mb/google/corsola: Get RAM code from ADC

On Chromebooks the RAM code is implemented by the resistor straps
that we can read and decode from ADC. For Corsola the RAM code can be
read from ADC channel 2 and 3.

TEST=build pass
BUG=b:202871018

Signed-off-by: Rex-BC Chen <rex-bc.chen@mediatek.com>
Change-Id: I485c32dec7b425b604b4063d742a0e37d3961513
Reviewed-on: https://review.coreboot.org/c/coreboot/+/59570
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Yu-Ping Wu <yupingso@google.com>

src/mainboard/google/corsola/Makefile.inc

@@ -7,11 +7,13 @@ verstage-y += chromeos.c
 verstage-y += reset.c
 
 romstage-y += memlayout.ld
+romstage-y += boardid.c
 romstage-y += chromeos.c
 romstage-y += regulator.c
 romstage-y += romstage.c
 
 ramstage-y += memlayout.ld
+ramstage-y += boardid.c
 ramstage-y += chromeos.c
 ramstage-y += mainboard.c
 ramstage-y += regulator.c

src/mainboard/google/corsola/boardid.c

@@ -0,0 +1,68 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#include <assert.h>
+#include <boardid.h>
+#include <console/console.h>
+#include <soc/auxadc.h>
+
+/* board_id is provided by ec/google/chromeec/ec_boardid.c */
+
+#define ADC_LEVELS 12
+
+enum {
+	/* RAM IDs */
+	RAM_ID_LOW_CHANNEL = 2,
+	RAM_ID_HIGH_CHANNEL = 3,
+};
+
+static const unsigned int ram_voltages[ADC_LEVELS] = {
+	/* ID : Voltage (unit: uV) */
+	[0]  =   74300,
+	[1]  =  211700,
+	[2]  =  318800,
+	[3]  =  428600,
+	[4]  =  541700,
+	[5]  =  665800,
+	[6]  =  781400,
+	[7]  =  900000,
+	[8]  = 1023100,
+	[9]  = 1137000,
+	[10] = 1240000,
+	[11] = 1342600,
+};
+
+static const unsigned int *adc_voltages[] = {
+	[RAM_ID_LOW_CHANNEL] = ram_voltages,
+	[RAM_ID_HIGH_CHANNEL] = ram_voltages,
+};
+
+static uint32_t get_adc_index(unsigned int channel)
+{
+	unsigned int value = auxadc_get_voltage_uv(channel);
+
+	assert(channel < ARRAY_SIZE(adc_voltages));
+	const unsigned int *voltages = adc_voltages[channel];
+	assert(voltages);
+
+	/* Find the closest voltage */
+	uint32_t id;
+	for (id = 0; id < ADC_LEVELS - 1; id++)
+		if (value < (voltages[id] + voltages[id + 1]) / 2)
+			break;
+
+	printk(BIOS_DEBUG, "ADC[%u]: Raw value=%u ID=%u\n", channel, value, id);
+	return id;
+}
+
+uint32_t ram_code(void)
+{
+	static uint32_t cached_ram_code = BOARD_ID_INIT;
+
+	if (cached_ram_code == BOARD_ID_INIT) {
+		cached_ram_code = (get_adc_index(RAM_ID_HIGH_CHANNEL) << 4 |
+				   get_adc_index(RAM_ID_LOW_CHANNEL));
+		printk(BIOS_DEBUG, "RAM Code: %#02x\n", cached_ram_code);
+	}
+
+	return cached_ram_code;
+}