memory: emif: errata i743: Prohibit usage of Power-Down mode

ERRATA DESCRIPTION :
The EMIF supports power-down state for low power. The EMIF
automatically puts the SDRAM into power-down after the memory is
not accessed for a defined number of cycles and the
EMIF_PWR_MGMT_CTRL[10:8] REG_LP_MODE bit field is set to 0x4.
As the EMIF supports automatic output impedance calibration, a ZQ
calibration long command is issued every time it exits active
power-down and precharge power-down modes. The EMIF waits and
blocks any other command during this calibration.
The EMIF does not allow selective disabling of ZQ calibration upon
exit of power-down mode. Due to very short periods of power-down
cycles, ZQ calibration overhead creates bandwidth issues and
increases overall system power consumption. On the other hand,
issuing ZQ calibration long commands when exiting self-refresh is
still required.

WORKAROUND :
Because there is no power consumption benefit of the power-down due
to the calibration and there is a performance risk, the guideline
is to not allow power-down state and, therefore, to not have set
the EMIF_PWR_MGMT_CTRL[10:8] REG_LP_MODE bit field to 0x4.

This is applicable only for EMIF4D IP used in OMAP4 Soc's.

Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Vitaly Chernooky <vitaly.chernooky@ti.com>
Signed-off-by: Oleksandr Dmytryshyn <oleksandr.dmytryshyn@ti.com>
Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/memory/emif.c b/drivers/memory/emif.c
index 9335339ebfdfea4e194e61d57dcb453857d2e7ee..bd223c7c3e7288b33b65a51990856c36cc16272e 100644 (file)
--- a/drivers/memory/emif.c
+++ b/drivers/memory/emif.c
@@ -257,6 +257,41 @@ static void set_lpmode(struct emif_data *emif, u8 lpmode)
        u32 temp;
        void __iomem *base = emif->base;
 
+       /*
+        * Workaround for errata i743 - LPDDR2 Power-Down State is Not
+        * Efficient
+        *
+        * i743 DESCRIPTION:
+        * The EMIF supports power-down state for low power. The EMIF
+        * automatically puts the SDRAM into power-down after the memory is
+        * not accessed for a defined number of cycles and the
+        * EMIF_PWR_MGMT_CTRL[10:8] REG_LP_MODE bit field is set to 0x4.
+        * As the EMIF supports automatic output impedance calibration, a ZQ
+        * calibration long command is issued every time it exits active
+        * power-down and precharge power-down modes. The EMIF waits and
+        * blocks any other command during this calibration.
+        * The EMIF does not allow selective disabling of ZQ calibration upon
+        * exit of power-down mode. Due to very short periods of power-down
+        * cycles, ZQ calibration overhead creates bandwidth issues and
+        * increases overall system power consumption. On the other hand,
+        * issuing ZQ calibration long commands when exiting self-refresh is
+        * still required.
+        *
+        * WORKAROUND
+        * Because there is no power consumption benefit of the power-down due
+        * to the calibration and there is a performance risk, the guideline
+        * is to not allow power-down state and, therefore, to not have set
+        * the EMIF_PWR_MGMT_CTRL[10:8] REG_LP_MODE bit field to 0x4.
+        */
+       if ((emif->plat_data->ip_rev == EMIF_4D) &&
+           (EMIF_LP_MODE_PWR_DN == lpmode)) {
+               WARN_ONCE(1,
+                         "REG_LP_MODE = LP_MODE_PWR_DN(4) is prohibited by"
+                         "erratum i743 switch to LP_MODE_SELF_REFRESH(2)\n");
+               /* rollback LP_MODE to Self-refresh mode */
+               lpmode = EMIF_LP_MODE_SELF_REFRESH;
+       }
+
        temp = readl(base + EMIF_POWER_MANAGEMENT_CONTROL);
        temp &= ~LP_MODE_MASK;
        temp |= (lpmode << LP_MODE_SHIFT);