that makes vt8500 different from PXA, so merging the two files right away might be a better long-term option.
> To perform a read from the Timer Count register, user must write a one > to the Timer Control register and wait for completion flag by polling the > Timer Read Count Active bit. > > To perform a write to the Count or Match registers, user must poll the > write completion flag for the corresponding register to ensure that the > previous write completed and then write the actual value. > > Signed-off-by: Roman Volkov <rvolkov <at> v1ros.org> > --- > drivers/clocksource/vt8500_timer.c | 90 +++++++++++++++++++++++++++----------- > 1 file changed, 65 insertions(+), 25 deletions(-) > > diff --git a/drivers/clocksource/vt8500_timer.c b/drivers/clocksource/vt8500_timer.c > index 7649852..4d7513f 100644 > --- a/drivers/clocksource/vt8500_timer.c > +++ b/drivers/clocksource/vt8500_timer.c > <at> <at> -38,36 +38,75 <at> <at> > > #define VT8500_TIMER_OFFSET 0x0100 > #define VT8500_TIMER_HZ 3000000 > -#define TIMER_MATCH_VAL 0x0000 > +#define TIMER_MATCH0_VAL 0 > +#define TIMER_MATCH1_VAL 0x04 > +#define TIMER_MATCH2_VAL 0x08 > +#define TIMER_MATCH3_VAL 0x0c > #define TIMER_COUNT_VAL 0x0010 > #define TIMER_STATUS_VAL 0x0014 > #define TIMER_IER_VAL 0x001c /* interrupt enable */ > #define TIMER_CTRL_VAL 0x0020 > #define TIMER_AS_VAL 0x0024 /* access status */ > -#define TIMER_COUNT_R_ACTIVE (1 << 5) /* not ready for read */ > -#define TIMER_COUNT_W_ACTIVE (1 << 4) /* not ready for write */ > -#define TIMER_MATCH_W_ACTIVE (1 << 0) /* not ready for write */ > - > -#define timer_readl(addr) readl_relaxed(regbase + addr) > -#define timer_writel(v, addr) writel_relaxed(v, regbase + addr) > +/* R/W status flags */ > +#define TIMER_COUNT_R_ACTIVE (1 << 5) > +#define TIMER_COUNT_W_ACTIVE (1 << 4) > +#define TIMER_MATCH3_W_ACTIVE (1 << 3) > +#define TIMER_MATCH2_W_ACTIVE (1 << 2) > +#define TIMER_MATCH1_W_ACTIVE (1 << 1) > +#define TIMER_MATCH0_W_ACTIVE (1 << 0) > + > +#define vt8500_timer_sync(bit) { while (readl_relaxed \ > + (regbase + TIMER_AS_VAL) & bit) \ > + cpu_relax(); }
The whole issue around 'loops' counter in these busy waits basically boils down to whether we would like a way to try and recover from a potential hardware misbehavior.
You can of course argue that when the system timer misbehaves you already have bigger issues to worry about, but does a 10 msec limit that was in the original version really hurt?
> #define MIN_OSCR_DELTA 16 > > static void __iomem *regbase; > > -static cycle_t vt8500_timer_read(struct clocksource *cs) > +static void vt8500_timer_write(unsigned long reg, u32 value)
Maybe define this with 'value' first, 'reg' second - to be in line with the common prototype of writel and such?
Plus if you could take the same name for the macro above (timer_writel) and this accessor (vt8500_timer_write) that would somewhat reduce extra additions/deletions in this patch. Same for the read function.
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> <at> <at> -75,23 +114,24 <at> <at> static struct clocksource clocksource = { > static int vt8500_timer_set_next_event(unsigned long cycles, > struct clock_event_device *evt) > { > - cycle_t alarm = clocksource.read(&clocksource) + cycles; > - while (timer_readl(TIMER_AS_VAL) & TIMER_MATCH_W_ACTIVE) > - cpu_relax(); > - timer_writel((unsigned long)alarm, TIMER_MATCH_VAL); > + unsigned long alarm = vt8500_timer_read(TIMER_COUNT_VAL) + cycles;
I personally like the form above better (via clocksource.read) - even if just for the fact that it's shorter and reduces the number of places where we use TIMER_COUNT_VAL definition.
Any specific reasons to rewrite it?
> - if ((signed)(alarm - clocksource.read(&clocksource)) <= MIN_OSCR_DELTA) > + vt8500_timer_write(TIMER_MATCH0_VAL, alarm); > + if ((signed)(alarm - vt8500_timer_read( > + TIMER_COUNT_VAL)) <= MIN_OSCR_DELTA) {
Same here.
<skip>
Best regards, Alexey
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