From mboxrd@z Thu Jan 1 00:00:00 1970 From: v1ron@mail.ru (Roman Volkov) Date: Mon, 21 Dec 2015 23:33:59 +0300 Subject: [PATCH 0/4] clocksource/vt8500: Fix hangs in small delays In-Reply-To: <20151221112916.40373d2f@anonymous> References: <1450650492-18996-1-git-send-email-v1ron@mail.ru> <20151221112916.40373d2f@anonymous> Message-ID: <20151221233359.268fe6da@anonymous> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org > Roman Volkov mail.ru> writes: > > > > > From: Roman Volkov 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? I don't think maintainers will accept a lot of #ifdefs. I have an idea to move the common code from the PXA to something like pxa_common.c (can we give the correct name for it?) and include it from the vt8500_timer.c and pxa_timer.c. > 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. Sure. But lets make the vt8500 working at this step. > > 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 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 > > -38,36 +38,75 > > > > #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? If we do the merging work with PXA, this code will go away. Have this variable already fixed some _real_ problem? Otherwise this is excessive coding. > > #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? Oh my right-handed habits :) > 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. When we perform our merging work, we have to use the following glue: ... vt8500_timer_read { ... } #define timer_read(reg) vt8500_timer_read(reg) ... #include pxa_common.c > > > > -75,23 +114,24 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? To avoid calculation of the 64-bit cycle_t and remove type casts. > > - 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.