On Monday 11 March 2013 10:36 AM, Lokesh Vutla wrote:
> From: Grygorii Strashko <grygorii.strashko@xxxxxx>
>
> 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.
>
> Signed-off-by: Grygorii Strashko <grygorii.strashko@xxxxxx>
> Signed-off-by: Vitaly Chernooky <vitaly.chernooky@xxxxxx>
> Signed-off-by: Oleksandr Dmytryshyn <oleksandr.dmytryshyn@xxxxxx>
> Signed-off-by: Lokesh Vutla <lokeshvutla@xxxxxx>
> ---
Nice changelog.
> drivers/memory/emif.c | 35 +++++++++++++++++++++++++++++++++++
> 1 file changed, 35 insertions(+)
>
> diff --git a/drivers/memory/emif.c b/drivers/memory/emif.c
> index f75806a..119503a 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)) {
Ok. So the errata is limited to only 'EMIF_4D' version and not applicable
for next EMIF version used in OMAP5 devices, right ? If yes, would be good
to just mention that in already good changelog.
> + WARN_ONCE(1,
> + "REG_LP_MODE = LP_MODE_PWR_DN(4) is prohibited by"
> + "erratum i743 switch to LP_MODE_SELF_REFRESH(2)\n");
> + /* rallback LP_MODE to Self-refresh mode */
s/rallback/rollback ?
With above updates,
Acked-by: Santosh Shilimkar <santosh.shilimkar@xxxxxx>
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