[U-Boot] [PATCH] ARM: global_data: make tbl long long

[U-Boot] [PATCH] ARM: global_data: make tbl long long

[Dirk Behme]

From: Dirk Behme <dirk.behme@de.bosch.com>

Several ARM timer implementations use gd->arch.tbl to record the
absolute tick count of 32-bit counters, including timer overflows.
For example arch/arm/imx-common/timer.c does:

ulong lastinc;
ulong now = counter value;
if (no overflow) {
	...
} else { /* counter overflow */
	gd->arch.tbl += (0xFFFFFFFF - lastinc) + now;
}
lastinc =  now;

As we use a 32-bit counter and the two ulong (32-bit) variables 'lastinc'
and 'now' here, gd->arch.tbl should be long long (64-bit) to not overflow
at the same time, too.

Signed-off-by: Knut Wohlrab <knut.wohlrab@de.bosch.com>
Signed-off-by: Dirk Behme <dirk.behme@de.bosch.com>
---
 arch/arm/include/asm/global_data.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm/include/asm/global_data.h b/arch/arm/include/asm/global_data.h
index 37ac0da..1099af9 100644
--- a/arch/arm/include/asm/global_data.h
+++ b/arch/arm/include/asm/global_data.h
@@ -41,7 +41,7 @@ struct arch_global_data {
 	/* "static data" needed by most of timer.c on ARM platforms */
 	unsigned long timer_rate_hz;
 	unsigned long tbu;
-	unsigned long tbl;
+	unsigned long long tbl;
 	unsigned long lastinc;
 	unsigned long long timer_reset_value;
 #ifdef CONFIG_IXP425
-- 
1.7.10.4

[U-Boot] [PATCH] ARM: global_data: make tbl long long

[Wolfgang Denk]

Dear Dirk Behme,

In message <1362387637-32334-1-git-send-email-dirk.behme@de.bosch.com> you wrote:
> From: Dirk Behme <dirk.behme@de.bosch.com>
> 
> Several ARM timer implementations use gd->arch.tbl to record the
> absolute tick count of 32-bit counters, including timer overflows.
> For example arch/arm/imx-common/timer.c does:
> 
> ulong lastinc;
> ulong now = counter value;
> if (no overflow) {
> 	...
> } else { /* counter overflow */
> 	gd->arch.tbl += (0xFFFFFFFF - lastinc) + now;
> }
> lastinc =  now;
> 
> As we use a 32-bit counter and the two ulong (32-bit) variables 'lastinc'
> and 'now' here, gd->arch.tbl should be long long (64-bit) to not overflow
> at the same time, too.

I think this is wrong.

"tbl" means "time base, lower 32 bits" and is complemented by "tbu"
(time base, upper 32 bits) to form a 64 bit time base counter.

If you need the full 64 bit precision, then please either maintain the
carry manually, or use a proper union or similar.

Best regards,

Wolfgang Denk

-- 
DENX Software Engineering GmbH,     MD: Wolfgang Denk & Detlev Zundel
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
A consultant is a person who borrows your watch, tells you what  time
it is, pockets the watch, and sends you a bill for it.

[U-Boot] [PATCH] ARM: global_data: make tbl long long

[Dirk Behme]

Dear Wolfgang,

On 04.03.2013 12:10, Wolfgang Denk wrote:
> Dear Dirk Behme,
> 
> In message <1362387637-32334-1-git-send-email-dirk.behme@de.bosch.com> you wrote:
>> From: Dirk Behme <dirk.behme@de.bosch.com>
>>
>> Several ARM timer implementations use gd->arch.tbl to record the
>> absolute tick count of 32-bit counters, including timer overflows.
>> For example arch/arm/imx-common/timer.c does:
>>
>> ulong lastinc;
>> ulong now = counter value;
>> if (no overflow) {
>> 	...
>> } else { /* counter overflow */
>> 	gd->arch.tbl += (0xFFFFFFFF - lastinc) + now;
>> }
>> lastinc =  now;
>>
>> As we use a 32-bit counter and the two ulong (32-bit) variables 'lastinc'
>> and 'now' here, gd->arch.tbl should be long long (64-bit) to not overflow
>> at the same time, too.
> 
> I think this is wrong.
> 
> "tbl" means "time base, lower 32 bits" and is complemented by "tbu"
> (time base, upper 32 bits) to form a 64 bit time base counter.
> 
> If you need the full 64 bit precision, then please either maintain the
> carry manually, or use a proper union or similar.

Many thanks for this explanation!

This patch is obsolete now, replaced by

http://patchwork.ozlabs.org/patch/224740/

Thanks

Dirk

[U-Boot] [PATCH] ARM: global_data: make tbl long long

[Wolfgang Denk]

Dear Dirk,

In message <5134ADB7.2000106@de.bosch.com> you wrote:
> 
> Many thanks for this explanation!

You are welcome...

> This patch is obsolete now, replaced by
> 
> http://patchwork.ozlabs.org/patch/224740/

Thanks, looks good to me.  I hesitate to add an Acked-by: or even
Reviewed-by: as this timer stuff on ARM is a bit of black magic to
me...

Best regards,

Wolfgang Denk

-- 
DENX Software Engineering GmbH,     MD: Wolfgang Denk & Detlev Zundel
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
Unix: Some say the learning curve is steep,  but  you  only  have  to
climb it once.                                      - Karl Lehenbauer