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

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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>
This commit is contained in:
Grygorii Strashko 2013-03-16 11:46:47 +05:30 committed by Greg Kroah-Hartman
parent 36caf3e525
commit f02503b2ff
1 changed files with 35 additions and 0 deletions
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35
drivers/memory/emif.c
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@ -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);