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authorLinus Walleij <linus.walleij@linaro.org>2016-02-08 09:14:37 +0100
committerRussell King <rmk+kernel@arm.linux.org.uk>2016-02-08 16:40:36 +0000
commit5070fb14a0154f075c8b418e5bc58a620ae85a45 (patch)
tree71eda55c9a5647635fe8f01b5caec276877dff89 /arch/arm/common
parent03590cb56d5df7367ccb9e6e0127593254401c42 (diff)
ARM: 8517/1: ICST: avoid arithmetic overflow in icst_hz()
When trying to set the ICST 307 clock to 25174000 Hz I ran into this arithmetic error: the icst_hz_to_vco() correctly figure out DIVIDE=2, RDW=100 and VDW=99 yielding a frequency of 25174000 Hz out of the VCO. (I replicated the icst_hz() function in a spreadsheet to verify this.) However, when I called icst_hz() on these VCO settings it would instead return 4122709 Hz. This causes an error in the common clock driver for ICST as the common clock framework will call .round_rate() on the clock which will utilize icst_hz_to_vco() followed by icst_hz() suggesting the erroneous frequency, and then the clock gets set to this. The error did not manifest in the old clock framework since this high frequency was only used by the CLCD, which calls clk_set_rate() without first calling clk_round_rate() and since the old clock framework would not call clk_round_rate() before setting the frequency, the correct values propagated into the VCO. After some experimenting I figured out that it was due to a simple arithmetic overflow: the divisor for 24Mhz reference frequency as reference becomes 24000000*2*(99+8)=0x132212400 and the "1" in bit 32 overflows and is lost. But introducing an explicit 64-by-32 bit do_div() and casting the divisor into (u64) we get the right frequency back, and the right frequency gets set. Tested on the ARM Versatile. Cc: stable@vger.kernel.org Cc: linux-clk@vger.kernel.org Cc: Pawel Moll <pawel.moll@arm.com> Signed-off-by: Linus Walleij <linus.walleij@linaro.org> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Diffstat (limited to 'arch/arm/common')
-rw-r--r--arch/arm/common/icst.c8
1 files changed, 6 insertions, 2 deletions
diff --git a/arch/arm/common/icst.c b/arch/arm/common/icst.c
index 2dc6da70ae59..d3c0e69df259 100644
--- a/arch/arm/common/icst.c
+++ b/arch/arm/common/icst.c
@@ -16,7 +16,7 @@
*/
#include <linux/module.h>
#include <linux/kernel.h>
-
+#include <asm/div64.h>
#include <asm/hardware/icst.h>
/*
@@ -29,7 +29,11 @@ EXPORT_SYMBOL(icst525_s2div);
unsigned long icst_hz(const struct icst_params *p, struct icst_vco vco)
{
- return p->ref * 2 * (vco.v + 8) / ((vco.r + 2) * p->s2div[vco.s]);
+ u64 dividend = p->ref * 2 * (u64)(vco.v + 8);
+ u32 divisor = (vco.r + 2) * p->s2div[vco.s];
+
+ do_div(dividend, divisor);
+ return (unsigned long)dividend;
}
EXPORT_SYMBOL(icst_hz);