u-boot/arch/arm/mach-sunxi/dram_sun4i.c

// SPDX-License-Identifier: GPL-2.0+
/*
 * sunxi DRAM controller initialization
 * (C) Copyright 2012 Henrik Nordstrom <henrik@henriknordstrom.net>
 * (C) Copyright 2013 Luke Kenneth Casson Leighton <lkcl@lkcl.net>
 *
 * Based on sun4i Linux kernel sources mach-sunxi/pm/standby/dram*.c
 * and earlier U-Boot Allwinner A10 SPL work
 *
 * (C) Copyright 2007-2012
 * Allwinner Technology Co., Ltd. <www.allwinnertech.com>
 * Berg Xing <bergxing@allwinnertech.com>
 * Tom Cubie <tangliang@allwinnertech.com>
 */

/*
 * Unfortunately the only documentation we have on the sun7i DRAM
 * controller is Allwinner boot0 + boot1 code, and that code uses
 * magic numbers & shifts with no explanations. Hence this code is
 * rather undocumented and full of magic.
 */

#include <common.h>
#include <init.h>
#include <asm/io.h>
#include <asm/arch/clock.h>
#include <asm/arch/dram.h>
#include <asm/arch/timer.h>
#include <asm/arch/sys_proto.h>
#include <linux/delay.h>

#define CPU_CFG_CHIP_VER(n) ((n) << 6)
#define CPU_CFG_CHIP_VER_MASK CPU_CFG_CHIP_VER(0x3)
#define CPU_CFG_CHIP_REV_A 0x0
#define CPU_CFG_CHIP_REV_C1 0x1
#define CPU_CFG_CHIP_REV_C2 0x2
#define CPU_CFG_CHIP_REV_B 0x3

/*
 * Wait up to 1s for mask to be clear in given reg.
 */
static inline void await_bits_clear(u32 *reg, u32 mask)
{
	mctl_await_completion(reg, mask, 0);
}

/*
 * Wait up to 1s for mask to be set in given reg.
 */
static inline void await_bits_set(u32 *reg, u32 mask)
{
	mctl_await_completion(reg, mask, mask);
}

/*
 * This performs the external DRAM reset by driving the RESET pin low and
 * then high again. According to the DDR3 spec, the RESET pin needs to be
 * kept low for at least 200 us.
 */
static void mctl_ddr3_reset(void)
{
	struct sunxi_dram_reg *dram =
			(struct sunxi_dram_reg *)SUNXI_DRAMC_BASE;

#ifdef CONFIG_MACH_SUN4I
	struct sunxi_timer_reg *timer =
			(struct sunxi_timer_reg *)SUNXI_TIMER_BASE;
	u32 reg_val;

	writel(0, &timer->cpu_cfg);
	reg_val = readl(&timer->cpu_cfg);

	if ((reg_val & CPU_CFG_CHIP_VER_MASK) !=
	    CPU_CFG_CHIP_VER(CPU_CFG_CHIP_REV_A)) {
		setbits_le32(&dram->mcr, DRAM_MCR_RESET);
		udelay(200);
		clrbits_le32(&dram->mcr, DRAM_MCR_RESET);
	} else
#endif
	{
		clrbits_le32(&dram->mcr, DRAM_MCR_RESET);
		udelay(200);
		setbits_le32(&dram->mcr, DRAM_MCR_RESET);
	}
	/* After the RESET pin is de-asserted, the DDR3 spec requires to wait
	 * for additional 500 us before driving the CKE pin (Clock Enable)
	 * high. The duration of this delay can be configured in the SDR_IDCR
	 * (Initialization Delay Configuration Register) and applied
	 * automatically by the DRAM controller during the DDR3 initialization
	 * step. But SDR_IDCR has limited range on sun4i/sun5i hardware and
	 * can't provide sufficient delay at DRAM clock frequencies higher than
	 * 524 MHz (while Allwinner A13 supports DRAM clock frequency up to
	 * 533 MHz according to the datasheet). Additionally, there is no
	 * official documentation for the SDR_IDCR register anywhere, and
	 * there is always a chance that we are interpreting it wrong.
	 * Better be safe than sorry, so add an explicit delay here. */
	udelay(500);
}

static void mctl_set_drive(void)
{
	struct sunxi_dram_reg *dram = (struct sunxi_dram_reg *)SUNXI_DRAMC_BASE;

#ifdef CONFIG_MACH_SUN7I
	clrsetbits_le32(&dram->mcr, DRAM_MCR_MODE_NORM(0x3) | (0x3 << 28),
#else
	clrsetbits_le32(&dram->mcr, DRAM_MCR_MODE_NORM(0x3),
#endif
			DRAM_MCR_MODE_EN(0x3) |
			0xffc);
}

static void mctl_itm_disable(void)
{
	struct sunxi_dram_reg *dram = (struct sunxi_dram_reg *)SUNXI_DRAMC_BASE;

	clrsetbits_le32(&dram->ccr, DRAM_CCR_INIT, DRAM_CCR_ITM_OFF);
}

static void mctl_itm_enable(void)
{
	struct sunxi_dram_reg *dram = (struct sunxi_dram_reg *)SUNXI_DRAMC_BASE;

	clrbits_le32(&dram->ccr, DRAM_CCR_ITM_OFF);
}

static void mctl_itm_reset(void)
{
	mctl_itm_disable();
	udelay(1); /* ITM reset needs a bit of delay */
	mctl_itm_enable();
	udelay(1);
}

static void mctl_enable_dll0(u32 phase)
{
	struct sunxi_dram_reg *dram = (struct sunxi_dram_reg *)SUNXI_DRAMC_BASE;

	clrsetbits_le32(&dram->dllcr[0], 0x3f << 6,
			((phase >> 16) & 0x3f) << 6);
	clrsetbits_le32(&dram->dllcr[0], DRAM_DLLCR_NRESET, DRAM_DLLCR_DISABLE);
	udelay(2);

	clrbits_le32(&dram->dllcr[0], DRAM_DLLCR_NRESET | DRAM_DLLCR_DISABLE);
	udelay(22);

	clrsetbits_le32(&dram->dllcr[0], DRAM_DLLCR_DISABLE, DRAM_DLLCR_NRESET);
	udelay(22);
}

/* Get the number of DDR byte lanes */
static u32 mctl_get_number_of_lanes(void)
{
	struct sunxi_dram_reg *dram = (struct sunxi_dram_reg *)SUNXI_DRAMC_BASE;
	if ((readl(&dram->dcr) & DRAM_DCR_BUS_WIDTH_MASK) ==
				DRAM_DCR_BUS_WIDTH(DRAM_DCR_BUS_WIDTH_32BIT))
		return 4;
	else
		return 2;
}

/*
 * Note: This differs from pm/standby in that it checks the bus width
 */
static void mctl_enable_dllx(u32 phase)
{
	struct sunxi_dram_reg *dram = (struct sunxi_dram_reg *)SUNXI_DRAMC_BASE;
	u32 i, number_of_lanes;

	number_of_lanes = mctl_get_number_of_lanes();

	for (i = 1; i <= number_of_lanes; i++) {
		clrsetbits_le32(&dram->dllcr[i], 0xf << 14,
				(phase & 0xf) << 14);
		clrsetbits_le32(&dram->dllcr[i], DRAM_DLLCR_NRESET,
				DRAM_DLLCR_DISABLE);
		phase >>= 4;
	}
	udelay(2);

	for (i = 1; i <= number_of_lanes; i++)
		clrbits_le32(&dram->dllcr[i], DRAM_DLLCR_NRESET |
			     DRAM_DLLCR_DISABLE);
	udelay(22);

	for (i = 1; i <= number_of_lanes; i++)
		clrsetbits_le32(&dram->dllcr[i], DRAM_DLLCR_DISABLE,
				DRAM_DLLCR_NRESET);
	udelay(22);
}

static u32 hpcr_value[32] = {
#ifdef CONFIG_MACH_SUN5I
	0, 0, 0, 0,
	0, 0, 0, 0,
	0, 0, 0, 0,
	0, 0, 0, 0,
	0x1031, 0x1031, 0x0735, 0x1035,
	0x1035, 0x0731, 0x1031, 0,
	0x0301, 0x0301, 0x0301, 0x0301,
	0x0301, 0x0301, 0x0301, 0
#endif
#ifdef CONFIG_MACH_SUN4I
	0x0301, 0x0301, 0x0301, 0x0301,
	0x0301, 0x0301, 0, 0,
	0, 0, 0, 0,
	0, 0, 0, 0,
	0x1031, 0x1031, 0x0735, 0x5031,
	0x1035, 0x0731, 0x1031, 0x0735,
	0x1035, 0x1031, 0x0731, 0x1035,
	0x1031, 0x0301, 0x0301, 0x0731
#endif
#ifdef CONFIG_MACH_SUN7I
	0x0301, 0x0301, 0x0301, 0x0301,
	0x0301, 0x0301, 0x0301, 0x0301,
	0, 0, 0, 0,
	0, 0, 0, 0,
	0x1031, 0x1031, 0x0735, 0x1035,
	0x1035, 0x0731, 0x1031, 0x0735,
	0x1035, 0x1031, 0x0731, 0x1035,
	0x0001, 0x1031, 0, 0x1031
	/* last row differs from boot0 source table
	 * 0x1031, 0x0301, 0x0301, 0x0731
	 * but boot0 code skips #28 and #30, and sets #29 and #31 to the
	 * value from #28 entry (0x1031)
	 */
#endif
};

static void mctl_configure_hostport(void)
{
	struct sunxi_dram_reg *dram = (struct sunxi_dram_reg *)SUNXI_DRAMC_BASE;
	u32 i;

	for (i = 0; i < 32; i++)
		writel(hpcr_value[i], &dram->hpcr[i]);
}

static void mctl_setup_dram_clock(u32 clk, u32 mbus_clk)
{
	u32 reg_val;
	struct sunxi_ccm_reg *ccm = (struct sunxi_ccm_reg *)SUNXI_CCM_BASE;
	u32 pll5p_clk, pll6x_clk;
	u32 pll5p_div, pll6x_div;
	u32 pll5p_rate, pll6x_rate;

	/* setup DRAM PLL */
	reg_val = readl(&ccm->pll5_cfg);
	reg_val &= ~CCM_PLL5_CTRL_M_MASK;		/* set M to 0 (x1) */
	reg_val &= ~CCM_PLL5_CTRL_K_MASK;		/* set K to 0 (x1) */
	reg_val &= ~CCM_PLL5_CTRL_N_MASK;		/* set N to 0 (x0) */
	reg_val &= ~CCM_PLL5_CTRL_P_MASK;		/* set P to 0 (x1) */
#ifdef CONFIG_OLD_SUNXI_KERNEL_COMPAT
	/* Old kernels are hardcoded to P=1 (divide by 2) */
	reg_val |= CCM_PLL5_CTRL_P(1);
#endif
	if (clk >= 540 && clk < 552) {
		/* dram = 540MHz */
		reg_val |= CCM_PLL5_CTRL_M(CCM_PLL5_CTRL_M_X(2));
		reg_val |= CCM_PLL5_CTRL_K(CCM_PLL5_CTRL_K_X(3));
		reg_val |= CCM_PLL5_CTRL_N(CCM_PLL5_CTRL_N_X(15));
	} else if (clk >= 512 && clk < 528) {
		/* dram = 512MHz */
		reg_val |= CCM_PLL5_CTRL_M(CCM_PLL5_CTRL_M_X(3));
		reg_val |= CCM_PLL5_CTRL_K(CCM_PLL5_CTRL_K_X(4));
		reg_val |= CCM_PLL5_CTRL_N(CCM_PLL5_CTRL_N_X(16));
	} else if (clk >= 496 && clk < 504) {
		/* dram = 496MHz */
		reg_val |= CCM_PLL5_CTRL_M(CCM_PLL5_CTRL_M_X(3));
		reg_val |= CCM_PLL5_CTRL_K(CCM_PLL5_CTRL_K_X(2));
		reg_val |= CCM_PLL5_CTRL_N(CCM_PLL5_CTRL_N_X(31));
	} else if (clk >= 468 && clk < 480) {
		/* dram = 468MHz */
		reg_val |= CCM_PLL5_CTRL_M(CCM_PLL5_CTRL_M_X(2));
		reg_val |= CCM_PLL5_CTRL_K(CCM_PLL5_CTRL_K_X(3));
		reg_val |= CCM_PLL5_CTRL_N(CCM_PLL5_CTRL_N_X(13));
	} else if (clk >= 396 && clk < 408) {
		/* dram = 396MHz */
		reg_val |= CCM_PLL5_CTRL_M(CCM_PLL5_CTRL_M_X(2));
		reg_val |= CCM_PLL5_CTRL_K(CCM_PLL5_CTRL_K_X(3));
		reg_val |= CCM_PLL5_CTRL_N(CCM_PLL5_CTRL_N_X(11));
	} else {
		/* any other frequency that is a multiple of 24 */
		reg_val |= CCM_PLL5_CTRL_M(CCM_PLL5_CTRL_M_X(2));
		reg_val |= CCM_PLL5_CTRL_K(CCM_PLL5_CTRL_K_X(2));
		reg_val |= CCM_PLL5_CTRL_N(CCM_PLL5_CTRL_N_X(clk / 24));
	}
	reg_val &= ~CCM_PLL5_CTRL_VCO_GAIN;		/* PLL VCO Gain off */
	reg_val |= CCM_PLL5_CTRL_EN;			/* PLL On */
	writel(reg_val, &ccm->pll5_cfg);
	udelay(5500);

	setbits_le32(&ccm->pll5_cfg, CCM_PLL5_CTRL_DDR_CLK);

#if defined(CONFIG_MACH_SUN4I) || defined(CONFIG_MACH_SUN7I)
	/* reset GPS */
	clrbits_le32(&ccm->gps_clk_cfg, CCM_GPS_CTRL_RESET | CCM_GPS_CTRL_GATE);
	setbits_le32(&ccm->ahb_gate0, CCM_AHB_GATE_GPS);
	udelay(1);
	clrbits_le32(&ccm->ahb_gate0, CCM_AHB_GATE_GPS);
#endif

	/* setup MBUS clock */
	if (!mbus_clk)
		mbus_clk = 300;

	/* PLL5P and PLL6 are the potential clock sources for MBUS */
	pll6x_clk = clock_get_pll6() / 1000000;
#ifdef CONFIG_MACH_SUN7I
	pll6x_clk *= 2; /* sun7i uses PLL6*2, sun5i uses just PLL6 */
#endif
	pll5p_clk = clock_get_pll5p() / 1000000;
	pll6x_div = DIV_ROUND_UP(pll6x_clk, mbus_clk);
	pll5p_div = DIV_ROUND_UP(pll5p_clk, mbus_clk);
	pll6x_rate = pll6x_clk / pll6x_div;
	pll5p_rate = pll5p_clk / pll5p_div;

	if (pll6x_div <= 16 && pll6x_rate > pll5p_rate) {
		/* use PLL6 as the MBUS clock source */
		reg_val = CCM_MBUS_CTRL_GATE |
			  CCM_MBUS_CTRL_CLK_SRC(CCM_MBUS_CTRL_CLK_SRC_PLL6) |
			  CCM_MBUS_CTRL_N(CCM_MBUS_CTRL_N_X(1)) |
			  CCM_MBUS_CTRL_M(CCM_MBUS_CTRL_M_X(pll6x_div));
	} else if (pll5p_div <= 16) {
		/* use PLL5P as the MBUS clock source */
		reg_val = CCM_MBUS_CTRL_GATE |
			  CCM_MBUS_CTRL_CLK_SRC(CCM_MBUS_CTRL_CLK_SRC_PLL5) |
			  CCM_MBUS_CTRL_N(CCM_MBUS_CTRL_N_X(1)) |
			  CCM_MBUS_CTRL_M(CCM_MBUS_CTRL_M_X(pll5p_div));
	} else {
		panic("Bad mbus_clk\n");
	}
	writel(reg_val, &ccm->mbus_clk_cfg);

	/*
	 * open DRAMC AHB & DLL register clock
	 * close it first
	 */
#if defined(CONFIG_MACH_SUN5I) || defined(CONFIG_MACH_SUN7I)
	clrbits_le32(&ccm->ahb_gate0, CCM_AHB_GATE_SDRAM | CCM_AHB_GATE_DLL);
#else
	clrbits_le32(&ccm->ahb_gate0, CCM_AHB_GATE_SDRAM);
#endif
	udelay(22);

	/* then open it */
#if defined(CONFIG_MACH_SUN5I) || defined(CONFIG_MACH_SUN7I)
	setbits_le32(&ccm->ahb_gate0, CCM_AHB_GATE_SDRAM | CCM_AHB_GATE_DLL);
#else
	setbits_le32(&ccm->ahb_gate0, CCM_AHB_GATE_SDRAM);
#endif
	udelay(22);
}

/*
 * The data from rslrX and rdgrX registers (X=rank) is stored
 * in a single 32-bit value using the following format:
 *   bits [31:26] - DQS gating system latency for byte lane 3
 *   bits [25:24] - DQS gating phase select for byte lane 3
 *   bits [23:18] - DQS gating system latency for byte lane 2
 *   bits [17:16] - DQS gating phase select for byte lane 2
 *   bits [15:10] - DQS gating system latency for byte lane 1
 *   bits [ 9:8 ] - DQS gating phase select for byte lane 1
 *   bits [ 7:2 ] - DQS gating system latency for byte lane 0
 *   bits [ 1:0 ] - DQS gating phase select for byte lane 0
 */
static void mctl_set_dqs_gating_delay(int rank, u32 dqs_gating_delay)
{
	struct sunxi_dram_reg *dram = (struct sunxi_dram_reg *)SUNXI_DRAMC_BASE;
	u32 lane, number_of_lanes = mctl_get_number_of_lanes();
	/* rank0 gating system latency (3 bits per lane: cycles) */
	u32 slr = readl(rank == 0 ? &dram->rslr0 : &dram->rslr1);
	/* rank0 gating phase select (2 bits per lane: 90, 180, 270, 360) */
	u32 dgr = readl(rank == 0 ? &dram->rdgr0 : &dram->rdgr1);
	for (lane = 0; lane < number_of_lanes; lane++) {
		u32 tmp = dqs_gating_delay >> (lane * 8);
		slr &= ~(7 << (lane * 3));
		slr |= ((tmp >> 2) & 7) << (lane * 3);
		dgr &= ~(3 << (lane * 2));
		dgr |= (tmp & 3) << (lane * 2);
	}
	writel(slr, rank == 0 ? &dram->rslr0 : &dram->rslr1);
	writel(dgr, rank == 0 ? &dram->rdgr0 : &dram->rdgr1);
}

static int dramc_scan_readpipe(void)
{
	struct sunxi_dram_reg *dram = (struct sunxi_dram_reg *)SUNXI_DRAMC_BASE;
	u32 reg_val;

	/* data training trigger */
	clrbits_le32(&dram->csr, DRAM_CSR_FAILED);
	setbits_le32(&dram->ccr, DRAM_CCR_DATA_TRAINING);

	/* check whether data training process has completed */
	await_bits_clear(&dram->ccr, DRAM_CCR_DATA_TRAINING);

	/* check data training result */
	reg_val = readl(&dram->csr);
	if (reg_val & DRAM_CSR_FAILED)
		return -1;

	return 0;
}

static void dramc_clock_output_en(u32 on)
{
#if defined(CONFIG_MACH_SUN5I) || defined(CONFIG_MACH_SUN7I)
	struct sunxi_dram_reg *dram = (struct sunxi_dram_reg *)SUNXI_DRAMC_BASE;

	if (on)
		setbits_le32(&dram->mcr, DRAM_MCR_DCLK_OUT);
	else
		clrbits_le32(&dram->mcr, DRAM_MCR_DCLK_OUT);
#endif
#ifdef CONFIG_MACH_SUN4I
	struct sunxi_ccm_reg *ccm = (struct sunxi_ccm_reg *)SUNXI_CCM_BASE;
	if (on)
		setbits_le32(&ccm->dram_clk_gate, CCM_DRAM_CTRL_DCLK_OUT);
	else
		clrbits_le32(&ccm->dram_clk_gate, CCM_DRAM_CTRL_DCLK_OUT);
#endif
}

/* tRFC in nanoseconds for different densities (from the DDR3 spec) */
static const u16 tRFC_DDR3_table[6] = {
	/* 256Mb    512Mb    1Gb      2Gb      4Gb      8Gb */
	   90,      90,      110,     160,     300,     350
};

static void dramc_set_autorefresh_cycle(u32 clk, u32 density)
{
	struct sunxi_dram_reg *dram = (struct sunxi_dram_reg *)SUNXI_DRAMC_BASE;
	u32 tRFC, tREFI;

	tRFC = (tRFC_DDR3_table[density] * clk + 999) / 1000;
	tREFI = (7987 * clk) >> 10;	/* <= 7.8us */

	writel(DRAM_DRR_TREFI(tREFI) | DRAM_DRR_TRFC(tRFC), &dram->drr);
}

/* Calculate the value for A11, A10, A9 bits in MR0 (write recovery) */
static u32 ddr3_write_recovery(u32 clk)
{
	u32 twr_ns = 15; /* DDR3 spec says that it is 15ns for all speed bins */
	u32 twr_ck = (twr_ns * clk + 999) / 1000;
	if (twr_ck < 5)
		return 1;
	else if (twr_ck <= 8)
		return twr_ck - 4;
	else if (twr_ck <= 10)
		return 5;
	else
		return 6;
}

/*
 * If the dram->ppwrsctl (SDR_DPCR) register has the lowest bit set to 1, this
 * means that DRAM is currently in self-refresh mode and retaining the old
 * data. Since we have no idea what to do in this situation yet, just set this
 * register to 0 and initialize DRAM in the same way as on any normal reboot
 * (discarding whatever was stored there).
 *
 * Note: on sun7i hardware, the highest 16 bits need to be set to 0x1651 magic
 * value for this write operation to have any effect. On sun5i hadware this
 * magic value is not necessary. And on sun4i hardware the writes to this
 * register seem to have no effect at all.
 */
static void mctl_disable_power_save(void)
{
	struct sunxi_dram_reg *dram = (struct sunxi_dram_reg *)SUNXI_DRAMC_BASE;
	writel(0x16510000, &dram->ppwrsctl);
}

/*
 * After the DRAM is powered up or reset, the DDR3 spec requires to wait at
 * least 500 us before driving the CKE pin (Clock Enable) high. The dram->idct
 * (SDR_IDCR) register appears to configure this delay, which gets applied
 * right at the time when the DRAM initialization is activated in the
 * 'mctl_ddr3_initialize' function.
 */
static void mctl_set_cke_delay(void)
{
	struct sunxi_dram_reg *dram = (struct sunxi_dram_reg *)SUNXI_DRAMC_BASE;

	/* The CKE delay is represented in DRAM clock cycles, multiplied by N
	 * (where N=2 for sun4i/sun5i and N=3 for sun7i). Here it is set to
	 * the maximum possible value 0x1ffff, just like in the Allwinner's
	 * boot0 bootloader. The resulting delay value is somewhere between
	 * ~0.4 ms (sun5i with 648 MHz DRAM clock speed) and ~1.1 ms (sun7i
	 * with 360 MHz DRAM clock speed). */
	setbits_le32(&dram->idcr, 0x1ffff);
}

/*
 * This triggers the DRAM initialization. It performs sending the mode registers
 * to the DRAM among other things. Very likely the ZQCL command is also getting
 * executed (to do the initial impedance calibration on the DRAM side of the
 * wire). The memory controller and the PHY must be already configured before
 * calling this function.
 */
static void mctl_ddr3_initialize(void)
{
	struct sunxi_dram_reg *dram = (struct sunxi_dram_reg *)SUNXI_DRAMC_BASE;
	setbits_le32(&dram->ccr, DRAM_CCR_INIT);
	await_bits_clear(&dram->ccr, DRAM_CCR_INIT);
}

/*
 * Perform impedance calibration on the DRAM controller side of the wire.
 */
static void mctl_set_impedance(u32 zq, bool odt_en)
{
	struct sunxi_dram_reg *dram = (struct sunxi_dram_reg *)SUNXI_DRAMC_BASE;
	u32 reg_val;
	u32 zprog = zq & 0xFF, zdata = (zq >> 8) & 0xFFFFF;

#ifndef CONFIG_MACH_SUN7I
	/* Appears that some kind of automatically initiated default
	 * ZQ calibration is already in progress at this point on sun4i/sun5i
	 * hardware, but not on sun7i. So it is reasonable to wait for its
	 * completion before doing anything else. */
	await_bits_set(&dram->zqsr, DRAM_ZQSR_ZDONE);
#endif

	/* ZQ calibration is not really useful unless ODT is enabled */
	if (!odt_en)
		return;

#ifdef CONFIG_MACH_SUN7I
	/* Enabling ODT in SDR_IOCR on sun7i hardware results in a deadlock
	 * unless bit 24 is set in SDR_ZQCR1. Not much is known about the
	 * SDR_ZQCR1 register, but there are hints indicating that it might
	 * be related to periodic impedance re-calibration. This particular
	 * magic value is borrowed from the Allwinner boot0 bootloader, and
	 * using it helps to avoid troubles */
	writel((1 << 24) | (1 << 1), &dram->zqcr1);
#endif

	/* Needed at least for sun5i, because it does not self clear there */
	clrbits_le32(&dram->zqcr0, DRAM_ZQCR0_ZCAL);

	if (zdata) {
		/* Set the user supplied impedance data */
		reg_val = DRAM_ZQCR0_ZDEN | zdata;
		writel(reg_val, &dram->zqcr0);
		/* no need to wait, this takes effect immediately */
	} else {
		/* Do the calibration using the external resistor */
		reg_val = DRAM_ZQCR0_ZCAL | DRAM_ZQCR0_IMP_DIV(zprog);
		writel(reg_val, &dram->zqcr0);
		/* Wait for the new impedance configuration to settle */
		await_bits_set(&dram->zqsr, DRAM_ZQSR_ZDONE);
	}

	/* Needed at least for sun5i, because it does not self clear there */
	clrbits_le32(&dram->zqcr0, DRAM_ZQCR0_ZCAL);

	/* Set I/O configure register */
	writel(DRAM_IOCR_ODT_EN, &dram->iocr);
}

static unsigned long dramc_init_helper(struct dram_para *para)
{
	struct sunxi_dram_reg *dram = (struct sunxi_dram_reg *)SUNXI_DRAMC_BASE;
	u32 reg_val;
	u32 density;
	int ret_val;

	/*
	 * only single rank DDR3 is supported by this code even though the
	 * hardware can theoretically support DDR2 and up to two ranks
	 */
	if (para->type != DRAM_MEMORY_TYPE_DDR3 || para->rank_num != 1)
		return 0;

	/* setup DRAM relative clock */
	mctl_setup_dram_clock(para->clock, para->mbus_clock);

	/* Disable any pad power save control */
	mctl_disable_power_save();

	mctl_set_drive();

	/* dram clock off */
	dramc_clock_output_en(0);

#ifdef CONFIG_MACH_SUN4I
	/* select dram controller 1 */
	writel(DRAM_CSEL_MAGIC, &dram->csel);
#endif

	mctl_itm_disable();
	mctl_enable_dll0(para->tpr3);

	/* configure external DRAM */
	reg_val = DRAM_DCR_TYPE_DDR3;
	reg_val |= DRAM_DCR_IO_WIDTH(para->io_width >> 3);

	if (para->density == 256)
		density = DRAM_DCR_CHIP_DENSITY_256M;
	else if (para->density == 512)
		density = DRAM_DCR_CHIP_DENSITY_512M;
	else if (para->density == 1024)
		density = DRAM_DCR_CHIP_DENSITY_1024M;
	else if (para->density == 2048)
		density = DRAM_DCR_CHIP_DENSITY_2048M;
	else if (para->density == 4096)
		density = DRAM_DCR_CHIP_DENSITY_4096M;
	else if (para->density == 8192)
		density = DRAM_DCR_CHIP_DENSITY_8192M;
	else
		density = DRAM_DCR_CHIP_DENSITY_256M;

	reg_val |= DRAM_DCR_CHIP_DENSITY(density);
	reg_val |= DRAM_DCR_BUS_WIDTH((para->bus_width >> 3) - 1);
	reg_val |= DRAM_DCR_RANK_SEL(para->rank_num - 1);
	reg_val |= DRAM_DCR_CMD_RANK_ALL;
	reg_val |= DRAM_DCR_MODE(DRAM_DCR_MODE_INTERLEAVE);
	writel(reg_val, &dram->dcr);

	dramc_clock_output_en(1);

	mctl_set_impedance(para->zq, para->odt_en);

	mctl_set_cke_delay();

	mctl_ddr3_reset();

	udelay(1);

	await_bits_clear(&dram->ccr, DRAM_CCR_INIT);

	mctl_enable_dllx(para->tpr3);

	/* set refresh period */
	dramc_set_autorefresh_cycle(para->clock, density);

	/* set timing parameters */
	writel(para->tpr0, &dram->tpr0);
	writel(para->tpr1, &dram->tpr1);
	writel(para->tpr2, &dram->tpr2);

	reg_val = DRAM_MR_BURST_LENGTH(0x0);
#if (defined(CONFIG_MACH_SUN5I) || defined(CONFIG_MACH_SUN7I))
	reg_val |= DRAM_MR_POWER_DOWN;
#endif
	reg_val |= DRAM_MR_CAS_LAT(para->cas - 4);
	reg_val |= DRAM_MR_WRITE_RECOVERY(ddr3_write_recovery(para->clock));
	writel(reg_val, &dram->mr);

	writel(para->emr1, &dram->emr);
	writel(para->emr2, &dram->emr2);
	writel(para->emr3, &dram->emr3);

	/* disable drift compensation and set passive DQS window mode */
	clrsetbits_le32(&dram->ccr, DRAM_CCR_DQS_DRIFT_COMP, DRAM_CCR_DQS_GATE);

#ifdef CONFIG_MACH_SUN7I
	/* Command rate timing mode 2T & 1T */
	if (para->tpr4 & 0x1)
		setbits_le32(&dram->ccr, DRAM_CCR_COMMAND_RATE_1T);
#endif
	/* initialize external DRAM */
	mctl_ddr3_initialize();

	/* scan read pipe value */
	mctl_itm_enable();

	/* Hardware DQS gate training */
	ret_val = dramc_scan_readpipe();

	if (ret_val < 0)
		return 0;

	/* allow to override the DQS training results with a custom delay */
	if (para->dqs_gating_delay)
		mctl_set_dqs_gating_delay(0, para->dqs_gating_delay);

	/* set the DQS gating window type */
	if (para->active_windowing)
		clrbits_le32(&dram->ccr, DRAM_CCR_DQS_GATE);
	else
		setbits_le32(&dram->ccr, DRAM_CCR_DQS_GATE);

	mctl_itm_reset();

	/* configure all host port */
	mctl_configure_hostport();

	return get_ram_size((long *)PHYS_SDRAM_0, PHYS_SDRAM_0_SIZE);
}

unsigned long dramc_init(struct dram_para *para)
{
	unsigned long dram_size, actual_density;

	/* If the dram configuration is not provided, use a default */
	if (!para)
		return 0;

	/* if everything is known, then autodetection is not necessary */
	if (para->io_width && para->bus_width && para->density)
		return dramc_init_helper(para);

	/* try to autodetect the DRAM bus width and density */
	para->io_width  = 16;
	para->bus_width = 32;
#if defined(CONFIG_MACH_SUN4I) || defined(CONFIG_MACH_SUN5I)
	/* only A0-A14 address lines on A10/A13, limiting max density to 4096 */
	para->density = 4096;
#else
	/* all A0-A15 address lines on A20, which allow density 8192 */
	para->density = 8192;
#endif

	dram_size = dramc_init_helper(para);
	if (!dram_size) {
		/* if 32-bit bus width failed, try 16-bit bus width instead */
		para->bus_width = 16;
		dram_size = dramc_init_helper(para);
		if (!dram_size) {
			/* if 16-bit bus width also failed, then bail out */
			return dram_size;
		}
	}

	/* check if we need to adjust the density */
	actual_density = (dram_size >> 17) * para->io_width / para->bus_width;

	if (actual_density != para->density) {
		/* update the density and re-initialize DRAM again */
		para->density = actual_density;
		dram_size = dramc_init_helper(para);
	}

	return dram_size;
}