cpu/mpc8xxx/ddr/lc_common_dimm_params.c - u-boot - Git at Google

 /*
  * Copyright 2008 Freescale Semiconductor, Inc.
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License
  * Version 2 as published by the Free Software Foundation.
  */

 #include <common.h>
 #include <asm/fsl_ddr_sdram.h>

 #include "ddr.h"

 /*
  * compute_lowest_common_dimm_parameters()
  *
  * Determine the worst-case DIMM timing parameters from the set of DIMMs
  * whose parameters have been computed into the array pointed to
  * by dimm_params.
  */
 unsigned int
 compute_lowest_common_dimm_parameters(const dimm_params_t *dimm_params,
 				      common_timing_params_t *outpdimm,
 				      unsigned int number_of_dimms)
 {
 	unsigned int i;

 	unsigned int tCKmin_X_ps = 0;
 	unsigned int tCKmax_ps = 0xFFFFFFFF;
 	unsigned int tCKmax_max_ps = 0;
 	unsigned int tRCD_ps = 0;
 	unsigned int tRP_ps = 0;
 	unsigned int tRAS_ps = 0;
 	unsigned int tWR_ps = 0;
 	unsigned int tWTR_ps = 0;
 	unsigned int tRFC_ps = 0;
 	unsigned int tRRD_ps = 0;
 	unsigned int tRC_ps = 0;
 	unsigned int refresh_rate_ps = 0;
 	unsigned int tIS_ps = 0;
 	unsigned int tIH_ps = 0;
 	unsigned int tDS_ps = 0;
 	unsigned int tDH_ps = 0;
 	unsigned int tRTP_ps = 0;
 	unsigned int tDQSQ_max_ps = 0;
 	unsigned int tQHS_ps = 0;

 	unsigned int temp1, temp2;
 	unsigned int lowest_good_caslat;
 	unsigned int additive_latency = 0;
 	const unsigned int mclk_ps = get_memory_clk_period_ps();
 	unsigned int not_ok;

 	debug("using mclk_ps = %u\n", mclk_ps);

 	temp1 = 0;
 	for (i = 0; i < number_of_dimms; i++) {
 		/*
 		 * If there are no ranks on this DIMM,
 		 * it probably doesn't exist, so skip it.
 		 */
 		if (dimm_params[i].n_ranks == 0) {
 			temp1++;
 			continue;
 		}

 		/*
 		 * Find minimum tCKmax_ps to find fastest slow speed,
 		 * i.e., this is the slowest the whole system can go.
 		 */
 		tCKmax_ps = min(tCKmax_ps, dimm_params[i].tCKmax_ps);

 		/* Either find maximum value to determine slowest
 		 * speed, delay, time, period, etc */
 		tCKmin_X_ps = max(tCKmin_X_ps, dimm_params[i].tCKmin_X_ps);
 		tCKmax_max_ps = max(tCKmax_max_ps, dimm_params[i].tCKmax_ps);
 		tRCD_ps = max(tRCD_ps, dimm_params[i].tRCD_ps);
 		tRP_ps = max(tRP_ps, dimm_params[i].tRP_ps);
 		tRAS_ps = max(tRAS_ps, dimm_params[i].tRAS_ps);
 		tWR_ps = max(tWR_ps, dimm_params[i].tWR_ps);
 		tWTR_ps = max(tWTR_ps, dimm_params[i].tWTR_ps);
 		tRFC_ps = max(tRFC_ps, dimm_params[i].tRFC_ps);
 		tRRD_ps = max(tRRD_ps, dimm_params[i].tRRD_ps);
 		tRC_ps = max(tRC_ps, dimm_params[i].tRC_ps);
 		tIS_ps = max(tIS_ps, dimm_params[i].tIS_ps);
 		tIH_ps = max(tIH_ps, dimm_params[i].tIH_ps);
 		tDS_ps = max(tDS_ps, dimm_params[i].tDS_ps);
 		tDH_ps = max(tDH_ps, dimm_params[i].tDH_ps);
 		tRTP_ps = max(tRTP_ps, dimm_params[i].tRTP_ps);
 		tQHS_ps = max(tQHS_ps, dimm_params[i].tQHS_ps);
 		refresh_rate_ps = max(refresh_rate_ps,
 				      dimm_params[i].refresh_rate_ps);

 		/*
 		 * Find maximum tDQSQ_max_ps to find slowest.
 		 *
 		 * FIXME: is finding the slowest value the correct
 		 * strategy for this parameter?
 		 */
 		tDQSQ_max_ps = max(tDQSQ_max_ps, dimm_params[i].tDQSQ_max_ps);
 	}

 	outpdimm->ndimms_present = number_of_dimms - temp1;

 	if (temp1 == number_of_dimms) {
 		debug("no dimms this memory controller\n");
 		return 0;
 	}

 	outpdimm->tCKmin_X_ps = tCKmin_X_ps;
 	outpdimm->tCKmax_ps = tCKmax_ps;
 	outpdimm->tCKmax_max_ps = tCKmax_max_ps;
 	outpdimm->tRCD_ps = tRCD_ps;
 	outpdimm->tRP_ps = tRP_ps;
 	outpdimm->tRAS_ps = tRAS_ps;
 	outpdimm->tWR_ps = tWR_ps;
 	outpdimm->tWTR_ps = tWTR_ps;
 	outpdimm->tRFC_ps = tRFC_ps;
 	outpdimm->tRRD_ps = tRRD_ps;
 	outpdimm->tRC_ps = tRC_ps;
 	outpdimm->refresh_rate_ps = refresh_rate_ps;
 	outpdimm->tIS_ps = tIS_ps;
 	outpdimm->tIH_ps = tIH_ps;
 	outpdimm->tDS_ps = tDS_ps;
 	outpdimm->tDH_ps = tDH_ps;
 	outpdimm->tRTP_ps = tRTP_ps;
 	outpdimm->tDQSQ_max_ps = tDQSQ_max_ps;
 	outpdimm->tQHS_ps = tQHS_ps;

 	/* Determine common burst length for all DIMMs. */
 	temp1 = 0xff;
 	for (i = 0; i < number_of_dimms; i++) {
 		if (dimm_params[i].n_ranks) {
 			temp1 &= dimm_params[i].burst_lengths_bitmask;
 		}
 	}
 	outpdimm->all_DIMMs_burst_lengths_bitmask = temp1;

 	/* Determine if all DIMMs registered buffered. */
 	temp1 = temp2 = 0;
 	for (i = 0; i < number_of_dimms; i++) {
 		if (dimm_params[i].n_ranks) {
 			if (dimm_params[i].registered_dimm)
 				temp1 = 1;
 			if (!dimm_params[i].registered_dimm)
 				temp2 = 1;
 		}
 	}

 	outpdimm->all_DIMMs_registered = 0;
 	if (temp1 && !temp2) {
 		outpdimm->all_DIMMs_registered = 1;
 	}

 	outpdimm->all_DIMMs_unbuffered = 0;
 	if (!temp1 && temp2) {
 		outpdimm->all_DIMMs_unbuffered = 1;
 	}

 	/* CHECKME: */
 	if (!outpdimm->all_DIMMs_registered
 	    && !outpdimm->all_DIMMs_unbuffered) {
 		printf("ERROR:  Mix of registered buffered and unbuffered "
 				"DIMMs detected!\n");
 	}

 	/*
 	 * Compute a CAS latency suitable for all DIMMs
 	 *
 	 * Strategy for SPD-defined latencies: compute only
 	 * CAS latency defined by all DIMMs.
 	 */

 	/*
 	 * Step 1: find CAS latency common to all DIMMs using bitwise
 	 * operation.
 	 */
 	temp1 = 0xFF;
 	for (i = 0; i < number_of_dimms; i++) {
 		if (dimm_params[i].n_ranks) {
 			temp2 = 0;
 			temp2 |= 1 << dimm_params[i].caslat_X;
 			temp2 |= 1 << dimm_params[i].caslat_X_minus_1;
 			temp2 |= 1 << dimm_params[i].caslat_X_minus_2;
 			/*
 			 * FIXME: If there was no entry for X-2 (X-1) in
 			 * the SPD, then caslat_X_minus_2
 			 * (caslat_X_minus_1) contains either 255 or
 			 * 0xFFFFFFFF because that's what the glorious
 			 * __ilog2 function returns for an input of 0.
 			 * On 32-bit PowerPC, left shift counts with bit
 			 * 26 set (that the value of 255 or 0xFFFFFFFF
 			 * will have), cause the destination register to
 			 * be 0.  That is why this works.
 			 */
 			temp1 &= temp2;
 		}
 	}

 	/*
 	 * Step 2: check each common CAS latency against tCK of each
 	 * DIMM's SPD.
 	 */
 	lowest_good_caslat = 0;
 	temp2 = 0;
 	while (temp1) {
 		not_ok = 0;
 		temp2 =  __ilog2(temp1);
 		debug("checking common caslat = %u\n", temp2);

 		/* Check if this CAS latency will work on all DIMMs at tCK. */
 		for (i = 0; i < number_of_dimms; i++) {
 			if (!dimm_params[i].n_ranks) {
 				continue;
 			}
 			if (dimm_params[i].caslat_X == temp2) {
 				if (mclk_ps >= dimm_params[i].tCKmin_X_ps) {
 					debug("CL = %u ok on DIMM %u at tCK=%u"
 					    " ps with its tCKmin_X_ps of %u\n",
 					       temp2, i, mclk_ps,
 					       dimm_params[i].tCKmin_X_ps);
 					continue;
 				} else {
 					not_ok++;
 				}
 			}

 			if (dimm_params[i].caslat_X_minus_1 == temp2) {
 				unsigned int tCKmin_X_minus_1_ps
 					= dimm_params[i].tCKmin_X_minus_1_ps;
 				if (mclk_ps >= tCKmin_X_minus_1_ps) {
 					debug("CL = %u ok on DIMM %u at "
 						"tCK=%u ps with its "
 						"tCKmin_X_minus_1_ps of %u\n",
 					       temp2, i, mclk_ps,
 					       tCKmin_X_minus_1_ps);
 					continue;
 				} else {
 					not_ok++;
 				}
 			}

 			if (dimm_params[i].caslat_X_minus_2 == temp2) {
 				unsigned int tCKmin_X_minus_2_ps
 					= dimm_params[i].tCKmin_X_minus_2_ps;
 				if (mclk_ps >= tCKmin_X_minus_2_ps) {
 					debug("CL = %u ok on DIMM %u at "
 						"tCK=%u ps with its "
 						"tCKmin_X_minus_2_ps of %u\n",
 					       temp2, i, mclk_ps,
 					       tCKmin_X_minus_2_ps);
 					continue;
 				} else {
 					not_ok++;
 				}
 			}
 		}

 		if (!not_ok) {
 			lowest_good_caslat = temp2;
 		}

 		temp1 &= ~(1 << temp2);
 	}

 	debug("lowest common SPD-defined CAS latency = %u\n",
 	       lowest_good_caslat);
 	outpdimm->lowest_common_SPD_caslat = lowest_good_caslat;


 	/*
 	 * Compute a common 'de-rated' CAS latency.
 	 *
 	 * The strategy here is to find the *highest* dereated cas latency
 	 * with the assumption that all of the DIMMs will support a dereated
 	 * CAS latency higher than or equal to their lowest dereated value.
 	 */
 	temp1 = 0;
 	for (i = 0; i < number_of_dimms; i++) {
 		temp1 = max(temp1, dimm_params[i].caslat_lowest_derated);
 	}
 	outpdimm->highest_common_derated_caslat = temp1;
 	debug("highest common dereated CAS latency = %u\n", temp1);

 	/* Determine if all DIMMs ECC capable. */
 	temp1 = 1;
 	for (i = 0; i < number_of_dimms; i++) {
 		if (dimm_params[i].n_ranks && dimm_params[i].edc_config != 2) {
 			temp1 = 0;
 			break;
 		}
 	}
 	if (temp1) {
 		debug("all DIMMs ECC capable\n");
 	} else {
 		debug("Warning: not all DIMMs ECC capable, cant enable ECC\n");
 	}
 	outpdimm->all_DIMMs_ECC_capable = temp1;


 	/* FIXME: move to somewhere else to validate. */
 	if (mclk_ps > tCKmax_max_ps) {
 		printf("Warning: some of the installed DIMMs "
 				"can not operate this slowly.\n");
 		return 1;
 	}

 	/*
 	 * Compute additive latency.
 	 *
 	 * For DDR1, additive latency should be 0.
 	 *
 	 * For DDR2, with ODT enabled, use "a value" less than ACTTORW,
 	 *	which comes from Trcd, and also note that:
 	 *	    add_lat + caslat must be >= 4
 	 *
 	 * For DDR3, FIXME additive latency determination
 	 *
 	 * When to use additive latency for DDR2:
 	 *
 	 * I. Because you are using CL=3 and need to do ODT on writes and
 	 *    want functionality.
 	 *    1. Are you going to use ODT? (Does your board not have
 	 *      additional termination circuitry for DQ, DQS, DQS_,
 	 *      DM, RDQS, RDQS_ for x4/x8 configs?)
 	 *    2. If so, is your lowest supported CL going to be 3?
 	 *    3. If so, then you must set AL=1 because
 	 *
 	 *       WL >= 3 for ODT on writes
 	 *       RL = AL + CL
 	 *       WL = RL - 1
 	 *       ->
 	 *       WL = AL + CL - 1
 	 *       AL + CL - 1 >= 3
 	 *       AL + CL >= 4
 	 *  QED
 	 *
 	 *  RL >= 3 for ODT on reads
 	 *  RL = AL + CL
 	 *
 	 *  Since CL aren't usually less than 2, AL=0 is a minimum,
 	 *  so the WL-derived AL should be the  -- FIXME?
 	 *
 	 * II. Because you are using auto-precharge globally and want to
 	 *     use additive latency (posted CAS) to get more bandwidth.
 	 *     1. Are you going to use auto-precharge mode globally?
 	 *
 	 *        Use addtivie latency and compute AL to be 1 cycle less than
 	 *        tRCD, i.e. the READ or WRITE command is in the cycle
 	 *        immediately following the ACTIVATE command..
 	 *
 	 * III. Because you feel like it or want to do some sort of
 	 *      degraded-performance experiment.
 	 *     1.  Do you just want to use additive latency because you feel
 	 *         like it?
 	 *
 	 * Validation:  AL is less than tRCD, and within the other
 	 * read-to-precharge constraints.
 	 */

 	additive_latency = 0;

 #if defined(CONFIG_FSL_DDR2)
 	if (lowest_good_caslat < 4) {
 		additive_latency = picos_to_mclk(tRCD_ps) - lowest_good_caslat;
 		if (mclk_to_picos(additive_latency) > tRCD_ps) {
 			additive_latency = picos_to_mclk(tRCD_ps);
 			debug("setting additive_latency to %u because it was "
 				" greater than tRCD_ps\n", additive_latency);
 		}
 	}

 #elif defined(CONFIG_FSL_DDR3)
 error "FIXME determine additive latency for DDR3"
 #endif

 	/*
 	 * Validate additive latency
 	 * FIXME: move to somewhere else to validate
 	 *
 	 * AL <= tRCD(min)
 	 */
 	if (mclk_to_picos(additive_latency) > tRCD_ps) {
 		printf("Error: invalid additive latency exceeds tRCD(min).\n");
 		return 1;
 	}

 	/*
 	 * RL = CL + AL;  RL >= 3 for ODT_RD_CFG to be enabled
 	 * WL = RL - 1;  WL >= 3 for ODT_WL_CFG to be enabled
 	 * ADD_LAT (the register) must be set to a value less
 	 * than ACTTORW if WL = 1, then AL must be set to 1
 	 * RD_TO_PRE (the register) must be set to a minimum
 	 * tRTP + AL if AL is nonzero
 	 */

 	/*
 	 * Additive latency will be applied only if the memctl option to
 	 * use it.
 	 */
 	outpdimm->additive_latency = additive_latency;

 	return 0;
 }
	/*
	* Copyright 2008 Freescale Semiconductor, Inc.
	*
	* This program is free software; you can redistribute it and/or
	* modify it under the terms of the GNU General Public License
	* Version 2 as published by the Free Software Foundation.
	*/

	#include <common.h>
	#include <asm/fsl_ddr_sdram.h>

	#include "ddr.h"

	/*
	* compute_lowest_common_dimm_parameters()
	*
	* Determine the worst-case DIMM timing parameters from the set of DIMMs
	* whose parameters have been computed into the array pointed to
	* by dimm_params.
	*/
	unsigned int
	compute_lowest_common_dimm_parameters(const dimm_params_t *dimm_params,
	common_timing_params_t *outpdimm,
	unsigned int number_of_dimms)
	{
	unsigned int i;

	unsigned int tCKmin_X_ps = 0;
	unsigned int tCKmax_ps = 0xFFFFFFFF;
	unsigned int tCKmax_max_ps = 0;
	unsigned int tRCD_ps = 0;
	unsigned int tRP_ps = 0;
	unsigned int tRAS_ps = 0;
	unsigned int tWR_ps = 0;
	unsigned int tWTR_ps = 0;
	unsigned int tRFC_ps = 0;
	unsigned int tRRD_ps = 0;
	unsigned int tRC_ps = 0;
	unsigned int refresh_rate_ps = 0;
	unsigned int tIS_ps = 0;
	unsigned int tIH_ps = 0;
	unsigned int tDS_ps = 0;
	unsigned int tDH_ps = 0;
	unsigned int tRTP_ps = 0;
	unsigned int tDQSQ_max_ps = 0;
	unsigned int tQHS_ps = 0;

	unsigned int temp1, temp2;
	unsigned int lowest_good_caslat;
	unsigned int additive_latency = 0;
	const unsigned int mclk_ps = get_memory_clk_period_ps();
	unsigned int not_ok;

	debug("using mclk_ps = %u\n", mclk_ps);

	temp1 = 0;
	for (i = 0; i < number_of_dimms; i++) {
	/*
	* If there are no ranks on this DIMM,
	* it probably doesn't exist, so skip it.
	*/
	if (dimm_params[i].n_ranks == 0) {
	temp1++;
	continue;
	}

	/*
	* Find minimum tCKmax_ps to find fastest slow speed,
	* i.e., this is the slowest the whole system can go.
	*/
	tCKmax_ps = min(tCKmax_ps, dimm_params[i].tCKmax_ps);

	/* Either find maximum value to determine slowest
	* speed, delay, time, period, etc */
	tCKmin_X_ps = max(tCKmin_X_ps, dimm_params[i].tCKmin_X_ps);
	tCKmax_max_ps = max(tCKmax_max_ps, dimm_params[i].tCKmax_ps);
	tRCD_ps = max(tRCD_ps, dimm_params[i].tRCD_ps);
	tRP_ps = max(tRP_ps, dimm_params[i].tRP_ps);
	tRAS_ps = max(tRAS_ps, dimm_params[i].tRAS_ps);
	tWR_ps = max(tWR_ps, dimm_params[i].tWR_ps);
	tWTR_ps = max(tWTR_ps, dimm_params[i].tWTR_ps);
	tRFC_ps = max(tRFC_ps, dimm_params[i].tRFC_ps);
	tRRD_ps = max(tRRD_ps, dimm_params[i].tRRD_ps);
	tRC_ps = max(tRC_ps, dimm_params[i].tRC_ps);
	tIS_ps = max(tIS_ps, dimm_params[i].tIS_ps);
	tIH_ps = max(tIH_ps, dimm_params[i].tIH_ps);
	tDS_ps = max(tDS_ps, dimm_params[i].tDS_ps);
	tDH_ps = max(tDH_ps, dimm_params[i].tDH_ps);
	tRTP_ps = max(tRTP_ps, dimm_params[i].tRTP_ps);
	tQHS_ps = max(tQHS_ps, dimm_params[i].tQHS_ps);
	refresh_rate_ps = max(refresh_rate_ps,
	dimm_params[i].refresh_rate_ps);

	/*
	* Find maximum tDQSQ_max_ps to find slowest.
	*
	* FIXME: is finding the slowest value the correct
	* strategy for this parameter?
	*/
	tDQSQ_max_ps = max(tDQSQ_max_ps, dimm_params[i].tDQSQ_max_ps);
	}

	outpdimm->ndimms_present = number_of_dimms - temp1;

	if (temp1 == number_of_dimms) {
	debug("no dimms this memory controller\n");
	return 0;
	}

	outpdimm->tCKmin_X_ps = tCKmin_X_ps;
	outpdimm->tCKmax_ps = tCKmax_ps;
	outpdimm->tCKmax_max_ps = tCKmax_max_ps;
	outpdimm->tRCD_ps = tRCD_ps;
	outpdimm->tRP_ps = tRP_ps;
	outpdimm->tRAS_ps = tRAS_ps;
	outpdimm->tWR_ps = tWR_ps;
	outpdimm->tWTR_ps = tWTR_ps;
	outpdimm->tRFC_ps = tRFC_ps;
	outpdimm->tRRD_ps = tRRD_ps;
	outpdimm->tRC_ps = tRC_ps;
	outpdimm->refresh_rate_ps = refresh_rate_ps;
	outpdimm->tIS_ps = tIS_ps;
	outpdimm->tIH_ps = tIH_ps;
	outpdimm->tDS_ps = tDS_ps;
	outpdimm->tDH_ps = tDH_ps;
	outpdimm->tRTP_ps = tRTP_ps;
	outpdimm->tDQSQ_max_ps = tDQSQ_max_ps;
	outpdimm->tQHS_ps = tQHS_ps;

	/* Determine common burst length for all DIMMs. */
	temp1 = 0xff;
	for (i = 0; i < number_of_dimms; i++) {
	if (dimm_params[i].n_ranks) {
	temp1 &= dimm_params[i].burst_lengths_bitmask;
	}
	}
	outpdimm->all_DIMMs_burst_lengths_bitmask = temp1;

	/* Determine if all DIMMs registered buffered. */
	temp1 = temp2 = 0;
	for (i = 0; i < number_of_dimms; i++) {
	if (dimm_params[i].n_ranks) {
	if (dimm_params[i].registered_dimm)
	temp1 = 1;
	if (!dimm_params[i].registered_dimm)
	temp2 = 1;
	}
	}

	outpdimm->all_DIMMs_registered = 0;
	if (temp1 && !temp2) {
	outpdimm->all_DIMMs_registered = 1;
	}

	outpdimm->all_DIMMs_unbuffered = 0;
	if (!temp1 && temp2) {
	outpdimm->all_DIMMs_unbuffered = 1;
	}

	/* CHECKME: */
	if (!outpdimm->all_DIMMs_registered
	&& !outpdimm->all_DIMMs_unbuffered) {
	printf("ERROR: Mix of registered buffered and unbuffered "
	"DIMMs detected!\n");
	}

	/*
	* Compute a CAS latency suitable for all DIMMs
	*
	* Strategy for SPD-defined latencies: compute only
	* CAS latency defined by all DIMMs.
	*/

	/*
	* Step 1: find CAS latency common to all DIMMs using bitwise
	* operation.
	*/
	temp1 = 0xFF;
	for (i = 0; i < number_of_dimms; i++) {
	if (dimm_params[i].n_ranks) {
	temp2 = 0;
	temp2 \|= 1 << dimm_params[i].caslat_X;
	temp2 \|= 1 << dimm_params[i].caslat_X_minus_1;
	temp2 \|= 1 << dimm_params[i].caslat_X_minus_2;
	/*
	* FIXME: If there was no entry for X-2 (X-1) in
	* the SPD, then caslat_X_minus_2
	* (caslat_X_minus_1) contains either 255 or
	* 0xFFFFFFFF because that's what the glorious
	* __ilog2 function returns for an input of 0.
	* On 32-bit PowerPC, left shift counts with bit
	* 26 set (that the value of 255 or 0xFFFFFFFF
	* will have), cause the destination register to
	* be 0. That is why this works.
	*/
	temp1 &= temp2;
	}
	}

	/*
	* Step 2: check each common CAS latency against tCK of each
	* DIMM's SPD.
	*/
	lowest_good_caslat = 0;
	temp2 = 0;
	while (temp1) {
	not_ok = 0;
	temp2 = __ilog2(temp1);
	debug("checking common caslat = %u\n", temp2);

	/* Check if this CAS latency will work on all DIMMs at tCK. */
	for (i = 0; i < number_of_dimms; i++) {
	if (!dimm_params[i].n_ranks) {
	continue;
	}
	if (dimm_params[i].caslat_X == temp2) {
	if (mclk_ps >= dimm_params[i].tCKmin_X_ps) {
	debug("CL = %u ok on DIMM %u at tCK=%u"
	" ps with its tCKmin_X_ps of %u\n",
	temp2, i, mclk_ps,
	dimm_params[i].tCKmin_X_ps);
	continue;
	} else {
	not_ok++;
	}
	}

	if (dimm_params[i].caslat_X_minus_1 == temp2) {
	unsigned int tCKmin_X_minus_1_ps
	= dimm_params[i].tCKmin_X_minus_1_ps;
	if (mclk_ps >= tCKmin_X_minus_1_ps) {
	debug("CL = %u ok on DIMM %u at "
	"tCK=%u ps with its "
	"tCKmin_X_minus_1_ps of %u\n",
	temp2, i, mclk_ps,
	tCKmin_X_minus_1_ps);
	continue;
	} else {
	not_ok++;
	}
	}

	if (dimm_params[i].caslat_X_minus_2 == temp2) {
	unsigned int tCKmin_X_minus_2_ps
	= dimm_params[i].tCKmin_X_minus_2_ps;
	if (mclk_ps >= tCKmin_X_minus_2_ps) {
	debug("CL = %u ok on DIMM %u at "
	"tCK=%u ps with its "
	"tCKmin_X_minus_2_ps of %u\n",
	temp2, i, mclk_ps,
	tCKmin_X_minus_2_ps);
	continue;
	} else {
	not_ok++;
	}
	}
	}

	if (!not_ok) {
	lowest_good_caslat = temp2;
	}

	temp1 &= ~(1 << temp2);
	}

	debug("lowest common SPD-defined CAS latency = %u\n",
	lowest_good_caslat);
	outpdimm->lowest_common_SPD_caslat = lowest_good_caslat;


	/*
	* Compute a common 'de-rated' CAS latency.
	*
	* The strategy here is to find the highest dereated cas latency
	* with the assumption that all of the DIMMs will support a dereated
	* CAS latency higher than or equal to their lowest dereated value.
	*/
	temp1 = 0;
	for (i = 0; i < number_of_dimms; i++) {
	temp1 = max(temp1, dimm_params[i].caslat_lowest_derated);
	}
	outpdimm->highest_common_derated_caslat = temp1;
	debug("highest common dereated CAS latency = %u\n", temp1);

	/* Determine if all DIMMs ECC capable. */
	temp1 = 1;
	for (i = 0; i < number_of_dimms; i++) {
	if (dimm_params[i].n_ranks && dimm_params[i].edc_config != 2) {
	temp1 = 0;
	break;
	}
	}
	if (temp1) {
	debug("all DIMMs ECC capable\n");
	} else {
	debug("Warning: not all DIMMs ECC capable, cant enable ECC\n");
	}
	outpdimm->all_DIMMs_ECC_capable = temp1;


	/* FIXME: move to somewhere else to validate. */
	if (mclk_ps > tCKmax_max_ps) {
	printf("Warning: some of the installed DIMMs "
	"can not operate this slowly.\n");
	return 1;
	}

	/*
	* Compute additive latency.
	*
	* For DDR1, additive latency should be 0.
	*
	* For DDR2, with ODT enabled, use "a value" less than ACTTORW,
	* which comes from Trcd, and also note that:
	* add_lat + caslat must be >= 4
	*
	* For DDR3, FIXME additive latency determination
	*
	* When to use additive latency for DDR2:
	*
	* I. Because you are using CL=3 and need to do ODT on writes and
	* want functionality.
	* 1. Are you going to use ODT? (Does your board not have
	* additional termination circuitry for DQ, DQS, DQS_,
	* DM, RDQS, RDQS_ for x4/x8 configs?)
	* 2. If so, is your lowest supported CL going to be 3?
	* 3. If so, then you must set AL=1 because
	*
	* WL >= 3 for ODT on writes
	* RL = AL + CL
	* WL = RL - 1
	* ->
	* WL = AL + CL - 1
	* AL + CL - 1 >= 3
	* AL + CL >= 4
	* QED
	*
	* RL >= 3 for ODT on reads
	* RL = AL + CL
	*
	* Since CL aren't usually less than 2, AL=0 is a minimum,
	* so the WL-derived AL should be the -- FIXME?
	*
	* II. Because you are using auto-precharge globally and want to
	* use additive latency (posted CAS) to get more bandwidth.
	* 1. Are you going to use auto-precharge mode globally?
	*
	* Use addtivie latency and compute AL to be 1 cycle less than
	* tRCD, i.e. the READ or WRITE command is in the cycle
	* immediately following the ACTIVATE command..
	*
	* III. Because you feel like it or want to do some sort of
	* degraded-performance experiment.
	* 1. Do you just want to use additive latency because you feel
	* like it?
	*
	* Validation: AL is less than tRCD, and within the other
	* read-to-precharge constraints.
	*/

	additive_latency = 0;

	#if defined(CONFIG_FSL_DDR2)
	if (lowest_good_caslat < 4) {
	additive_latency = picos_to_mclk(tRCD_ps) - lowest_good_caslat;
	if (mclk_to_picos(additive_latency) > tRCD_ps) {
	additive_latency = picos_to_mclk(tRCD_ps);
	debug("setting additive_latency to %u because it was "
	" greater than tRCD_ps\n", additive_latency);
	}
	}

	#elif defined(CONFIG_FSL_DDR3)
	error "FIXME determine additive latency for DDR3"
	#endif

	/*
	* Validate additive latency
	* FIXME: move to somewhere else to validate
	*
	* AL <= tRCD(min)
	*/
	if (mclk_to_picos(additive_latency) > tRCD_ps) {
	printf("Error: invalid additive latency exceeds tRCD(min).\n");
	return 1;
	}

	/*
	* RL = CL + AL; RL >= 3 for ODT_RD_CFG to be enabled
	* WL = RL - 1; WL >= 3 for ODT_WL_CFG to be enabled
	* ADD_LAT (the register) must be set to a value less
	* than ACTTORW if WL = 1, then AL must be set to 1
	* RD_TO_PRE (the register) must be set to a minimum
	* tRTP + AL if AL is nonzero
	*/

	/*
	* Additive latency will be applied only if the memctl option to
	* use it.
	*/
	outpdimm->additive_latency = additive_latency;

	return 0;
	}