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diff --git a/Documentation/superio/common/pnp.md b/Documentation/superio/common/pnp.md new file mode 100644 index 0000000000..314cac27ed --- /dev/null +++ b/Documentation/superio/common/pnp.md @@ -0,0 +1,114 @@ +# PNP devices + +Typical PNP devices are Super I/Os, LPC-connected TPMs and board +management controllers. + +PNP devices are usually connected to the LPC or eSPI bus of a system +and shouldn't be confused with PCI(e) devices that use a completely +different plug and play mechanism. PNP originates in the ISA plug and +play specification. Since the original ISA bus is more or less extinct, +the auto-detection part of ISA PNP is mostly irrelevant nowadays. For +the register offsets for different functionality, appendix A of that +specification is still the main reference though. + +## Configuration access and config mode + +Super I/O chips connected via LPC to the southbridge usually have their +I/O-mapped configuration interface with a size of two bytes at the base +address 0x2e or 0x4e. Other PNP devices have their configuration +interface at other addresses. + +The two byte registers allow access to an indirect 256 bytes big +register space that contains the configuration. By writing the index +to the lower byte (e.g. 0x2e), you can access the register contents at +that index by reading/writing the higher byte (e.g. 0x2f). + +To prevent accidental changes of the Super I/O (SIO) configuration, +the SIOs need a configuration mode unlock sequence. After changing the +configuration, the configuration mode should be left again, by sending +the configuration mode lock sequence. + +## Logical device numbers (LDN) + +Each PNP device can contain multiple logical devices. The bytes from +0x00 to 0x2f in the indirect configuration register space are common +for all LDNs, but some SIO chips require a certain LDN to be selected +in order to write certain registers in there. An LDN gets selected by +writing the LDN number to the LDN select register 0x07. Registers 0x30 +to 0xFF are specific to each LDN number. + +coreboot encodes the physical LDN number in the lower byte of the LDN +number. + +### Virtual logical device numbers + +Register 0x30 is the LDN enable register and since it is an 8 bit +register, it can contain up to 8 enable bits for different parts of +the functionality of that logical device. To set a certain enable bit +in one physical LDN, the concept of virtual LDNs was introduced. +Virtual LDNs share the registers of their base LDN, but allow to +specify which part of a LDN should be enabled. + +coreboot encodes the enable bit number and by that the virtual LDN +part in the lower 3 bits of the higher byte of the LDN number. + +## I/O resources + +Starting at register address 0x60, each LDN has 2 byte wide I/O base +address registers. The size of an I/O resource is always a power of +two. + +### I/O resource masks + +The I/O resource masks encode both the size and the maximum base +address of the corresponding IO resource. The number of zeros counted +from the least significant bit encode the resource size. If N is the +number of LSBs being zero, which can also be zero if the LSB is a one, +the resource has N address bits and a size of 2\*\*N bytes. The mask +address is also the highest possible address to map the I/O region. + +A typical example for an I/O resource mask is 0x07f8 which is +0b0000011111111000 in binary notation. The three LSBs are zeros here, +so it's an eight byte I/O resource with three address offset bits +inside the resource. The highest base address it can be mapped to is +0x07f8, so the region will end at 0x07ff. + +The Super I/O datasheets typically contain the information about the +I/O resource masks. On most Super I/O chips the mask can also be found +out by writing 0xffff to the corresponding I/O base address register +and reading back the value; since the lowest and highest bits are +hard-wired to zero according to the I/O resource size and maximal +possible I/O address, this gives the mask. + +## IRQ resources + +Each physical LDN has up to two configurable interrupt request +register pairs 0x70, 0x71 and 0x72, 0x73. Each pair can be configured +to use a certain IRQ number. Writing 1 to 15 into the first register +selects the IRQ number generated by the corresponding IRQ source and +enables IRQ generation; writing 0 to it disables the generation of +IRQs for the source. The second register selects the IRQ type (level +or edge) and IRQ level (high or low). For LPC SIOs the IRQ type is +hard-wired to edge. + +On the LPC bus a shared SERIRQ line is used to signal IRQs to the +host; the IRQ number gets encoded by the number of LPC clock cycles +after the start frame before the device pulls the open drain +connection low. + +SERIRQ can be used in two different modes: In the continuous SERIRQ +mode the host continuously sends IRQ frame starts and the devices +signal their IRQ request by pulling low the SERIRQ line at the right +time. In quiet SERIRQ mode the host doesn't send IRQ frame starts, so +the devices have to send both the IRQ frame start and the encoded IRQ +number. The quiet mode is often broken. + +## DRQ resources + +Each physical LDN has two legacy ISA-style DMA request channel +registers at 0x74 and 0x75. Those are only used for legacy devices +like parallel printer ports or floppy disk controllers. + +Each device using LPC legacy DMA needs its own LDMA line to the host. +Some newer chipsets have dropped the LDMA line and with that the +legacy DMA capability on LPC. diff --git a/Documentation/superio/index.md b/Documentation/superio/index.md index 39965fde07..053663b215 100644 --- a/Documentation/superio/index.md +++ b/Documentation/superio/index.md @@ -7,4 +7,5 @@ This section contains documentation about coreboot on specific SuperIOs. - [NPCD378](nuvoton/npcd378.md) ## Common +- [PNP devices](common/pnp.md) - [SSDT generator for generic SuperIOs](common/ssdt.md) |