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linux/arch/arm/mach-omap2/sram34xx.S
Jon Hunter a3fed9bc18 omap3: Prevent SDRC deadlock when L3 is changing frequency 
When changing the L3 clock frequency, the CPU is executing from internal RAM
and the SDRC clock is disabled. During this time accesses made to external
DDR are stalled. If the ARM subsystem attempts to access the DDR while the
SDRC clock is disabled this will stall the CPU until the access to the SDRC
timeouts. A timeout on the SDRC should never occur. Once a timeout occurs all
the following accesses will be aborted and the DDR is no longer accessible.

Although the code being executed in the internal RAM does not directly access
the DDR, it was found that the branch prediction logic in the CPU may cause
the CPU to prefetch code from a DDR location while the SDRC clock is disabled.
This was causing an SDRC timeout which resulted in a system hang.

This patch fixes this problem by ensuring the branch prediction logic is
disabled while changing the L3 clock frequency. The branch prediction logic
is disabled by clearing the Z-bit in the ARM CTRL register.

Disabling the branch prediction logic does not have any noticable impact
on the execution time of this code section. The hardware observability
signals were used to monitor the sdrc idle time with and without this
patch when operating at different CPU frequencies (150MHz, 500MHz and
600MHz) and the total sdrc idle time when changing frequenct was in
the range of 9-11us. This was measured on an omap3430 SDP running the
omapzoom p-android-omap-2.6.29 branch.

Signed-off-by: Jon Hunter <jon-hunter@ti.com>
Signed-off-by: Paul Walmsley <paul@pwsan.com>
Cc: Santosh Shilimkar <santosh.shilimkar@ti.com>
Cc: Richard Woodruff <r-woodruff2@ti.com>
Cc: Tony Lindgren <tony@atomide.com>
2010-09-27 14:02:59 -06:00

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/*
* linux/arch/arm/mach-omap3/sram.S
*
* Omap3 specific functions that need to be run in internal SRAM
*
* Copyright (C) 2004, 2007, 2008 Texas Instruments, Inc.
* Copyright (C) 2008 Nokia Corporation
*
* Rajendra Nayak <rnayak@ti.com>
* Richard Woodruff <r-woodruff2@ti.com>
* Paul Walmsley
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License as
* published by the Free Software Foundation; either version 2 of
* the License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR /PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston,
* MA 02111-1307 USA
*/
#include <linux/linkage.h>
#include <asm/assembler.h>
#include <mach/hardware.h>
#include <mach/io.h>
#include "sdrc.h"
#include "cm.h"
.text
/* r1 parameters */
#define SDRC_NO_UNLOCK_DLL 0x0
#define SDRC_UNLOCK_DLL 0x1
/* SDRC_DLLA_CTRL bit settings */
#define FIXEDDELAY_SHIFT 24
#define FIXEDDELAY_MASK (0xff << FIXEDDELAY_SHIFT)
#define DLLIDLE_MASK 0x4
/*
* SDRC_DLLA_CTRL default values: TI hardware team indicates that
* FIXEDDELAY should be initialized to 0xf. This apparently was
* empirically determined during process testing, so no derivation
* was provided.
*/
#define FIXEDDELAY_DEFAULT (0x0f << FIXEDDELAY_SHIFT)
/* SDRC_DLLA_STATUS bit settings */
#define LOCKSTATUS_MASK 0x4
/* SDRC_POWER bit settings */
#define SRFRONIDLEREQ_MASK 0x40
/* CM_IDLEST1_CORE bit settings */
#define ST_SDRC_MASK 0x2
/* CM_ICLKEN1_CORE bit settings */
#define EN_SDRC_MASK 0x2
/* CM_CLKSEL1_PLL bit settings */
#define CORE_DPLL_CLKOUT_DIV_SHIFT 0x1b
/*
* omap3_sram_configure_core_dpll - change DPLL3 M2 divider
*
* Params passed in registers:
* r0 = new M2 divider setting (only 1 and 2 supported right now)
* r1 = unlock SDRC DLL? (1 = yes, 0 = no). Only unlock DLL for
* SDRC rates < 83MHz
* r2 = number of MPU cycles to wait for SDRC to stabilize after
* reprogramming the SDRC when switching to a slower MPU speed
* r3 = increasing SDRC rate? (1 = yes, 0 = no)
*
* Params passed via the stack. The needed params will be copied in SRAM
* before use by the code in SRAM (SDRAM is not accessible during SDRC
* reconfiguration):
* new SDRC_RFR_CTRL_0 register contents
* new SDRC_ACTIM_CTRL_A_0 register contents
* new SDRC_ACTIM_CTRL_B_0 register contents
* new SDRC_MR_0 register value
* new SDRC_RFR_CTRL_1 register contents
* new SDRC_ACTIM_CTRL_A_1 register contents
* new SDRC_ACTIM_CTRL_B_1 register contents
* new SDRC_MR_1 register value
*
* If the param SDRC_RFR_CTRL_1 is 0, the parameters are not programmed into
* the SDRC CS1 registers
*
* NOTE: This code no longer attempts to program the SDRC AC timing and MR
* registers. This is because the code currently cannot ensure that all
* L3 initiators (e.g., sDMA, IVA, DSS DISPC, etc.) are not accessing the
* SDRAM when the registers are written. If the registers are changed while
* an initiator is accessing SDRAM, memory can be corrupted and/or the SDRC
* may enter an unpredictable state. In the future, the intent is to
* re-enable this code in cases where we can ensure that no initiators are
* touching the SDRAM. Until that time, users who know that their use case
* can satisfy the above requirement can enable the CONFIG_OMAP3_SDRC_AC_TIMING
* option.
*/
ENTRY(omap3_sram_configure_core_dpll)
stmfd sp!, {r1-r12, lr} @ store regs to stack
@ pull the extra args off the stack
@ and store them in SRAM
ldr r4, [sp, #52]
str r4, omap_sdrc_rfr_ctrl_0_val
ldr r4, [sp, #56]
str r4, omap_sdrc_actim_ctrl_a_0_val
ldr r4, [sp, #60]
str r4, omap_sdrc_actim_ctrl_b_0_val
ldr r4, [sp, #64]
str r4, omap_sdrc_mr_0_val
ldr r4, [sp, #68]
str r4, omap_sdrc_rfr_ctrl_1_val
cmp r4, #0 @ if SDRC_RFR_CTRL_1 is 0,
beq skip_cs1_params @ do not use cs1 params
ldr r4, [sp, #72]
str r4, omap_sdrc_actim_ctrl_a_1_val
ldr r4, [sp, #76]
str r4, omap_sdrc_actim_ctrl_b_1_val
ldr r4, [sp, #80]
str r4, omap_sdrc_mr_1_val
skip_cs1_params:
mrc p15, 0, r8, c1, c0, 0 @ read ctrl register
bic r10, r8, #0x800 @ clear Z-bit, disable branch prediction
mcr p15, 0, r10, c1, c0, 0 @ write ctrl register
dsb @ flush buffered writes to interconnect
isb @ prevent speculative exec past here
cmp r3, #1 @ if increasing SDRC clk rate,
bleq configure_sdrc @ program the SDRC regs early (for RFR)
cmp r1, #SDRC_UNLOCK_DLL @ set the intended DLL state
bleq unlock_dll
blne lock_dll
bl sdram_in_selfrefresh @ put SDRAM in self refresh, idle SDRC
bl configure_core_dpll @ change the DPLL3 M2 divider
mov r12, r2
bl wait_clk_stable @ wait for SDRC to stabilize
bl enable_sdrc @ take SDRC out of idle
cmp r1, #SDRC_UNLOCK_DLL @ wait for DLL status to change
bleq wait_dll_unlock
blne wait_dll_lock
cmp r3, #1 @ if increasing SDRC clk rate,
beq return_to_sdram @ return to SDRAM code, otherwise,
bl configure_sdrc @ reprogram SDRC regs now
return_to_sdram:
mcr p15, 0, r8, c1, c0, 0 @ restore ctrl register
isb @ prevent speculative exec past here
mov r0, #0 @ return value
ldmfd sp!, {r1-r12, pc} @ restore regs and return
unlock_dll:
ldr r11, omap3_sdrc_dlla_ctrl
ldr r12, [r11]
bic r12, r12, #FIXEDDELAY_MASK
orr r12, r12, #FIXEDDELAY_DEFAULT
orr r12, r12, #DLLIDLE_MASK
str r12, [r11] @ (no OCP barrier needed)
bx lr
lock_dll:
ldr r11, omap3_sdrc_dlla_ctrl
ldr r12, [r11]
bic r12, r12, #DLLIDLE_MASK
str r12, [r11] @ (no OCP barrier needed)
bx lr
sdram_in_selfrefresh:
ldr r11, omap3_sdrc_power @ read the SDRC_POWER register
ldr r12, [r11] @ read the contents of SDRC_POWER
mov r9, r12 @ keep a copy of SDRC_POWER bits
orr r12, r12, #SRFRONIDLEREQ_MASK @ enable self refresh on idle
str r12, [r11] @ write back to SDRC_POWER register
ldr r12, [r11] @ posted-write barrier for SDRC
idle_sdrc:
ldr r11, omap3_cm_iclken1_core @ read the CM_ICLKEN1_CORE reg
ldr r12, [r11]
bic r12, r12, #EN_SDRC_MASK @ disable iclk bit for SDRC
str r12, [r11]
wait_sdrc_idle:
ldr r11, omap3_cm_idlest1_core
ldr r12, [r11]
and r12, r12, #ST_SDRC_MASK @ check for SDRC idle
cmp r12, #ST_SDRC_MASK
bne wait_sdrc_idle
bx lr
configure_core_dpll:
ldr r11, omap3_cm_clksel1_pll
ldr r12, [r11]
ldr r10, core_m2_mask_val @ modify m2 for core dpll
and r12, r12, r10
orr r12, r12, r0, lsl #CORE_DPLL_CLKOUT_DIV_SHIFT
str r12, [r11]
ldr r12, [r11] @ posted-write barrier for CM
bx lr
wait_clk_stable:
subs r12, r12, #1
bne wait_clk_stable
bx lr
enable_sdrc:
ldr r11, omap3_cm_iclken1_core
ldr r12, [r11]
orr r12, r12, #EN_SDRC_MASK @ enable iclk bit for SDRC
str r12, [r11]
wait_sdrc_idle1:
ldr r11, omap3_cm_idlest1_core
ldr r12, [r11]
and r12, r12, #ST_SDRC_MASK
cmp r12, #0
bne wait_sdrc_idle1
restore_sdrc_power_val:
ldr r11, omap3_sdrc_power
str r9, [r11] @ restore SDRC_POWER, no barrier needed
bx lr
wait_dll_lock:
ldr r11, omap3_sdrc_dlla_status
ldr r12, [r11]
and r12, r12, #LOCKSTATUS_MASK
cmp r12, #LOCKSTATUS_MASK
bne wait_dll_lock
bx lr
wait_dll_unlock:
ldr r11, omap3_sdrc_dlla_status
ldr r12, [r11]
and r12, r12, #LOCKSTATUS_MASK
cmp r12, #0x0
bne wait_dll_unlock
bx lr
configure_sdrc:
ldr r12, omap_sdrc_rfr_ctrl_0_val @ fetch value from SRAM
ldr r11, omap3_sdrc_rfr_ctrl_0 @ fetch addr from SRAM
str r12, [r11] @ store
#ifdef CONFIG_OMAP3_SDRC_AC_TIMING
ldr r12, omap_sdrc_actim_ctrl_a_0_val
ldr r11, omap3_sdrc_actim_ctrl_a_0
str r12, [r11]
ldr r12, omap_sdrc_actim_ctrl_b_0_val
ldr r11, omap3_sdrc_actim_ctrl_b_0
str r12, [r11]
ldr r12, omap_sdrc_mr_0_val
ldr r11, omap3_sdrc_mr_0
str r12, [r11]
#endif
ldr r12, omap_sdrc_rfr_ctrl_1_val
cmp r12, #0 @ if SDRC_RFR_CTRL_1 is 0,
beq skip_cs1_prog @ do not program cs1 params
ldr r11, omap3_sdrc_rfr_ctrl_1
str r12, [r11]
#ifdef CONFIG_OMAP3_SDRC_AC_TIMING
ldr r12, omap_sdrc_actim_ctrl_a_1_val
ldr r11, omap3_sdrc_actim_ctrl_a_1
str r12, [r11]
ldr r12, omap_sdrc_actim_ctrl_b_1_val
ldr r11, omap3_sdrc_actim_ctrl_b_1
str r12, [r11]
ldr r12, omap_sdrc_mr_1_val
ldr r11, omap3_sdrc_mr_1
str r12, [r11]
#endif
skip_cs1_prog:
ldr r12, [r11] @ posted-write barrier for SDRC
bx lr
omap3_sdrc_power:
.word OMAP34XX_SDRC_REGADDR(SDRC_POWER)
omap3_cm_clksel1_pll:
.word OMAP34XX_CM_REGADDR(PLL_MOD, CM_CLKSEL1)
omap3_cm_idlest1_core:
.word OMAP34XX_CM_REGADDR(CORE_MOD, CM_IDLEST)
omap3_cm_iclken1_core:
.word OMAP34XX_CM_REGADDR(CORE_MOD, CM_ICLKEN1)
omap3_sdrc_rfr_ctrl_0:
.word OMAP34XX_SDRC_REGADDR(SDRC_RFR_CTRL_0)
omap3_sdrc_rfr_ctrl_1:
.word OMAP34XX_SDRC_REGADDR(SDRC_RFR_CTRL_1)
omap3_sdrc_actim_ctrl_a_0:
.word OMAP34XX_SDRC_REGADDR(SDRC_ACTIM_CTRL_A_0)
omap3_sdrc_actim_ctrl_a_1:
.word OMAP34XX_SDRC_REGADDR(SDRC_ACTIM_CTRL_A_1)
omap3_sdrc_actim_ctrl_b_0:
.word OMAP34XX_SDRC_REGADDR(SDRC_ACTIM_CTRL_B_0)
omap3_sdrc_actim_ctrl_b_1:
.word OMAP34XX_SDRC_REGADDR(SDRC_ACTIM_CTRL_B_1)
omap3_sdrc_mr_0:
.word OMAP34XX_SDRC_REGADDR(SDRC_MR_0)
omap3_sdrc_mr_1:
.word OMAP34XX_SDRC_REGADDR(SDRC_MR_1)
omap_sdrc_rfr_ctrl_0_val:
.word 0xDEADBEEF
omap_sdrc_rfr_ctrl_1_val:
.word 0xDEADBEEF
omap_sdrc_actim_ctrl_a_0_val:
.word 0xDEADBEEF
omap_sdrc_actim_ctrl_a_1_val:
.word 0xDEADBEEF
omap_sdrc_actim_ctrl_b_0_val:
.word 0xDEADBEEF
omap_sdrc_actim_ctrl_b_1_val:
.word 0xDEADBEEF
omap_sdrc_mr_0_val:
.word 0xDEADBEEF
omap_sdrc_mr_1_val:
.word 0xDEADBEEF
omap3_sdrc_dlla_status:
.word OMAP34XX_SDRC_REGADDR(SDRC_DLLA_STATUS)
omap3_sdrc_dlla_ctrl:
.word OMAP34XX_SDRC_REGADDR(SDRC_DLLA_CTRL)
core_m2_mask_val:
.word 0x07FFFFFF
ENTRY(omap3_sram_configure_core_dpll_sz)
.word . - omap3_sram_configure_core_dpll
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