Error Detection And Correction (EDAC) Devices

Main Concepts used at the EDAC subsystem

There are several things to be aware of that aren’t at all obvious, like sockets, *socket sets, banks, rows, chip-select rows, channels, etc...

These are some of the many terms that are thrown about that don’t always mean what people think they mean (Inconceivable!). In the interest of creating a common ground for discussion, terms and their definitions will be established.

• Memory devices

The individual DRAM chips on a memory stick. These devices commonly output 4 and 8 bits each (x4, x8). Grouping several of these in parallel provides the number of bits that the memory controller expects: typically 72 bits, in order to provide 64 bits + 8 bits of ECC data.

• Memory Stick

A printed circuit board that aggregates multiple memory devices in parallel. In general, this is the Field Replaceable Unit (FRU) which gets replaced, in the case of excessive errors. Most often it is also called DIMM (Dual Inline Memory Module).

• Memory Socket

A physical connector on the motherboard that accepts a single memory stick. Also called as “slot” on several datasheets.

• Channel

A memory controller channel, responsible to communicate with a group of DIMMs. Each channel has its own independent control (command) and data bus, and can be used independently or grouped with other channels.

• Branch

It is typically the highest hierarchy on a Fully-Buffered DIMM memory controller. Typically, it contains two channels. Two channels at the same branch can be used in single mode or in lockstep mode. When lockstep is enabled, the cacheline is doubled, but it generally brings some performance penalty. Also, it is generally not possible to point to just one memory stick when an error occurs, as the error correction code is calculated using two DIMMs instead of one. Due to that, it is capable of correcting more errors than on single mode.

• Single-channel

The data accessed by the memory controller is contained into one dimm only. E. g. if the data is 64 bits-wide, the data flows to the CPU using one 64 bits parallel access. Typically used with SDR, DDR, DDR2 and DDR3 memories. FB-DIMM and RAMBUS use a different concept for channel, so this concept doesn’t apply there.

• Double-channel

The data size accessed by the memory controller is interlaced into two dimms, accessed at the same time. E. g. if the DIMM is 64 bits-wide (72 bits with ECC), the data flows to the CPU using a 128 bits parallel access.

• Chip-select row

This is the name of the DRAM signal used to select the DRAM ranks to be accessed. Common chip-select rows for single channel are 64 bits, for dual channel 128 bits. It may not be visible by the memory controller, as some DIMM types have a memory buffer that can hide direct access to it from the Memory Controller.

• Single-Ranked stick

A Single-ranked stick has 1 chip-select row of memory. Motherboards commonly drive two chip-select pins to a memory stick. A single-ranked stick, will occupy only one of those rows. The other will be unused.

• Double-Ranked stick

A double-ranked stick has two chip-select rows which access different sets of memory devices. The two rows cannot be accessed concurrently.

• Double-sided stick

DEPRECATED TERM, see Double-Ranked stick.

A double-sided stick has two chip-select rows which access different sets of memory devices. The two rows cannot be accessed concurrently. “Double-sided” is irrespective of the memory devices being mounted on both sides of the memory stick.

• Socket set

All of the memory sticks that are required for a single memory access or all of the memory sticks spanned by a chip-select row. A single socket set has two chip-select rows and if double-sided sticks are used these will occupy those chip-select rows.

• Bank

This term is avoided because it is unclear when needing to distinguish between chip-select rows and socket sets.

• High Bandwidth Memory (HBM)

HBM is a new memory type with low power consumption and ultra-wide communication lanes. It uses vertically stacked memory chips (DRAM dies) interconnected by microscopic wires called “through-silicon vias,” or TSVs.

Several stacks of HBM chips connect to the CPU or GPU through an ultra-fast interconnect called the “interposer”. Therefore, HBM’s characteristics are nearly indistinguishable from on-chip integrated RAM.

Memory Controllers

Most of the EDAC core is focused on doing Memory Controller error detection. The edac_mc_alloc(). It uses internally the struct mem_ctl_info to describe the memory controllers, with is an opaque struct for the EDAC drivers. Only the EDAC core is allowed to touch it.

enum dev_type

describe the type of memory DRAM chips used at the stick

Constants

DEV_UNKNOWN

Can’t be determined, or MC doesn’t support detect it

DEV_X1

1 bit for data

DEV_X2

2 bits for data

DEV_X4

4 bits for data

DEV_X8

8 bits for data

DEV_X16

16 bits for data

DEV_X32

32 bits for data

DEV_X64

64 bits for data

Description

Typical values are x4 and x8.

enum hw_event_mc_err_type

type of the detected error

Constants

HW_EVENT_ERR_CORRECTED

Corrected Error - Indicates that an ECC corrected error was detected

HW_EVENT_ERR_UNCORRECTED

Uncorrected Error - Indicates an error that can’t be corrected by ECC, but it is not fatal (maybe it is on an unused memory area, or the memory controller could recover from it for example, by re-trying the operation).

HW_EVENT_ERR_DEFERRED

Deferred Error - Indicates an uncorrectable error whose handling is not urgent. This could be due to hardware data poisoning where the system can continue operation until the poisoned data is consumed. Preemptive measures may also be taken, e.g. offlining pages, etc.

HW_EVENT_ERR_FATAL

Fatal Error - Uncorrected error that could not be recovered.

HW_EVENT_ERR_INFO

Informational - The CPER spec defines a forth type of error: informational logs.

enum mem_type

memory types. For a more detailed reference, please see http://en.wikipedia.org/wiki/DRAM

Constants

MEM_EMPTY

Empty csrow

MEM_RESERVED

Reserved csrow type

MEM_UNKNOWN

Unknown csrow type

MEM_FPM

FPM - Fast Page Mode, used on systems up to 1995.

MEM_EDO

EDO - Extended data out, used on systems up to 1998.

MEM_BEDO

BEDO - Burst Extended data out, an EDO variant.

MEM_SDR

SDR - Single data rate SDRAM http://en.wikipedia.org/wiki/Synchronous_dynamic_random-access_memory They use 3 pins for chip select: Pins 0 and 2 are for rank 0; pins 1 and 3 are for rank 1, if the memory is dual-rank.

MEM_RDR

Registered SDR SDRAM

MEM_DDR

Double data rate SDRAM http://en.wikipedia.org/wiki/DDR_SDRAM

MEM_RDDR

Registered Double data rate SDRAM This is a variant of the DDR memories. A registered memory has a buffer inside it, hiding part of the memory details to the memory controller.

MEM_RMBS

Rambus DRAM, used on a few Pentium III/IV controllers.

MEM_DDR2

DDR2 RAM, as described at JEDEC JESD79-2F. Those memories are labeled as “PC2-” instead of “PC” to differentiate from DDR.

MEM_FB_DDR2

Fully-Buffered DDR2, as described at JEDEC Std No. 205 and JESD206. Those memories are accessed per DIMM slot, and not by a chip select signal.

MEM_RDDR2

Registered DDR2 RAM This is a variant of the DDR2 memories.

MEM_XDR

Rambus XDR It is an evolution of the original RAMBUS memories, created to compete with DDR2. Weren’t used on any x86 arch, but cell_edac PPC memory controller uses it.

MEM_DDR3

DDR3 RAM

MEM_RDDR3

Registered DDR3 RAM This is a variant of the DDR3 memories.

MEM_LRDDR3

Load-Reduced DDR3 memory.

MEM_LPDDR3

Low-Power DDR3 memory.

MEM_DDR4

Unbuffered DDR4 RAM

MEM_RDDR4

Registered DDR4 RAM This is a variant of the DDR4 memories.

MEM_LRDDR4

Load-Reduced DDR4 memory.

MEM_LPDDR4

Low-Power DDR4 memory.

MEM_DDR5

Unbuffered DDR5 RAM

MEM_RDDR5

Registered DDR5 RAM

MEM_LRDDR5

Load-Reduced DDR5 memory.

MEM_NVDIMM

Non-volatile RAM

MEM_WIO2

Wide I/O 2.

MEM_HBM2

High bandwidth Memory Gen 2.

MEM_HBM3

High bandwidth Memory Gen 3.

enum edac_type

Error Detection and Correction capabilities and mode

Constants

EDAC_UNKNOWN

Unknown if ECC is available

EDAC_NONE

Doesn’t support ECC

EDAC_RESERVED

Reserved ECC type

EDAC_PARITY

Detects parity errors

EDAC_EC

Error Checking - no correction

EDAC_SECDED

Single bit error correction, Double detection

EDAC_S2ECD2ED

Chipkill x2 devices - do these exist?

EDAC_S4ECD4ED

Chipkill x4 devices

EDAC_S8ECD8ED

Chipkill x8 devices

EDAC_S16ECD16ED

Chipkill x16 devices

enum scrub_type

scrubbing capabilities

Constants

SCRUB_UNKNOWN

Unknown if scrubber is available

SCRUB_NONE

No scrubber

SCRUB_SW_PROG

SW progressive (sequential) scrubbing

SCRUB_SW_SRC

Software scrub only errors

SCRUB_SW_PROG_SRC

Progressive software scrub from an error

SCRUB_SW_TUNABLE

Software scrub frequency is tunable

SCRUB_HW_PROG

HW progressive (sequential) scrubbing

SCRUB_HW_SRC

Hardware scrub only errors

SCRUB_HW_PROG_SRC

Progressive hardware scrub from an error

SCRUB_HW_TUNABLE

Hardware scrub frequency is tunable

enum edac_mc_layer_type

memory controller hierarchy layer

Constants

EDAC_MC_LAYER_BRANCH

memory layer is named “branch”

EDAC_MC_LAYER_CHANNEL

memory layer is named “channel”

EDAC_MC_LAYER_SLOT

memory layer is named “slot”

EDAC_MC_LAYER_CHIP_SELECT

memory layer is named “chip select”

EDAC_MC_LAYER_ALL_MEM

memory layout is unknown. All memory is mapped as a single memory area. This is used when retrieving errors from a firmware driven driver.

Description

This enum is used by the drivers to tell edac_mc_sysfs what name should be used when describing a memory stick location.

struct edac_mc_layer

describes the memory controller hierarchy

Definition:

struct edac_mc_layer {
    enum edac_mc_layer_type type;
    unsigned size;
    bool is_virt_csrow;
};

Members

type

layer type

size

number of components per layer. For example, if the channel layer has two channels, size = 2

is_virt_csrow

This layer is part of the “csrow” when old API compatibility mode is enabled. Otherwise, it is a channel

struct rank_info

contains the information for one DIMM rank

Definition:

struct rank_info {
    int chan_idx;
    struct csrow_info *csrow;
    struct dimm_info *dimm;
    u32 ce_count;
};

Members

chan_idx

channel number where the rank is (typically, 0 or 1)

csrow

A pointer to the chip select row structure (the parent structure). The location of the rank is given by the (csrow->csrow_idx, chan_idx) vector.

dimm

A pointer to the DIMM structure, where the DIMM label information is stored.

ce_count

number of correctable errors for this rank

Description

FIXME: Currently, the EDAC core model will assume one DIMM per rank.

This is a bad assumption, but it makes this patch easier. Later patches in this series will fix this issue.

struct edac_raw_error_desc

Raw error report structure

Definition:

struct edac_raw_error_desc {
    char location[LOCATION_SIZE];
    char label[(EDAC_MC_LABEL_LEN + 1 + sizeof(OTHER_LABEL)) * EDAC_MAX_LABELS];
    long grain;
    u16 error_count;
    enum hw_event_mc_err_type type;
    int top_layer;
    int mid_layer;
    int low_layer;
    unsigned long page_frame_number;
    unsigned long offset_in_page;
    unsigned long syndrome;
    const char *msg;
    const char *other_detail;
};

Members

location

location of the error

label

label of the affected DIMM(s)

grain

minimum granularity for an error report, in bytes

error_count

number of errors of the same type

type

severity of the error (CE/UE/Fatal)

top_layer

top layer of the error (layer[0])

mid_layer

middle layer of the error (layer[1])

low_layer

low layer of the error (layer[2])

page_frame_number

page where the error happened

offset_in_page

page offset

syndrome

syndrome of the error (or 0 if unknown or if the syndrome is not applicable)

msg

error message

other_detail

other driver-specific detail about the error

struct dimm_info *edac_get_dimm(struct mem_ctl_info *mci, int layer0, int layer1, int layer2)

Get DIMM info from a memory controller given by [layer0,layer1,layer2] position

Parameters

struct mem_ctl_info *mci

MC descriptor struct mem_ctl_info

int layer0

layer0 position

int layer1

layer1 position. Unused if n_layers < 2

int layer2

layer2 position. Unused if n_layers < 3

Description

For 1 layer, this function returns “dimms[layer0]”;

For 2 layers, this function is similar to allocating a two-dimensional array and returning “dimms[layer0][layer1]”;

For 3 layers, this function is similar to allocating a tri-dimensional array and returning “dimms[layer0][layer1][layer2]”;

struct mem_ctl_info *edac_mc_alloc(unsigned int mc_num, unsigned int n_layers, struct edac_mc_layer *layers, unsigned int sz_pvt)

Allocate and partially fill a struct mem_ctl_info.

Parameters

unsigned int mc_num

Memory controller number

unsigned int n_layers

Number of MC hierarchy layers

struct edac_mc_layer *layers

Describes each layer as seen by the Memory Controller

unsigned int sz_pvt

size of private storage needed

Description

Everything is kmalloc’ed as one big chunk - more efficient. Only can be used if all structures have the same lifetime - otherwise you have to allocate and initialize your own structures.

Use edac_mc_free() to free mc structures allocated by this function.

Note

drivers handle multi-rank memories in different ways: in some drivers, one multi-rank memory stick is mapped as one entry, while, in others, a single multi-rank memory stick would be mapped into several entries. Currently, this function will allocate multiple struct dimm_info on such scenarios, as grouping the multiple ranks require drivers change.

Return

On success, return a pointer to struct mem_ctl_info pointer; NULL otherwise

const char *edac_get_owner(void)

Return the owner’s mod_name of EDAC MC

Parameters

void

no arguments

Return

Pointer to mod_name string when EDAC MC is owned. NULL otherwise.

void edac_mc_free(struct mem_ctl_info *mci)

Frees a previously allocated mci structure

Parameters

struct mem_ctl_info *mci

pointer to a struct mem_ctl_info structure

bool edac_has_mcs(void)

Check if any MCs have been allocated.

Parameters

void

no arguments

Return

True if MC instances have been registered successfully. False otherwise.

struct mem_ctl_info *edac_mc_find(int idx)

Search for a mem_ctl_info structure whose index is idx.

Parameters

int idx

index to be seek

Description

If found, return a pointer to the structure. Else return NULL.

struct mem_ctl_info *find_mci_by_dev(struct device *dev)

Scan list of controllers looking for the one that manages the dev device.

Parameters

struct device *dev

pointer to a struct device related with the MCI

Return

on success, returns a pointer to struct mem_ctl_info; NULL otherwise.

struct mem_ctl_info *edac_mc_del_mc(struct device *dev)

Remove sysfs entries for mci structure associated with dev and remove mci structure from global list.

Parameters

struct device *dev

Pointer to struct device representing mci structure to remove.

Return

pointer to removed mci structure, or NULL if device not found.

int edac_mc_find_csrow_by_page(struct mem_ctl_info *mci, unsigned long page)

Ancillary routine to identify what csrow contains a memory page.

Parameters

struct mem_ctl_info *mci

pointer to a struct mem_ctl_info structure

unsigned long page

memory page to find

Return

on success, returns the csrow. -1 if not found.

void edac_raw_mc_handle_error(struct edac_raw_error_desc *e)

Reports a memory event to userspace without doing anything to discover the error location.

Parameters

struct edac_raw_error_desc *e

error description

Description

This raw function is used internally by edac_mc_handle_error(). It should only be called directly when the hardware error come directly from BIOS, like in the case of APEI GHES driver.

void edac_mc_handle_error(const enum hw_event_mc_err_type type, struct mem_ctl_info *mci, const u16 error_count, const unsigned long page_frame_number, const unsigned long offset_in_page, const unsigned long syndrome, const int top_layer, const int mid_layer, const int low_layer, const char *msg, const char *other_detail)

Reports a memory event to userspace.

Parameters

const enum hw_event_mc_err_type type

severity of the error (CE/UE/Fatal)

struct mem_ctl_info *mci

a struct mem_ctl_info pointer

const u16 error_count

Number of errors of the same type

const unsigned long page_frame_number

mem page where the error occurred

const unsigned long offset_in_page

offset of the error inside the page

const unsigned long syndrome

ECC syndrome

const int top_layer

Memory layer[0] position

const int mid_layer

Memory layer[1] position

const int low_layer

Memory layer[2] position

const char *msg

Message meaningful to the end users that explains the event

const char *other_detail

Technical details about the event that may help hardware manufacturers and EDAC developers to analyse the event

PCI Controllers

The EDAC subsystem provides a mechanism to handle PCI controllers by calling the edac_pci_alloc_ctl_info(). It will use the struct edac_pci_ctl_info to describe the PCI controllers.

struct edac_pci_ctl_info *edac_pci_alloc_ctl_info(unsigned int sz_pvt, const char *edac_pci_name)

The alloc() function for the ‘edac_pci’ control info structure.

Parameters

unsigned int sz_pvt

size of the private info at struct edac_pci_ctl_info

const char *edac_pci_name

name of the PCI device

Description

The chip driver will allocate one of these for each edac_pci it is going to control/register with the EDAC CORE.

Return

a pointer to struct edac_pci_ctl_info on success; NULL otherwise.

void edac_pci_free_ctl_info(struct edac_pci_ctl_info *pci)

Last action on the pci control structure.

Parameters

struct edac_pci_ctl_info *pci

pointer to struct edac_pci_ctl_info

Description

Calls the remove sysfs information, which will unregister this control struct’s kobj. When that kobj’s ref count goes to zero, its release function will be call and then kfree() the memory.

int edac_pci_alloc_index(void)

Allocate a unique PCI index number

Parameters

void

no arguments

Return

allocated index number

int edac_pci_add_device(struct edac_pci_ctl_info *pci, int edac_idx)

Insert the ‘edac_dev’ structure into the edac_pci global list and create sysfs entries associated with edac_pci structure.

Parameters

struct edac_pci_ctl_info *pci

pointer to the edac_device structure to be added to the list

int edac_idx

A unique numeric identifier to be assigned to the ‘edac_pci’ structure.

Return

0 on Success, or an error code on failure

struct edac_pci_ctl_info *edac_pci_del_device(struct device *dev)

Parameters

struct device *dev

Pointer to ‘struct device’ representing edac_pci structure to remove

Description

Remove sysfs entries for specified edac_pci structure and then remove edac_pci structure from global list

Return

Pointer to removed edac_pci structure, or NULL if device not found

struct edac_pci_ctl_info *edac_pci_create_generic_ctl(struct device *dev, const char *mod_name)

Parameters

struct device *dev

pointer to struct device;

const char *mod_name

name of the PCI device

Description

A generic constructor for a PCI parity polling device Some systems have more than one domain of PCI busses. For systems with one domain, then this API will provide for a generic poller.

This routine calls the edac_pci_alloc_ctl_info() for the generic device, with default values

Return

Pointer to struct edac_pci_ctl_info on success, NULL on

failure.

void edac_pci_release_generic_ctl(struct edac_pci_ctl_info *pci)

Parameters

struct edac_pci_ctl_info *pci

pointer to struct edac_pci_ctl_info

Description

The release function of a generic EDAC PCI polling device

int edac_pci_create_sysfs(struct edac_pci_ctl_info *pci)

Parameters

struct edac_pci_ctl_info *pci

pointer to struct edac_pci_ctl_info

Description

Create the controls/attributes for the specified EDAC PCI device

void edac_pci_remove_sysfs(struct edac_pci_ctl_info *pci)

Parameters

struct edac_pci_ctl_info *pci

pointer to struct edac_pci_ctl_info

Description

remove the controls and attributes for this EDAC PCI device

EDAC Blocks

The EDAC subsystem also provides a generic mechanism to report errors on other parts of the hardware via edac_device_alloc_ctl_info() function.

The structures edac_dev_sysfs_block_attribute, edac_device_block, edac_device_instance and edac_device_ctl_info provide a generic or abstract ‘edac_device’ representation at sysfs.

This set of structures and the code that implements the APIs for the same, provide for registering EDAC type devices which are NOT standard memory or PCI, like:

• CPU caches (L1 and L2)

• DMA engines

• Core CPU switches

• Fabric switch units

• PCIe interface controllers

• other EDAC/ECC type devices that can be monitored for errors, etc.

It allows for a 2 level set of hierarchy.

For example, a cache could be composed of L1, L2 and L3 levels of cache. Each CPU core would have its own L1 cache, while sharing L2 and maybe L3 caches. On such case, those can be represented via the following sysfs nodes:

/sys/devices/system/edac/..

pci/            <existing pci directory (if available)>
mc/             <existing memory device directory>
cpu/cpu0/..     <L1 and L2 block directory>
        /L1-cache/ce_count
                 /ue_count
        /L2-cache/ce_count
                 /ue_count
cpu/cpu1/..     <L1 and L2 block directory>
        /L1-cache/ce_count
                 /ue_count
        /L2-cache/ce_count
                 /ue_count
...

the L1 and L2 directories would be "edac_device_block's"

int edac_device_add_device(struct edac_device_ctl_info *edac_dev)

Insert the ‘edac_dev’ structure into the edac_device global list and create sysfs entries associated with edac_device structure.

Parameters

struct edac_device_ctl_info *edac_dev

pointer to edac_device structure to be added to the list ‘edac_device’ structure.

Return

0 on Success, or an error code on failure

struct edac_device_ctl_info *edac_device_del_device(struct device *dev)

Remove sysfs entries for specified edac_device structure and then remove edac_device structure from global list

Parameters

struct device *dev

Pointer to struct device representing the edac device structure to remove.

Return

Pointer to removed edac_device structure, or NULL if device not found.

void edac_device_handle_ce_count(struct edac_device_ctl_info *edac_dev, unsigned int count, int inst_nr, int block_nr, const char *msg)

Log correctable errors.

Parameters

struct edac_device_ctl_info *edac_dev

pointer to struct edac_device_ctl_info

unsigned int count

Number of errors to log.

int inst_nr

number of the instance where the CE error happened

int block_nr

number of the block where the CE error happened

const char *msg

message to be printed

void edac_device_handle_ue_count(struct edac_device_ctl_info *edac_dev, unsigned int count, int inst_nr, int block_nr, const char *msg)

Log uncorrectable errors.

Parameters

struct edac_device_ctl_info *edac_dev

pointer to struct edac_device_ctl_info

unsigned int count

Number of errors to log.

int inst_nr

number of the instance where the CE error happened

int block_nr

number of the block where the CE error happened

const char *msg

message to be printed

void edac_device_handle_ce(struct edac_device_ctl_info *edac_dev, int inst_nr, int block_nr, const char *msg)

Log a single correctable error

Parameters

struct edac_device_ctl_info *edac_dev

pointer to struct edac_device_ctl_info

int inst_nr

number of the instance where the CE error happened

int block_nr

number of the block where the CE error happened

const char *msg

message to be printed

void edac_device_handle_ue(struct edac_device_ctl_info *edac_dev, int inst_nr, int block_nr, const char *msg)

Log a single uncorrectable error

Parameters

struct edac_device_ctl_info *edac_dev

pointer to struct edac_device_ctl_info

int inst_nr

number of the instance where the UE error happened

int block_nr

number of the block where the UE error happened

const char *msg

message to be printed

int edac_device_alloc_index(void)

Allocate a unique device index number

Parameters

void

no arguments

Return

allocated index number

Heterogeneous system support

An AMD heterogeneous system is built by connecting the data fabrics of both CPUs and GPUs via custom xGMI links. Thus, the data fabric on the GPU nodes can be accessed the same way as the data fabric on CPU nodes.

The MI200 accelerators are data center GPUs. They have 2 data fabrics, and each GPU data fabric contains four Unified Memory Controllers (UMC). Each UMC contains eight channels. Each UMC channel controls one 128-bit HBM2e (2GB) channel (equivalent to 8 X 2GB ranks). This creates a total of 4096-bits of DRAM data bus.

While the UMC is interfacing a 16GB (8high X 2GB DRAM) HBM stack, each UMC channel is interfacing 2GB of DRAM (represented as rank).

Memory controllers on AMD GPU nodes can be represented in EDAC thusly:

GPU DF / GPU Node -> EDAC MC GPU UMC -> EDAC CSROW GPU UMC channel -> EDAC CHANNEL

For example: a heterogeneous system with 1 AMD CPU is connected to 4 MI200 (Aldebaran) GPUs using xGMI.

Some more heterogeneous hardware details:

• The CPU UMC (Unified Memory Controller) is mostly the same as the GPU UMC. They have chip selects (csrows) and channels. However, the layouts are different for performance, physical layout, or other reasons.

• CPU UMCs use 1 channel, In this case UMC = EDAC channel. This follows the marketing speak. CPU has X memory channels, etc.

• CPU UMCs use up to 4 chip selects, So UMC chip select = EDAC CSROW.

• GPU UMCs use 1 chip select, So UMC = EDAC CSROW.

• GPU UMCs use 8 channels, So UMC channel = EDAC channel.

The EDAC subsystem provides a mechanism to handle AMD heterogeneous systems by calling system specific ops for both CPUs and GPUs.

AMD GPU nodes are enumerated in sequential order based on the PCI hierarchy, and the first GPU node is assumed to have a Node ID value following those of the CPU nodes after latter are fully populated:

$ ls /sys/devices/system/edac/mc/
        mc0   - CPU MC node 0
        mc1  |
        mc2  |- GPU card[0] => node 0(mc1), node 1(mc2)
        mc3  |
        mc4  |- GPU card[1] => node 0(mc3), node 1(mc4)
        mc5  |
        mc6  |- GPU card[2] => node 0(mc5), node 1(mc6)
        mc7  |
        mc8  |- GPU card[3] => node 0(mc7), node 1(mc8)

For example, a heterogeneous system with one AMD CPU is connected to four MI200 (Aldebaran) GPUs using xGMI. This topology can be represented via the following sysfs entries:

/sys/devices/system/edac/mc/..

CPU                     # CPU node
├── mc 0

GPU Nodes are enumerated sequentially after CPU nodes have been populated
GPU card 1              # Each MI200 GPU has 2 nodes/mcs
├── mc 1                # GPU node 0 == mc1, Each MC node has 4 UMCs/CSROWs
│   ├── csrow 0         # UMC 0
│   │   ├── channel 0   # Each UMC has 8 channels
│   │   ├── channel 1   # size of each channel is 2 GB, so each UMC has 16 GB
│   │   ├── channel 2
│   │   ├── channel 3
│   │   ├── channel 4
│   │   ├── channel 5
│   │   ├── channel 6
│   │   ├── channel 7
│   ├── csrow 1         # UMC 1
│   │   ├── channel 0
│   │   ├── ..
│   │   ├── channel 7
│   ├── ..              ..
│   ├── csrow 3         # UMC 3
│   │   ├── channel 0
│   │   ├── ..
│   │   ├── channel 7
│   ├── rank 0
│   ├── ..              ..
│   ├── rank 31         # total 32 ranks/dimms from 4 UMCs
├
├── mc 2                # GPU node 1 == mc2
│   ├── ..              # each GPU has total 64 GB

GPU card 2
├── mc 3
│   ├── ..
├── mc 4
│   ├── ..

GPU card 3
├── mc 5
│   ├── ..
├── mc 6
│   ├── ..

GPU card 4
├── mc 7
│   ├── ..
├── mc 8
│   ├── ..