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orion5x: optimize window size computation

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Signed-off-by: Chris Moore <moore@free.fr>
Signed-off-by: Albert Aribaud <albert.aribaud@free.fr>
This commit is contained in:
Albert Aribaud 2010-10-07 20:19:53 +05:30 committed by Prafulla Wadaskar
parent 35883cca8a
commit 3b467ec444
1 changed files with 21 additions and 11 deletions
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32
arch/arm/cpu/arm926ejs/orion5x/cpu.c
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@ -48,24 +48,34 @@ void reset_cpu(unsigned long ignored)
}
/*
* Window Size
* Compute Window Size field value from size expressed in bytes
* Used with the Base register to set the address window size and location.
* Must be programmed from LSB to MSB as sequence of ones followed by
* sequence of zeros. The number of ones specifies the size of the window in
* 64 KByte granularity (e.g., a value of 0x00FF specifies 256 = 16 MByte).
* NOTE: A value of 0x0 specifies 64-KByte size.
* 64 KiB granularity (e.g., a value of 0x00FF specifies 256 = 16 MiB).
* NOTES:
* 1) A sizeval equal to 0x0 specifies 4 GiB.
* 2) A return value of 0x0 specifies 64 KiB.
*/
unsigned int orion5x_winctrl_calcsize(unsigned int sizeval)
{
int i;
unsigned int j = 0;
u32 val = sizeval >> 1;
/*
* Calculate the number of 64 KiB blocks needed minus one (rounding up).
* For sizeval > 0 this is equivalent to:
* sizeval = (u32) ceil((double) sizeval / 65536.0) - 1
*/
sizeval = (sizeval - 1) >> 16;
for (i = 0; val >= 0x10000; i++) {
j |= (1 << i);
val = val >> 1;
}
return 0x0000ffff & j;
/*
* Propagate 'one' bits to the right by 'oring' them.
* We need only treat bits 15-0.
*/
sizeval |= sizeval >> 1; /* 'Or' bit 15 onto bit 14 */
sizeval |= sizeval >> 2; /* 'Or' bits 15-14 onto bits 13-12 */
sizeval |= sizeval >> 4; /* 'Or' bits 15-12 onto bits 11-8 */
sizeval |= sizeval >> 8; /* 'Or' bits 15-8 onto bits 7-0*/
return sizeval;
}
/*