ARC: Fix __udelay calculation

commit 7efd0da2d17360e1cef91507dbe619db0ee2c691 upstream.

Cast usecs to u64, to ensure that the (usecs * 4295 * HZ)
multiplication is 64 bit.

Initially, the (usecs * 4295 * HZ) part was done as a 32 bit
multiplication, with the result casted to 64 bit. This led to some bits
falling off, causing a "DMA initialization error" in the stmmac Ethernet
driver, due to a premature timeout.

Signed-off-by: Mischa Jonker <mjonker@synopsys.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 2 insertions, 3 deletions

diff --git a/arch/arc/include/asm/delay.h b/arch/arc/include/asm/delay.h
index 442ce5d0f709..43de30256981 100644
--- a/arch/arc/include/asm/delay.h
+++ b/arch/arc/include/asm/delay.h
@@ -53,11 +53,10 @@ static inline void __udelay(unsigned long usecs)
 {
         unsigned long loops;
 
-        /* (long long) cast ensures 64 bit MPY - real or emulated
+        /* (u64) cast ensures 64 bit MPY - real or emulated
          * HZ * 4295 is pre-evaluated by gcc - hence only 2 mpy ops
          */
-        loops = ((long long)(usecs * 4295 * HZ) *
-                 (long long)(loops_per_jiffy)) >> 32;
+        loops = ((u64) usecs * 4295 * HZ * loops_per_jiffy) >> 32;
 
         __delay(loops);
 }