diff options
| -rw-r--r-- | drivers/memory/emif.c | 35 |
1 files changed, 35 insertions, 0 deletions
diff --git a/drivers/memory/emif.c b/drivers/memory/emif.c index 9335339..bd223c7 100644 --- 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); |
