linux-kernel - [PATCH 7/8] memory: emif: errata i743: Prohibit usage of Power-Down mode

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Date:	Mon, 11 Mar 2013 10:36:04 +0530
From:	Lokesh Vutla <lokeshvutla@...com>
To:	<linux-kernel@...r.kernel.org>, <santosh.shilimkar@...com>,
	<gregkh@...uxfoundation.org>
CC:	<linux-omap@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	Grygorii Strashko <grygorii.strashko@...com>,
	Vitaly Chernooky <vitaly.chernooky@...com>,
	Oleksandr Dmytryshyn <oleksandr.dmytryshyn@...com>,
	Lokesh Vutla <lokeshvutla@...com>
Subject: [PATCH 7/8] memory: emif: errata i743: Prohibit usage of Power-Down mode

From: Grygorii Strashko <grygorii.strashko@...com>

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@...com>
Signed-off-by: Vitaly Chernooky <vitaly.chernooky@...com>
Signed-off-by: Oleksandr Dmytryshyn <oleksandr.dmytryshyn@...com>
Signed-off-by: Lokesh Vutla <lokeshvutla@...com>
---
 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)) {
+		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 */
+		lpmode = EMIF_LP_MODE_SELF_REFRESH;
+	}
+
 	temp = readl(base + EMIF_POWER_MANAGEMENT_CONTROL);
 	temp &= ~LP_MODE_MASK;
 	temp |= (lpmode << LP_MODE_SHIFT);
-- 
1.7.9.5

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