Documentation/northbridge/intel/haswell/mrc.bin.md: add SPD addresses

Change-Id: I8bf81637f582373d9bba1d47fe5205d459151f3e
Signed-off-by: Daniel Maslowski <dan@orangecms.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/32473
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Patrick Rudolph <siro@das-labor.org>

1 files changed, 77 insertions, 0 deletions

diff --git a/Documentation/northbridge/intel/haswell/mrc.bin.md b/Documentation/northbridge/intel/haswell/mrc.bin.md
index 36ab4c4385dd..edfe4b8b84a6 100644
--- a/Documentation/northbridge/intel/haswell/mrc.bin.md
+++ b/Documentation/northbridge/intel/haswell/mrc.bin.md
@@ -27,6 +27,83 @@ Now, place `mrc.bin` in the root of the coreboot directory.
 Alternatively, place `mrc.bin` anywhere you want, and set `MRC_FILE` to
 its location when building coreboot.
 
+## SPD Addresses
+
+When porting a board from vendor firmware, the SPD addresses can be obtained
+through `i2c-tools`, which can be found in many GNU/Linux distributions. A more
+[detailed description](https://hannuhartikainen.fi/blog/hacking-ddr3-spd/) of
+the procedure and beyond can be found in
+[Hannu Hartikainen's blog](https://hannuhartikainen.fi).
+
+First load the kernel modules:
+
+```bash
+modprobe i2c-dev
+modprobe eeprom
+```
+
+Find the SMBus and the addresses of the DIMM's EEPROMs (example output):
+```bash
+$ decode-dimms | grep Decoding
+Decoding EEPROM: /sys/bus/i2c/drivers/eeprom/7-0050
+Decoding EEPROM: /sys/bus/i2c/drivers/eeprom/7-0052
+```
+
+Alternatively, look at the sys filesystem:
+```bash
+$ ls -l /sys/bus/i2c/drivers/eeprom/
+total 0
+lrwxrwxrwx 1 root root    0 Apr  4 01:46 6-0050 -> ../../../../devices/pci0000:00/0000:00:02.0/drm/card0/card0-eDP-1/i2c-6/6-0050/
+lrwxrwxrwx 1 root root    0 Apr  4 01:46 7-0050 -> ../../../../devices/pci0000:00/0000:00:1f.3/i2c-7/7-0050/
+lrwxrwxrwx 1 root root    0 Apr  4 01:46 7-0052 -> ../../../../devices/pci0000:00/0000:00:1f.3/i2c-7/7-0052/
+--w------- 1 root root 4096 Apr  4 01:47 bind
+lrwxrwxrwx 1 root root    0 Apr  4 01:47 module -> ../../../../module/eeprom/
+--w------- 1 root root 4096 Apr  4 01:46 uevent
+--w------- 1 root root 4096 Apr  4 01:47 unbind
+```
+
+The correct I2C bus is 7 in this case, and the EEPROMs are at `0x50` and `0x52`.
+Note that the above values are actually hex values.
+
+You can check the correctness of the SMBus and the addresses of the EEPROMs via
+`i2cdetect`:
+
+```bash
+$ i2cdetect -l
+i2c-3   unknown         i915 gmbus dpc                          N/A
+i2c-1   unknown         i915 gmbus vga                          N/A
+i2c-6   unknown         DPDDC-A                                 N/A
+i2c-4   unknown         i915 gmbus dpb                          N/A
+i2c-2   unknown         i915 gmbus panel                        N/A
+i2c-0   unknown         i915 gmbus ssc                          N/A
+i2c-7   unknown         SMBus I801 adapter at f040              N/A
+i2c-5   unknown         i915 gmbus dpd                          N/A
+```
+
+Probing the SMBus:
+
+```bash
+$ i2cdetect -r 7
+WARNING! This program can confuse your I2C bus, cause data loss and worse!
+I will probe file /dev/i2c-7 using receive byte commands.
+I will probe address range 0x03-0x77.
+Continue? [Y/n]
+     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
+00:          -- -- -- -- -- -- -- -- -- -- -- -- --
+10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
+20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
+30: 30 -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
+40: -- -- -- -- 44 -- -- -- -- -- -- -- -- -- -- --
+50: UU -- UU -- -- -- -- -- -- -- -- -- -- -- -- --
+60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
+70: -- -- -- -- -- -- -- --
+```
+
+The SPD addresses need to be left-shifted by 1 for `mrc.bin`, i.e., multiplied
+by 2. For example, if the addresses read through `i2c-tools` when booted from
+vendor firmware are `0x50` and `0x52`, the correct values would be `0xa0` and
+`0xa4`. This is because the I2C addresses are 7 bits long.
+
 ## ECC DRAM
 
 When `mrc.bin` has finished executing, ECC is active on the channels