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ARM: MX51: PLL errata workaround

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This is a port of the official PLL errata workaround from Freescale to
mainline u-boot.
The PLL's in the i.MX51 processor can go out of lock due to a metastable
condition in an analog flip-flop when used at high frequencies.
This workaround implements an undocumented feature in the PLL (dither
mode), which causes the effect of this failure to be much lower (in terms
of frequency deviation), avoiding system failure, or at least decreasing
the likelihood of system failure.

Signed-off-by: David Jander <david@protonic.nl>
This commit is contained in:
David Jander 2011-07-13 21:11:53 +00:00 committed by Albert ARIBAUD
parent 96c9745fa1
commit 9db1bfa110
3 changed files with 60 additions and 0 deletions
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38
arch/arm/cpu/armv7/mx5/lowlevel_init.S
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@ -121,6 +121,35 @@
beq 1b
.endm
.macro setup_pll_errata pll, freq
ldr r2, =\pll
mov r1, #0x0
str r1, [r2, #PLL_DP_CONFIG] /* Disable auto-restart AREN bit */
ldr r1, =0x00001236
str r1, [r2, #PLL_DP_CTL] /* Restart PLL with PLM=1 */
1: ldr r1, [r2, #PLL_DP_CTL] /* Wait for lock */
ands r1, r1, #0x1
beq 1b
ldr r5, \freq
str r5, [r2, #PLL_DP_MFN] /* Modify MFN value */
str r5, [r2, #PLL_DP_HFS_MFN]
mov r1, #0x1
str r1, [r2, #PLL_DP_CONFIG] /* Reload MFN value */
2: ldr r1, [r2, #PLL_DP_CONFIG]
tst r1, #1
bne 2b
ldr r1, =100 /* Wait at least 4 us */
3: subs r1, r1, #1
bge 3b
mov r1, #0x2
str r1, [r2, #PLL_DP_CONFIG] /* Enable auto-restart AREN bit */
.endm
.macro init_clock
ldr r0, =CCM_BASE_ADDR
@ -157,7 +186,12 @@
mov r1, #0x4
str r1, [r0, #CLKCTL_CCSR]
#if defined(CONFIG_MX51_PLL_ERRATA)
setup_pll PLL1_BASE_ADDR, 864
setup_pll_errata PLL1_BASE_ADDR, W_DP_MFN_800_DIT
#else
setup_pll PLL1_BASE_ADDR, 800
#endif
#if defined(CONFIG_MX51)
setup_pll PLL3_BASE_ADDR, 665
@ -287,6 +321,10 @@ lowlevel_init:
mov pc,lr
/* Board level setting value */
W_DP_OP_864: .word DP_OP_864
W_DP_MFD_864: .word DP_MFD_864
W_DP_MFN_864: .word DP_MFN_864
W_DP_MFN_800_DIT: .word DP_MFN_800_DIT
W_DP_OP_800: .word DP_OP_800
W_DP_MFD_800: .word DP_MFD_800
W_DP_MFN_800: .word DP_MFN_800

5
arch/arm/include/asm/arch-mx5/imx-regs.h
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@ -235,6 +235,11 @@
/* Assuming 24MHz input clock with doubler ON */
/* MFI PDF */
#define DP_OP_864 ((8 << 4) + ((1 - 1) << 0))
#define DP_MFD_864 (180 - 1) /* PL Dither mode */
#define DP_MFN_864 180
#define DP_MFN_800_DIT 60 /* PL Dither mode */
#define DP_OP_850 ((8 << 4) + ((1 - 1) << 0))
#define DP_MFD_850 (48 - 1)
#define DP_MFN_850 41

17
doc/README.imx5 Normal file
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@ -0,0 +1,17 @@
U-Boot for Freescale i.MX5x
This file contains information for the port of U-Boot to the Freescale
i.MX5x SoCs.
1. CONFIGURATION OPTIONS/SETTINGS
---------------------------------
1.1 CONFIG_MX51_PLL_ERRATA: Workaround for i.MX51 PLL errata.
This option should be enabled by all boards using the i.MX51 silicon
version up until (including) 3.0 running at 800MHz.
The PLL's in the i.MX51 processor can go out of lock due to a metastable
condition in an analog flip-flop when used at high frequencies.
This workaround implements an undocumented feature in the PLL (dither
mode), which causes the effect of this failure to be much lower (in terms
of frequency deviation), avoiding system failure, or at least decreasing
the likelihood of system failure.