Developer Manual/Super IO

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The Super I/O is a chip found on most of today's mainboards which is — among other things — responsible for the serial ports of the mainboard (e.g. COM1, COM2). This chip is usually the first thing you'll want to support, as it's required to get serial debugging output from the mainboard (via a null-modem cable and the proper software, e.g. minicom or CuteCom).

Winbond W83977EF Super I/O
ITE IT8705F Super I/O


Logical Devices (LDN)

Every Super I/O chip provides different kinds of functions to the computer, such as control over GPIOs, GAME port, MIDI port, fan controllers, infrared and more.

Each of these functions, inside a Super I/O, is split into its own logical device and everyone of these devices is identified by an hex number (starting from 0x0) called logical device number (LDN). I.e. In some Super I/Os, like the IT8728F, 0x05 and 0x06 are the LDNs respectively for the keyboard and the mouse.

Check your chip's datasheet to find the complete list.

Configuration registers

A Super I/O chip can be configured through the use of its configuration registers.

These registers can be divided into two classes:

  • Super I/O control and configuration
  • Logical Device control and configuration

The first class contains all the registers that have the same value no matter which LDN has been selected, a sort of "global" register. An example of this class can be found in the LDN register (reg 0x7) which is used to select an LDN, the Super I/O ID register (reg 0x20) and the Revision ID register (reg 0x27) which contain respectively the ID and the revision number of your chip.

The second class includes all the registers that are relative to the LDN that has been previously selected. Among these ones there is the Logical Device Control register (reg 0x30) which is used to enable or disable the functionality of that Logical Device, the I/O Address register (reg 0x60-0x61) which are used to access runtime registers, and others.

Access by Index and Data

In order to access any configuration register you'll have to use two special registers:

  • Index register (I/O port 0x2E or 0x4E, depending on the chip)
  • Data register (I/O port 0x2F or 0x4F, obtained by adding 1 to the Index register)

The Index register is used to specify which of the configuration registers you want to access. This is accomplished by writing a byte containing the desired register's number into the Index register.

The Data register is used to read or write a byte of data from/into the register pointed to by the Index register.

The next examples should clarify the configuration process.

  I.e. how to read the chip's index
  
  outb(0x20, index_reg); // Points the Index register to the ID register (reg 0x20)
  int id = inb(data_reg); // Reads the ID value from the Data register and stores it
  
  I.e. how to select a logical device
  
  outb(0x07, index_reg); // Points the Index register to the LDN register (0x07)
  outb(0x03, data_reg); // Selects the LDN 0x03
  
  I.e. how to enable a logical device (You have to first select a logical device)
  
  outb(0x30, index_reg); // Points the Index register to the logical device control register (0x30)
  outb(0x01, data_reg); // Turns on the first bit of the logical device control register

Virtual Logical Device Number (vLDN)

Some Super I/O's use register 0x30 of one of the logical device numbers (LDN) to also enable other logical device's functions. For example, in the case of the W83627EHF chip, register 0x30 of LDN 0x9 was used to enable multiple devices (GPIO2 = bit0, GPIO3 = bit1, GPIO4 = bit2 and GPIO5 = bit3). To overcome this issue a concept of virtual LDN has been introduced.

Virtual LDN's can be used in Coreboot to uniquely map the enable bit position in register 0x30 of an LDN, this allows to use a general way to handle any bit enable operation required without special cases.

Originally, except in cases such as the W83627EHF's, to enable or disable an LDN's functionality you only had to just switch on or off bit0 of the register 0x30, however a virtual LDN is created as follows:

  • Low [7:0] bits are used to describe the original LDN.
  • High [10:8] bits select the position of the bit enable in the register 0x30.

Note: the bit positions are in hex.

I.e. W83627EHF chip

In order to enable the GPIO5 (bit3 of register 0x30) this is what the virtual LDN has to look like this:

  [0000 0011] [0000 1001] = 0x309
   ^^^^^^^^^   ^^^^^^^^^
        |          |
        |          +------- Original LDN
        |
        |
        +------- Position inside register 0x30


Note: if the virtual LDN is 0x7 it will handle bit0 of register 0x30.

Super I/O bring-up

Adding support for a new Super I/O chip is usually not significantly hard once you have obtained the datasheet for your target chip. Herein we shall outline the steps usually taken for a bring-up.

Source layout

Create the top-level directory src/superio/vendor/device (e.g. src/superio/winbond/w83627ehg). Within src/superio/vendor edit both Kconfig and Makefile.inc the changes will be self-evident. All super i/o support is then contained in src/superio/vendor/device, we provide here the minimum of a usual bringup.

Makefile.inc

The src/superio/vendor/device/Makefile.inc should contain the following two lines:

 romstage-$(CONFIG_SUPERIO_VENDOR_DEVICE) += early_serial.c
 ramstage-$(CONFIG_SUPERIO_VENDOR_DEVICE) += superio.c

Obviously replacing VENDOR and DEVICE respectively.

device.h, (e.g., w83627ehg.h)

The src/superio/vendor/device/device.h header should contain the Super I/O supported Logical Device Numbers (LDN) and the early_serial enabling function prototype.

For example, for f71869ad.h we have:

 #ifndef SUPERIO_FINTEK_F71869AD_F71869AD_H
 #define SUPERIO_FINTEK_F71869AD_F71869AD_H
 
 /* Logical Device Numbers (LDN). */
 #define F71869AD_FDC  0x00      /* Floppy */
 #define F71869AD_SP1  0x01      /* UART1 */
 #define F71869AD_SP2  0x02      /* UART2 */
 #define F71869AD_PP   0x03      /* Parallel port */
 #define F71869AD_HWM  0x04      /* Hardware monitor */
 #define F71869AD_KBC  0x05      /* PS/2 keyboard and mouse */
 #define F71869AD_GPIO 0x06      /* General Purpose I/O (GPIO) */
 #define F71869AD_BSEL 0x07      /* BSEL */
 #define F71869AD_PME  0x0a      /* Power Management Events (PME) and ACPI */
 
 void f71869ad_enable_serial(device_t dev, u16 iobase);
 
 #endif /* SUPERIO_FINTEK_F71869AD_F71869AD_H */

You can find out what LDN's your chip has from its data-sheet LDN summary table.

early_serial.c

The src/superio/vendor/device/early_serial.c file will be responsible to setup a serial port on the mainboard as to get serial debugging output. N.B. This will work even before the RAM is initialized, thus is useful/required for debugging the RAM initialization process. In this file you now declare a function device_enable_serial() which enables the requested serial port. For example:

 void w83627ehg_enable_serial(device_t dev, unsigned int iobase)
 {
        pnp_enter_ext_func_mode(dev);
        pnp_set_logical_device(dev);
        pnp_set_enable(dev, 0);
        pnp_set_iobase(dev, PNP_IDX_IO0, iobase);
        pnp_set_enable(dev, 1);
        pnp_exit_ext_func_mode(dev);
 }

where we defined the functions prototype in the src/superio/vendor/device/device.h as to link it into both the rom and ram stages. We also must statically declarate two helper functions:

 /*
  * Enable configuration: pass entry key '0x87' into index port dev.
  */
 static void pnp_enter_conf_state(device_t dev)
 {
 »       u16 port = dev >> 8;
 »       outb(0x87, port);
 »       outb(0x87, port);
 }
 
 /*
  * Disable configuration: pass exit key '0xAA' into index port dev.
  */
 static void pnp_exit_conf_state(device_t dev)
 {
 »       u16 port = dev >> 8;
 »       outb(0xaa, port);
 }

These two procedures are what put the Super I/O chip into configuration mode and then return it back again.. N.B. The values of 0x87 and 0xAA for enable and disable configuration respectively are typical although check the Super I/O data sheet to be sure. N.B. The default index port and data port are either 0x4E and 0x4F or 0x2E and 0x2F respecively, once again check the data sheet.

Whether the Super I/O is at config address 0x2e (the usual case) or 0x4e (or some other address) is mainboard-dependent. You can find out the address by running superiotool.

This value is usually defined in the mainboards devicetree.cb file under the pnp device in any case.

Mainboards which have this Super I/O chip, will call this function in their romstage.c file. Example:

 #include "superio/winbond/w83627ehg/w83627ehg.h"
 [...]
 #define SERIAL_DEV PNP_DEV(0x2e, W83627EHG_SP1)
 [...]
 w83627ehg_enable_dev(SERIAL_DEV, TTYS0_BASE);
 console_init();

superio.c

While writing the superio.c part of the Super I/O bring up you will encounter the data structure static struct pnp_info pnp_dev_info[] = {} to prepare. The following information may help to understand the LDN mask pairing:

/*
 * io_info contains the mask 0x07f8. Given 8 register, each 8 bits wide of a
 * logical device we need a mask of the following form:
 *
 *  MSB                 LSB
 *    v                 v
 * 0x[15..11][10..3][2..0]
 *    ------  ^^^^^  ^^^^
 *     null     |      |
 *              |      +------ Register index
 *              |
 *              +------------- Compare against base address and
 *                             asserts a chip_select on match.
 *
 * i.e., 0x07F8 = [00000][11111111][000]
 *
 */

A typical superio.c would look like this:

#include <arch/io.h>
#include <device/device.h>
#include <device/pnp.h>
#include <superio/conf_mode.h>
#include <console/console.h>
#include <stdlib.h>

#include "f71869ad.h"

static void f71869ad_init(device_t dev)
{
»       struct superio_fintek_f71869ad_config *conf = dev->chip_info;

»       if (!dev->enabled)
»       »       return;

»       switch(dev->path.pnp.device) {
»       /* TODO: Might potentially need code for HWM or FDC etc. */
»       case F71869AD_KBC:
»       »       pc_keyboard_init(&conf->keyboard);
»       »       break;
»       }
}

static struct device_operations ops = {
»       .read_resources = pnp_read_resources,
»       .set_resources = pnp_set_resources,
»       .enable_resources = pnp_enable_resources,
»       .enable = pnp_alt_enable,
»       .init = f71869ad_init,
»       .ops_pnp_mode = &pnp_conf_mode_8787_aa,
};

static struct pnp_info pnp_dev_info[] = {
»       { &ops, F71869AD_FDC, PNP_IO0 | PNP_IRQ0 | PNP_DRQ0, {0x07f8, 0}, },
»       { &ops, F71869AD_SP1, PNP_IO0 | PNP_IRQ0, {0x07f8, 0}, },
»       { &ops, F71869AD_SP2, PNP_IO0 | PNP_IRQ0, {0x07f8, 0}, },
»       { &ops, F71869AD_PP, PNP_IO0 | PNP_IRQ0 | PNP_DRQ0, {0x07f8, 0}, },
»       { &ops, F71869AD_HWM, PNP_IO0 | PNP_IRQ0, {0x0ff8, 0}, },
»       { &ops, F71869AD_KBC, PNP_IO0 | PNP_IRQ0 | PNP_IRQ1, {0x07ff, 0}, },
»       { &ops, F71869AD_GPIO, },
»       { &ops, F71869AD_BSEL, PNP_IO0, {0x07f8, 0}, },
»       { &ops, F71869AD_PME, },
};

static void enable_dev(device_t dev)
{
»       pnp_enable_devices(dev, &ops, ARRAY_SIZE(pnp_dev_info), pnp_dev_info);
}

struct chip_operations superio_fintek_f71869ad_ops = {
»       CHIP_NAME("Fintek F71869AD Super I/O")
»       .enable_dev = enable_dev
};

Additional resources

If you still have some problems these could come in handy: