mpc512x: Adjust the DRAM init sequence to the datasheet spec

Do maintain a 200 usecs period of stable power and clock before
asserting the CKE signal and sending commands, have at least 200
DRAM clock cycles pass after initialization before data access.

Signed-off-by: Anatolij Gustschin <agust@denx.de>

arch/powerpc/cpu/mpc512x/fixed_sdram.c

@@ -99,7 +99,19 @@ long int fixed_sdram(ddr512x_config_t *mddrc_config,
 	sync_law(&im->sysconf.ddrlaw.ar);
 
 	/* DDR Enable */
-	out_be32(&im->mddrc.ddr_sys_config, MDDRC_SYS_CFG_EN);
+	/*
+	 * the "enable" combination: DRAM controller out of reset,
+	 * clock enabled, command mode -- BUT leave CKE low for now
+	 */
+	i = MDDRC_SYS_CFG_EN & ~MDDRC_SYS_CFG_CKE_MASK;
+	out_be32(&im->mddrc.ddr_sys_config, i);
+	/* maintain 200 microseconds of stable power and clock */
+	udelay(200);
+	/* apply a NOP, it shouldn't harm */
+	out_be32(&im->mddrc.ddr_command, CONFIG_SYS_DDRCMD_NOP);
+	/* now assert CKE (high) */
+	i |= MDDRC_SYS_CFG_CKE_MASK;
+	out_be32(&im->mddrc.ddr_sys_config, i);
 
 	/* Initialize DDR Priority Manager */
 	out_be32(&im->mddrc.prioman_config1, CONFIG_SYS_MDDRCGRP_PM_CFG1);
@@ -148,6 +160,9 @@ long int fixed_sdram(ddr512x_config_t *mddrc_config,
 	out_be32(&im->mddrc.ddr_time_config0, mddrc_config->ddr_time_config0);
 	out_be32(&im->mddrc.ddr_sys_config, mddrc_config->ddr_sys_config);
 
+	/* Allow for the DLL to startup before accessing data */
+	udelay(10);
+
 	msize = get_ram_size(CONFIG_SYS_DDR_BASE, CONFIG_SYS_MAX_RAM_SIZE);
 	/* Fix DDR Local Window for new size */
 	out_be32(&im->sysconf.ddrlaw.ar, __ilog2(msize) - 1);

arch/powerpc/include/asm/immap_512x.h

@@ -351,6 +351,7 @@ typedef struct ddr512x {
 
 /* MDDRC SYS CFG and Timing CFG0 Registers */
 #define MDDRC_SYS_CFG_EN	0xF0000000
+#define MDDRC_SYS_CFG_CKE_MASK	0x40000000
 #define MDDRC_SYS_CFG_CMD_MASK	0x10000000
 #define MDDRC_REFRESH_ZERO_MASK	0x0000FFFF