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.
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.
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).
A physical connector on the motherboard that accepts a single memory
stick. Also called as “slot” on several datasheets.
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.
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.
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.
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.
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.
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.
A double-ranked stick has two chip-select rows which access different
sets of memory devices. The two rows cannot be accessed concurrently.
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.
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.
This term is avoided because it is unclear when needing to distinguish
between chip-select rows and socket sets.
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_DDR4
- Unbuffered DDR4 RAM
- MEM_RDDR4
- Registered DDR4 RAM
This is a variant of the DDR4 memories.
- MEM_LRDDR4
- Load-Reduced DDR4 memory.
-
enum edac_type
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
-
EDAC_DIMM_OFF(layers, nlayers, layer0, layer1, layer2)
Macro responsible to get a pointer offset inside a pointer array for the element given by [layer0,layer1,layer2] position
Parameters
- layers
- a struct edac_mc_layer array, describing how many elements
were allocated for each layer
- nlayers
- Number of layers at the layers array
- layer0
- layer0 position
- layer1
- layer1 position. Unused if n_layers < 2
- layer2
- layer2 position. Unused if n_layers < 3
Description
For 1 layer, this macro returns “var[layer0] - var”;
For 2 layers, this macro is similar to allocate a bi-dimensional array
and to return “var[layer0][layer1] - var”;
For 3 layers, this macro is similar to allocate a tri-dimensional array
and to return “var[layer0][layer1][layer2] - var”.
A loop could be used here to make it more generic, but, as we only have
3 layers, this is a little faster.
By design, layers can never be 0 or more than 3. If that ever happens,
a NULL is returned, causing an OOPS during the memory allocation routine,
with would point to the developer that he’s doing something wrong.
-
EDAC_DIMM_PTR(layers, var, nlayers, layer0, layer1, layer2)
Macro responsible to get a pointer inside a pointer array for the element given by [layer0,layer1,layer2] position
Parameters
- layers
- a struct edac_mc_layer array, describing how many elements
were allocated for each layer
- var
- name of the var where we want to get the pointer
(like mci->dimms)
- nlayers
- Number of layers at the layers array
- layer0
- layer0 position
- layer1
- layer1 position. Unused if n_layers < 2
- layer2
- layer2 position. Unused if n_layers < 3
Description
For 1 layer, this macro returns “var[layer0]”;
For 2 layers, this macro is similar to allocate a bi-dimensional array
and to return “var[layer0][layer1]”;
For 3 layers, this macro is similar to allocate a tri-dimensional array
and to return “var[layer0][layer1][layer2]”;
-
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;
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;
bool enable_per_layer_report;
};
Members
- location[LOCATION_SIZE]
- location of the error
- label[(EDAC_MC_LABEL_LEN + 1 + sizeof(OTHER_LABEL)) *EDAC_MAX_LABELS]
- label of the affected DIMM(s)
- grain
- minimum granularity for an error report, in bytes
- error_count
- number of errors of the same type
- 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
- enable_per_layer_report
- if false, the error affects all layers
(typically, a memory controller error)
-
struct mem_ctl_info * edac_mc_alloc(unsigned mc_num, unsigned n_layers, struct edac_mc_layer * layers, unsigned sz_pvt)
Allocate and partially fill a struct mem_ctl_info.
Parameters
- unsigned mc_num
- Memory controller number
- unsigned n_layers
- Number of MC hierarchy layers
- struct edac_mc_layer * layers
- Describes each layer as seen by the Memory Controller
- unsigned 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
-
int edac_mc_add_mc_with_groups(struct mem_ctl_info * mci, const struct attribute_group ** groups)
Insert the mci structure into the mci global list and create sysfs entries associated with mci structure.
Parameters
- struct mem_ctl_info * mci
- pointer to the mci structure to be added to the list
- const struct attribute_group ** groups
- optional attribute groups for the driver-specific sysfs entries
Return
0 on Success, or an error code on failure
-
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(const enum hw_event_mc_err_type type, struct mem_ctl_info * mci, struct edac_raw_error_desc * e)
Reports a memory event to userspace without doing anything to discover the error location.
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
- 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)
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 alloc() function for the ‘edac_pci’ control info
structure.
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)
Parameters
- struct edac_pci_ctl_info * pci
- pointer to struct edac_pci_ctl_info
Description
Last action on the pci control structure.
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)
Parameters
- void
- no arguments
Return
allocated index number
-
int edac_pci_add_device(struct edac_pci_ctl_info * pci, int edac_idx)
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.
Description
edac_pci global list and create sysfs entries associated with
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)
Parameters
- struct edac_device_ctl_info * edac_dev
- pointer to edac_device structure to be added to the list
‘edac_device’ structure.
Description
edac_device global list and create sysfs entries associated with
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)
Parameters
- struct device * dev
- Pointer to struct device representing the edac device
structure to remove.
Description
Remove sysfs entries for specified edac_device structure and
then remove edac_device structure from global list
Return
Pointer to removed edac_device structure,
or NULL if device not found.
-
void edac_device_handle_ue(struct edac_device_ctl_info * edac_dev, int inst_nr, int block_nr, const char * msg)
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
Description
perform a common output and handling of an ‘edac_dev’ UE event
-
void edac_device_handle_ce(struct edac_device_ctl_info * edac_dev, int inst_nr, int block_nr, const char * msg)
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
Description
perform a common output and handling of an ‘edac_dev’ CE event
-
int edac_device_alloc_index(void)
Parameters
- void
- no arguments
Return
allocated index number