mb/siemens/mc_ehl: Make DRAM population configurable

There can be mainboard variants, which are only equipped with
half-populated DRAM. For this reason, the meminit parameter for
populatation should be adjustable. The default setting remains at
full-populated DRAM. At mainboard variant level a different selection
via individual input paths can be made.

Change-Id: I390bbfa680b5505bb2230fa0740720bd9dd1fafb
Signed-off-by: Mario Scheithauer <mario.scheithauer@siemens.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/76244
Reviewed-by: Eric Lai <eric_lai@quanta.corp-partner.google.com>
Reviewed-by: Jan Samek <jan.samek@siemens.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/mainboard/siemens/mc_ehl/romstage_fsp_params.c

@@ -10,6 +10,11 @@
 #include <string.h>
 #include <types.h>
 
+bool __weak half_populated(void)
+{
+	return false;
+}
+
 void mainboard_memory_init_params(FSPM_UPD *memupd)
 {
 	static struct spd_info spd_info;
@@ -29,7 +34,7 @@ void mainboard_memory_init_params(FSPM_UPD *memupd)
 		die("SPD in HW-Info not valid!\n");
 	}
 	/* Initialize variant specific configurations */
-	memcfg_init(&memupd->FspmConfig, board_cfg, &spd_info, false);
+	memcfg_init(&memupd->FspmConfig, board_cfg, &spd_info, half_populated());
 
 	/* Enable Row-Hammer prevention */
 	memupd->FspmConfig.RhPrevention = 1;

src/mainboard/siemens/mc_ehl/variants/baseboard/include/baseboard/variants.h

@@ -15,6 +15,9 @@ const struct pad_config *variant_early_gpio_table(size_t *num);
 /* This function returns SPD related FSP-M mainboard configs */
 const struct mb_cfg *variant_memcfg_config(void);
 
+/* This function can select half-populate DRAM */
+bool half_populated(void);
+
 /* The following function performs board specific things. */
 void variant_mainboard_final(void);