2 files changed, 29 insertions, 2 deletions

diff --git a/arch/arm/mach-omap2/Kconfig b/arch/arm/mach-omap2/Kconfig
index 7309aab305a9..0cd25ceadb43 100644
--- a/arch/arm/mach-omap2/Kconfig
+++ b/arch/arm/mach-omap2/Kconfig
@@ -128,3 +128,15 @@ config OMAP3_EMU
         help
           Say Y here to enable debugging hardware of omap3
 
+config OMAP3_SDRC_AC_TIMING
+        bool "Enable SDRC AC timing register changes"
+        depends on ARCH_OMAP3 && ARCH_OMAP34XX
+        default n
+        help
+          If you know that none of your system initiators will attempt to
+          access SDRAM during CORE DVFS, select Y here.  This should boost
+          SDRAM performance at lower CORE OPPs.  There are relatively few
+          users who will wish to say yes at this point - almost everyone will
+          wish to say no.  Selecting yes without understanding what is
+          going on could result in system crashes;
+
diff --git a/arch/arm/mach-omap2/sram34xx.S b/arch/arm/mach-omap2/sram34xx.S
index 82aa4a3d160c..de99ba2a57ab 100644
--- a/arch/arm/mach-omap2/sram34xx.S
+++ b/arch/arm/mach-omap2/sram34xx.S
@@ -91,8 +91,19 @@
  *  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
+ * 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
@@ -219,6 +230,7 @@ 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]
@@ -228,11 +240,13 @@ configure_sdrc:
         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]
@@ -242,6 +256,7 @@ configure_sdrc:
         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