docs/bindings/vendor-ibm-astlpc.md

18 …<https://www.intel.com/content/dam/www/program/design/us/en/documents/low-pin-count-interface-spec…
29 MCTP-compliant endpoints must accept.
33 A hardware-defined flag bit in a KCS device's Status Register (STR). The IBF
42 ### KCS: Keyboard-Controller-Style
48 systems. This interface is available built-in to several commercially available
49 microcontrollers. Data is transferred across the KCS interface using a per-byte
68 values larger than the BTU may improve throughput for data-intensive transfers.
72 A hardware-defined flag bit in a KCS device's Status Register (STR). The OBF
84 BMC-controlled, eight-bit register exposed to both the BMC and the host for
86 Bits that are not defined by hardware can be software-controlled in a manner
87 defined by a platform-specific ABI.
100 - An interrupt mechanism using the IPMI KCS interface
101 - A window of the LPC FW address space, where reads and writes are forwarded to
107    - The BMC will perform writes by writing to the memory backing the LPC window
108    - The host will perform writes by writing to the LPC bus, at predefined
114 1. Read from the KCS status register, which shows that the single-byte KCS data
134 The KCS hardware consists of two single-byte buffers: the Output Data Register
139 to determine if there is data in the ODR or IDR. These are single-bit flags,
145 software-defined bits in the status register are used to carry other required
150 buffer-full flag and invoke an interrupt.
158 The window of BMC-memory-backed LPC FW address space has a predefined format,
161 - A control descriptor, describing static data about the rest of the window
162 - A receive area for BMC-to-host packets
163 - A transmit area, for host-to-BMC packets
197 All medium-specific metadata is in big-endian format. This includes:
200 2. Medium-specific packet header fields
201 3. Medium-specific packet trailer fields
207 medium-specific header comprising a 32-bit payload length field, followed
218 A medium-specific packet trailer must immediately follow the payload. The length
219 of the trailer is not accounted for in the length field of the medium-specific
223 For protocol versions 1 and 2, the medium-specific trailer length is zero.
225 For protocol version 3, the medium-specific trailer comprises a CRC-32 checksum
234 Where the CRC-32 implementation is defined by the following characteristics (or
239 2. Initialising the remainder state to `2^32 - 1`
242 4. `XOR`ing the calculated remainder with `2^32 - 1`
257 necessarily backwards-compatible.
275 - Intersect neither eachother nor the control region
276 - Not extend beyond the window allocated to MCTP in the LPC FW address space
277 - Must accommodate at least BTU-sized payloads
290 | ------- | ---------- | ---------------------------------- |
303 | ------- | ----------- |
315 | ---- | ------------------------------------------------------- |
328 | ---- | ------------------------------------------------------- |
341 | ---- | -------------------------------------------------------------- |
357 - The control data is only written during initialisation. The control area is
359 - Only the BMC may write to the Rx buffer described in the control area
360 - Only the host may write to the Tx buffer described in the control area
380 [KCS Control](#kcs-control).
388 | ---- | ------------------------------------------------------------------------------------- |
395 | ---- | --- | --- | --- | ------------------------------------------------------------------------…
411 | ---- | --- | --- | --- | ------------------------------------------------------------------------…
412 | 1    |     |     | ✓   | The host calculates the CRC-32 over the packet data                     …
414 | 3    | ✓   | ✓   | ✓   | The host writes the packet data and medium-specific metadata to its Tx a…
417 | 6    | ✓   | ✓   | ✓   | The BMC reads the packet data and medium-specific metadata from the its …
420 | 9    |     |     | ✓   | The BMC validates the provided CRC-32 over the packet data              …
425 | ---- | --- | --- | --- | ------------------------------------------------------------------------…
426 | 1    |     |     | ✓   | The BMC calculates the CRC-32 over the packet data                      …
428 | 3    | ✓   | ✓   | ✓   | The BMC writes the packet data and medium-specific metadata to its Tx ar…
431 | 6    | ✓   | ✓   | ✓   | The host reads the packet data and medium-specific metadata from the hos…
434 | 9    |     |     | ✓   | The host validates the provided CRC-32 over the packet data             …
441 - An LPC KCS device exposed by a [binding-specific kernel driver][mctp-driver]
442 - The reserved memory mapped by the LPC2AHB bridge via the [aspeed-lpc-ctrl
443   driver][aspeed-lpc-ctrl]
444 - The astlpc binding found in [libmctp][libmctp]
446 [mctp-driver]:
448 [aspeed-lpc-ctrl]:
449 …el.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/soc/aspeed/aspeed-lpc-ctrl.c?h=v5.7
453 free-standing firmware. Some firmwares exploit [libmctp][libmctp] by
461 arbitrarily-sized MCTP messages. However, there are much larger overheads in
469 the complexity introduced would make low-level debugging both more difficult and
474 The BT interface allows for block-at-time transfers. However, the BT buffer size
476 the MCTP Base Specification (DSP0236) that requires a 64-byte payload size as
477 the minimum. The 64-byte BT buffer does not allow for MCTP and transport