soc/intel/common/blk/memory: Make mixed topo work

When using a mixed memory topology with DDR4, it's not possible to boot
when no DIMMs are installed, even though memory-down is available. This
happens because the DIMM SPD length defaults to 256 when no DIMM SPD is
available. Relax the length check when no DIMMs are present to overcome
this problem.

Tested on system76/lemp10. Unit boots with and without DIMM installed.

Change-Id: I1cabf64fade1c06a44b6c3892659d54febc7a79a
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Tested-by: Tim Crawford <tcrawford@system76.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/60800
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>
Reviewed-by: Tim Crawford <tcrawford@system76.com>

src/mainboard/system76/lemp10/romstage.c

@@ -13,7 +13,6 @@ void mainboard_memory_init_params(FSPM_UPD *mupd)
 		.topo = MEM_TOPO_MIXED,
 		.cbfs_index = 0,
 		.smbus = {
-			[0] = { .addr_dimm[0] = 0x50, },
 			[1] = { .addr_dimm[0] = 0x52, },
 		},
 	};

src/soc/intel/common/block/memory/meminit.c

@@ -6,6 +6,7 @@
 #include <commonlib/region.h>
 #include <spd_bin.h>
 #include <string.h>
+#include <types.h>
 
 _Static_assert(CONFIG_MRC_CHANNEL_WIDTH > 0, "MRC channel width must be >0!");
 _Static_assert(CONFIG_DATA_BUS_WIDTH > 0, "Data bus width must be >0!");
@@ -93,7 +94,7 @@ static void read_spd_md(const struct soc_mem_cfg *soc_mem_cfg, const struct mem_
 
 #define CH_DIMM_OFFSET(ch, dimm)	((ch) * CONFIG_DIMMS_PER_CHANNEL + (dimm))
 
-static void read_spd_dimm(const struct soc_mem_cfg *soc_mem_cfg, const struct mem_spd *info,
+static bool read_spd_dimm(const struct soc_mem_cfg *soc_mem_cfg, const struct mem_spd *info,
 			bool half_populated, struct mem_channel_data *channel_data,
 			size_t *spd_len)
 {
@@ -109,7 +110,7 @@ static void read_spd_dimm(const struct soc_mem_cfg *soc_mem_cfg, const struct me
 	uint32_t pop_mask = 0;
 
 	if (!(info->topo & MEM_TOPO_DIMM_MODULE))
-		return;
+		return false;
 
 	for (ch = 0; ch < num_phys_ch; ch++) {
 		for (dimm = 0; dimm < CONFIG_DIMMS_PER_CHANNEL; dimm++) {
@@ -137,6 +138,8 @@ static void read_spd_dimm(const struct soc_mem_cfg *soc_mem_cfg, const struct me
 	}
 
 	channel_data->ch_population_flags |= populated_mask_to_flag(pop_mask, num_phys_ch);
+
+	return pop_mask != 0;
 }
 
 void mem_populate_channel_data(const struct soc_mem_cfg *soc_mem_cfg,
@@ -145,11 +148,12 @@ void mem_populate_channel_data(const struct soc_mem_cfg *soc_mem_cfg,
 				struct mem_channel_data *data)
 {
 	size_t spd_md_len = 0, spd_dimm_len = 0;
+	bool have_dimms;
 
 	memset(data, 0, sizeof(*data));
 
 	read_spd_md(soc_mem_cfg, spd_info, half_populated, data, &spd_md_len);
-	read_spd_dimm(soc_mem_cfg, spd_info, half_populated, data, &spd_dimm_len);
+	have_dimms = read_spd_dimm(soc_mem_cfg, spd_info, half_populated, data, &spd_dimm_len);
 
 	if (data->ch_population_flags == NO_CHANNEL_POPULATED)
 		die("No channels are populated. Incorrect memory configuration!\n");
@@ -161,11 +165,12 @@ void mem_populate_channel_data(const struct soc_mem_cfg *soc_mem_cfg,
 	} else {
 		/*
 		 * SPD lengths must match for CBFS and EEPROM SPD for mixed
-		 * topology.
+		 * topology. Skip this check when no DIMMs are installed.
 		 */
-		if (spd_md_len != spd_dimm_len)
+		if (have_dimms && spd_md_len != spd_dimm_len)
 			die("Length of SPD does not match for mixed topology!\n");
 
+		/* Use memory-down SPD length in case there are no DIMMs installed */
 		data->spd_len = spd_md_len;
 	}
 }