From: Alexey Charkov <alchark@gmail.com>
To: linux-kernel@vger.kernel.org
Subject: Re: [PATCH 4/4] clocksource/vt8500: Add register R/W functions
Date: Mon, 21 Dec 2015 09:54:36 +0000 (UTC) [thread overview]
Message-ID: <loom.20151221T103308-220@post.gmane.org> (raw)
In-Reply-To: 1450650492-18996-5-git-send-email-v1ron@mail.ru
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.
<skip>
> <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
next prev parent reply other threads:[~2015-12-21 10:00 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-12-20 22:28 [PATCH 0/4] clocksource/vt8500: Fix hangs in small delays Roman Volkov
2015-12-20 22:28 ` Roman Volkov
2015-12-20 22:28 ` [PATCH 1/4] clocksource/vt8500: Use [read\write]l_relaxed() Roman Volkov
2015-12-20 22:28 ` Roman Volkov
2015-12-20 22:28 ` [PATCH 2/4] clocksource/vt8500: Remove the 'loops' variable Roman Volkov
2015-12-20 22:28 ` Roman Volkov
2015-12-20 22:28 ` [PATCH 3/4] clocksource/vt8500: Use MIN_OSCR_DELTA from PXA Roman Volkov
2015-12-20 22:28 ` Roman Volkov
2015-12-20 22:28 ` [PATCH 4/4] clocksource/vt8500: Add register R/W functions Roman Volkov
2015-12-20 22:28 ` Roman Volkov
2015-12-21 9:54 ` Alexey Charkov [this message]
2015-12-21 8:29 ` [PATCH 0/4] clocksource/vt8500: Fix hangs in small delays Roman Volkov
2015-12-21 8:29 ` Roman Volkov
2015-12-21 20:33 ` Roman Volkov
2015-12-21 20:33 ` Roman Volkov
2015-12-22 9:09 ` Alexey Charkov
2015-12-22 9:09 ` Alexey Charkov
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