[M] Change in coreboot[main]: soc/intel/alderlake: Add function to force disable memory channels

[Subrata Banik (Code Review)]

Subrata Banik has submitted this change. ( https://review.coreboot.org/c/coreboot/+/85529?usp=email )

Change subject: soc/intel/alderlake: Add function to force disable memory channels
......................................................................

soc/intel/alderlake: Add function to force disable memory channels

Add a function `mem_init_override_channel_mask` to disable memory
channels based on given bitmap where each bit represents a memory
channel. A set bit will disable corresponding memory channel. Variants
can override this bitmap by selecting `ENFORCE_MEM_CHANNEL_DISABLE` and
implementing `mb_get_channel_disable_mask` to return the bitmap.

BUG=b:379311559
TEST=Make sure that channel mask is applied correctly.

Lotso without any channel mask:
```
lotso-rev0 ~ # dmidecode -t 17 | grep -E "(Locator: C|Size)"
        Size: 2 GB
        Locator: Channel-0-DIMM-0
        Size: 2 GB
        Locator: Channel-1-DIMM-0
        Size: 2 GB
        Locator: Channel-2-DIMM-0
        Size: 2 GB
        Locator: Channel-3-DIMM-0
        Size: 2 GB
        Locator: Channel-0-DIMM-0
        Size: 2 GB
        Locator: Channel-1-DIMM-0
        Size: 2 GB
        Locator: Channel-2-DIMM-0
        Size: 2 GB
        Locator: Channel-3-DIMM-0

lotso-rev0 ~ # dmidecode -t 17 | grep Size | wc -l
8
```

Lotso with channel 2 & 3 masked:
```
lotso-rev0 ~ # dmidecode -t 17 | grep -E "(Locator: C|Size)"
        Size: 2 GB
        Locator: Channel-0-DIMM-0
        Size: 2 GB
        Locator: Channel-1-DIMM-0
        Size: 2 GB
        Locator: Channel-0-DIMM-0
        Size: 2 GB
        Locator: Channel-1-DIMM-0

lotso-rev0 ~ # dmidecode -t 17 | grep Size | wc -l
4
```

Change-Id: Ibfeca4509cb3d88bc1bac2ac2d480e665d895bc5
Signed-off-by: Kapil Porwal 
Reviewed-on: https://review.coreboot.org/c/coreboot/+/85529
Reviewed-by: Subrata Banik 
Tested-by: build bot (Jenkins) 
Reviewed-by: Dinesh Gehlot 
Reviewed-by: Jayvik Desai 
---
M src/soc/intel/alderlake/Kconfig
M src/soc/intel/alderlake/include/soc/meminit.h
M src/soc/intel/alderlake/meminit.c
3 files changed, 54 insertions(+), 0 deletions(-)

Approvals:
  build bot (Jenkins): Verified
  Dinesh Gehlot: Looks good to me, approved
  Subrata Banik: Looks good to me, approved
  Jayvik Desai: Looks good to me, approved

diff --git a/src/soc/intel/alderlake/Kconfig b/src/soc/intel/alderlake/Kconfig
index f6e9182..15f347f 100644
--- a/src/soc/intel/alderlake/Kconfig
+++ b/src/soc/intel/alderlake/Kconfig
@@ -441,6 +441,14 @@
    int
    default 16

+config ENFORCE_MEM_CHANNEL_DISABLE
+	bool
+	default n
+	help
+	  Select this option to disable certain memory channels on demand. If
+	  selected, A function named mb_get_channel_disable_mask() must be
+	  implemented to return the bit map of memory channels to disable.
+
 config ALDERLAKE_ENABLE_SOC_WORKAROUND
    bool
    default y
diff --git a/src/soc/intel/alderlake/include/soc/meminit.h b/src/soc/intel/alderlake/include/soc/meminit.h
index 1d9eaf9..97fb77c 100644
--- a/src/soc/intel/alderlake/include/soc/meminit.h
+++ b/src/soc/intel/alderlake/include/soc/meminit.h
@@ -116,4 +116,16 @@
 void memcfg_init(FSPM_UPD *memupd, const struct mb_cfg *mb_cfg,
    	 const struct mem_spd *spd_info, bool half_populated);

+/*
+ * This function is expected to return a bitmap of memory channels to
+ * disable. A set bit will disable corresponding memory channel.
+ * Variants can override this bitmap by selecting
+ * `ENFORCE_MEM_CHANNEL_DISABLE` and implementing this function.
+ */
+#if CONFIG(ENFORCE_MEM_CHANNEL_DISABLE)
+uint8_t mb_get_channel_disable_mask(void);
+#else
+static inline uint8_t mb_get_channel_disable_mask(void) { return 0; }
+#endif
+
 #endif /* _SOC_ALDERLAKE_MEMINIT_H_ */
diff --git a/src/soc/intel/alderlake/meminit.c b/src/soc/intel/alderlake/meminit.c
index 35c3252..6b3143e 100644
--- a/src/soc/intel/alderlake/meminit.c
+++ b/src/soc/intel/alderlake/meminit.c
@@ -233,6 +233,39 @@
    mem_init_dqs_upds(mem_cfg, NULL, mb_cfg, true);
 }

+/*
+ * A memory channel will be disabled if corresponding bit in
+ * ch_disable_mask is set.
+ */
+static void mem_init_override_channel_mask(FSP_M_CONFIG *mem_cfg)
+{
+	uint8_t *disable_channel_upds[MRC_CHANNELS] = {
+		&mem_cfg->DisableMc0Ch0,
+		&mem_cfg->DisableMc0Ch1,
+		&mem_cfg->DisableMc0Ch2,
+		&mem_cfg->DisableMc0Ch3,
+		&mem_cfg->DisableMc1Ch0,
+		&mem_cfg->DisableMc1Ch1,
+		&mem_cfg->DisableMc1Ch2,
+		&mem_cfg->DisableMc1Ch3,
+	};
+
+	uint8_t ch_disable_mask = mb_get_channel_disable_mask();
+	if (ch_disable_mask == 0)
+		return;
+
+	/* Mc0Ch0 cannot be disabled */
+	if (ch_disable_mask & BIT(0)) {
+		printk(BIOS_ERR, "Cannot disable the first memory channel (Mc0Ch0).\n");
+		return;
+	}
+
+	for (size_t ch = 0; ch < MRC_CHANNELS; ch++) {
+		if (ch_disable_mask & BIT(ch))
+			*disable_channel_upds[ch] = 1;
+	}
+}
+
 void memcfg_init(FSPM_UPD *memupd, const struct mb_cfg *mb_cfg,
    	 const struct mem_spd *spd_info, bool half_populated)
 {
@@ -283,6 +316,7 @@
    mem_populate_channel_data(memupd, &soc_mem_cfg[mb_cfg->type], spd_info, half_populated,
    		&data);
    mem_init_spd_upds(mem_cfg, &data);
+	mem_init_override_channel_mask(mem_cfg);
    mem_init_dq_upds(mem_cfg, &data, mb_cfg, dq_dqs_auto_detect);
    mem_init_dqs_upds(mem_cfg, &data, mb_cfg, dq_dqs_auto_detect);
 }