// SPDX-License-Identifier: GPL-2.0+
/*
 * ipmi_kcs_sm.c
 *
 * State machine for handling IPMI KCS interfaces.
 *
 * Author: MontaVista Software, Inc.
 *         Corey Minyard <minyard@mvista.com>
 *         source@mvista.com
 *
 * Copyright 2002 MontaVista Software Inc.
 */

/*
 * This state machine is taken from the state machine in the IPMI spec,
 * pretty much verbatim.  If you have questions about the states, see
 * that document.
 */

#define DEBUG /* So dev_dbg() is always available. */

#include <linux/kernel.h> /* For printk. */
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/string.h>
#include <linux/jiffies.h>
#include <linux/ipmi_msgdefs.h>		/* for completion codes */
#include "ipmi_si_sm.h"

/* kcs_debug is a bit-field
 *	KCS_DEBUG_ENABLE -	turned on for now
 *	KCS_DEBUG_MSG    -	commands and their responses
 *	KCS_DEBUG_STATES -	state machine
 */
#define KCS_DEBUG_STATES	4
#define KCS_DEBUG_MSG		2
#define	KCS_DEBUG_ENABLE	1

static int kcs_debug;
module_param(kcs_debug, int, 0644);
MODULE_PARM_DESC(kcs_debug, "debug bitmask, 1=enable, 2=messages, 4=states");

/* The states the KCS driver may be in. */
enum kcs_states {
	/* The KCS interface is currently doing nothing. */
	KCS_IDLE,

	/*
	 * We are starting an operation.  The data is in the output
	 * buffer, but nothing has been done to the interface yet.  This
	 * was added to the state machine in the spec to wait for the
	 * initial IBF.
	 */
	KCS_START_OP,

	/* We have written a write cmd to the interface. */
	KCS_WAIT_WRITE_START,

	/* We are writing bytes to the interface. */
	KCS_WAIT_WRITE,

	/*
	 * We have written the write end cmd to the interface, and
	 * still need to write the last byte.
	 */
	KCS_WAIT_WRITE_END,

	/* We are waiting to read data from the interface. */
	KCS_WAIT_READ,

	/*
	 * State to transition to the error handler, this was added to
	 * the state machine in the spec to be sure IBF was there.
	 */
	KCS_ERROR0,

	/*
	 * First stage error handler, wait for the interface to
	 * respond.
	 */
	KCS_ERROR1,

	/*
	 * The abort cmd has been written, wait for the interface to
	 * respond.
	 */
	KCS_ERROR2,

	/*
	 * We wrote some data to the interface, wait for it to switch
	 * to read mode.
	 */
	KCS_ERROR3,

	/* The hardware failed to follow the state machine. */
	KCS_HOSED
};

#define MAX_KCS_READ_SIZE IPMI_MAX_MSG_LENGTH
#define MAX_KCS_WRITE_SIZE IPMI_MAX_MSG_LENGTH

/* Timeouts in microseconds. */
#define IBF_RETRY_TIMEOUT (5*USEC_PER_SEC)
#define OBF_RETRY_TIMEOUT (5*USEC_PER_SEC)
#define MAX_ERROR_RETRIES 10
#define ERROR0_OBF_WAIT_JIFFIES (2*HZ)

struct si_sm_data {
	enum kcs_states  state;
	struct si_sm_io *io;
	unsigned char    write_data[MAX_KCS_WRITE_SIZE];
	int              write_pos;
	int              write_count;
	int              orig_write_count;
	unsigned char    read_data[MAX_KCS_READ_SIZE];
	int              read_pos;
	int	         truncated;

	unsigned int  error_retries;
	long          ibf_timeout;
	long          obf_timeout;
	unsigned long  error0_timeout;
};

static unsigned int init_kcs_data_with_state(struct si_sm_data *kcs,
				  struct si_sm_io *io, enum kcs_states state)
{
	kcs->state = state;
	kcs->io = io;
	kcs->write_pos = 0;
	kcs->write_count = 0;
	kcs->orig_write_count = 0;
	kcs->read_pos = 0;
	kcs->error_retries = 0;
	kcs->truncated = 0;
	kcs->ibf_timeout = IBF_RETRY_TIMEOUT;
	kcs->obf_timeout = OBF_RETRY_TIMEOUT;

	/* Reserve 2 I/O bytes. */
	return 2;
}

static unsigned int init_kcs_data(struct si_sm_data *kcs,
				  struct si_sm_io *io)
{
	return init_kcs_data_with_state(kcs, io, KCS_IDLE);
}

static inline unsigned char read_status(struct si_sm_data *kcs)
{
	return kcs->io->inputb(kcs->io, 1);
}

static inline unsigned char read_data(struct si_sm_data *kcs)
{
	return kcs->io->inputb(kcs->io, 0);
}

static inline void write_cmd(struct si_sm_data *kcs, unsigned char data)
{
	kcs->io->outputb(kcs->io, 1, data);
}

static inline void write_data(struct si_sm_data *kcs, unsigned char data)
{
	kcs->io->outputb(kcs->io, 0, data);
}

/* Control codes. */
#define KCS_GET_STATUS_ABORT	0x60
#define KCS_WRITE_START		0x61
#define KCS_WRITE_END		0x62
#define KCS_READ_BYTE		0x68

/* Status bits. */
#define GET_STATUS_STATE(status) (((status) >> 6) & 0x03)
#define KCS_IDLE_STATE	0
#define KCS_READ_STATE	1
#define KCS_WRITE_STATE	2
#define KCS_ERROR_STATE	3
#define GET_STATUS_ATN(status) ((status) & 0x04)
#define GET_STATUS_IBF(status) ((status) & 0x02)
#define GET_STATUS_OBF(status) ((status) & 0x01)


static inline void write_next_byte(struct si_sm_data *kcs)
{
	write_data(kcs, kcs->write_data[kcs->write_pos]);
	(kcs->write_pos)++;
	(kcs->write_count)--;
}

static inline void start_error_recovery(struct si_sm_data *kcs, char *reason)
{
	(kcs->error_retries)++;
	if (kcs->error_retries > MAX_ERROR_RETRIES) {
		if (kcs_debug & KCS_DEBUG_ENABLE)
			dev_dbg(kcs->io->dev, "ipmi_kcs_sm: kcs hosed: %s\n",
				reason);
		kcs->state = KCS_HOSED;
	} else {
		kcs->error0_timeout = jiffies + ERROR0_OBF_WAIT_JIFFIES;
		kcs->state = KCS_ERROR0;
	}
}

static inline void read_next_byte(struct si_sm_data *kcs)
{
	if (kcs->read_pos >= MAX_KCS_READ_SIZE) {
		/* Throw the data away and mark it truncated. */
		read_data(kcs);
		kcs->truncated = 1;
	} else {
		kcs->read_data[kcs->read_pos] = read_data(kcs);
		(kcs->read_pos)++;
	}
	write_data(kcs, KCS_READ_BYTE);
}

static inline int check_ibf(struct si_sm_data *kcs, unsigned char status,
			    long time)
{
	if (GET_STATUS_IBF(status)) {
		kcs->ibf_timeout -= time;
		if (kcs->ibf_timeout < 0) {
			start_error_recovery(kcs, "IBF not ready in time");
			kcs->ibf_timeout = IBF_RETRY_TIMEOUT;
			return 1;
		}
		return 0;
	}
	kcs->ibf_timeout = IBF_RETRY_TIMEOUT;
	return 1;
}

static inline int check_obf(struct si_sm_data *kcs, unsigned char status,
			    long time)
{
	if (!GET_STATUS_OBF(status)) {
		kcs->obf_timeout -= time;
		if (kcs->obf_timeout < 0) {
			kcs->obf_timeout = OBF_RETRY_TIMEOUT;
			start_error_recovery(kcs, "OBF not ready in time");
			return 1;
		}
		return 0;
	}
	kcs->obf_timeout = OBF_RETRY_TIMEOUT;
	return 1;
}

static void clear_obf(struct si_sm_data *kcs, unsigned char status)
{
	if (GET_STATUS_OBF(status))
		read_data(kcs);
}

static void restart_kcs_transaction(struct si_sm_data *kcs)
{
	kcs->write_count = kcs->orig_write_count;
	kcs->write_pos = 0;
	kcs->read_pos = 0;
	kcs->state = KCS_WAIT_WRITE_START;
	kcs->ibf_timeout = IBF_RETRY_TIMEOUT;
	kcs->obf_timeout = OBF_RETRY_TIMEOUT;
	write_cmd(kcs, KCS_WRITE_START);
}

static int start_kcs_transaction(struct si_sm_data *kcs, unsigned char *data,
				 unsigned int size)
{
	unsigned int i;

	if (size < 2)
		return IPMI_REQ_LEN_INVALID_ERR;
	if (size > MAX_KCS_WRITE_SIZE)
		return IPMI_REQ_LEN_EXCEEDED_ERR;

	if (kcs->state != KCS_IDLE) {
		dev_warn(kcs->io->dev, "KCS in invalid state %d\n", kcs->state);
		return IPMI_NOT_IN_MY_STATE_ERR;
	}

	if (kcs_debug & KCS_DEBUG_MSG) {
		dev_dbg(kcs->io->dev, "%s -", __func__);
		for (i = 0; i < size; i++)
			pr_cont(" %02x", data[i]);
		pr_cont("\n");
	}
	kcs->error_retries = 0;
	memcpy(kcs->write_data, data, size);
	kcs->write_count = size;
	kcs->orig_write_count = size;
	kcs->write_pos = 0;
	kcs->read_pos = 0;
	kcs->state = KCS_START_OP;
	kcs->ibf_timeout = IBF_RETRY_TIMEOUT;
	kcs->obf_timeout = OBF_RETRY_TIMEOUT;
	return 0;
}

static int get_kcs_result(struct si_sm_data *kcs, unsigned char *data,
			  unsigned int length)
{
	if (length < kcs->read_pos) {
		kcs->read_pos = length;
		kcs->truncated = 1;
	}

	memcpy(data, kcs->read_data, kcs->read_pos);

	if ((length >= 3) && (kcs->read_pos < 3)) {
		/* Guarantee that we return at least 3 bytes, with an
		   error in the third byte if it is too short. */
		data[2] = IPMI_ERR_UNSPECIFIED;
		kcs->read_pos = 3;
	}
	if (kcs->truncated) {
		/*
		 * Report a truncated error.  We might overwrite
		 * another error, but that's too bad, the user needs
		 * to know it was truncated.
		 */
		data[2] = IPMI_ERR_MSG_TRUNCATED;
		kcs->truncated = 0;
	}

	return kcs->read_pos;
}

/*
 * This implements the state machine defined in the IPMI manual, see
 * that for details on how this works.  Divide that flowchart into
 * sections delimited by "Wait for IBF" and this will become clear.
 */
static enum si_sm_result kcs_event(struct si_sm_data *kcs, long time)
{
	unsigned char status;
	unsigned char state;

	status = read_status(kcs);

	if (kcs_debug & KCS_DEBUG_STATES)
		dev_dbg(kcs->io->dev,
			"KCS: State = %d, %x\n", kcs->state, status);

	/* All states wait for ibf, so just do it here. */
	if (!check_ibf(kcs, status, time))
		return SI_SM_CALL_WITH_DELAY;

	/* Just about everything looks at the KCS state, so grab that, too. */
	state = GET_STATUS_STATE(status);

	switch (kcs->state) {
	case KCS_IDLE:
		/* If there's and interrupt source, turn it off. */
		clear_obf(kcs, status);

		if (GET_STATUS_ATN(status))
			return SI_SM_ATTN;
		else
			return SI_SM_IDLE;

	case KCS_START_OP:
		if (state != KCS_IDLE_STATE) {
			start_error_recovery(kcs,
					     "State machine not idle at start");
			break;
		}

		clear_obf(kcs, status);
		write_cmd(kcs, KCS_WRITE_START);
		kcs->state = KCS_WAIT_WRITE_START;
		break;

	case KCS_WAIT_WRITE_START:
		if (state != KCS_WRITE_STATE) {
			start_error_recovery(
				kcs,
				"Not in write state at write start");
			break;
		}
		read_data(kcs);
		if (kcs->write_count == 1) {
			write_cmd(kcs, KCS_WRITE_END);
			kcs->state = KCS_WAIT_WRITE_END;
		} else {
			write_next_byte(kcs);
			kcs->state = KCS_WAIT_WRITE;
		}
		break;

	case KCS_WAIT_WRITE:
		if (state != KCS_WRITE_STATE) {
			start_error_recovery(kcs,
					     "Not in write state for write");
			break;
		}
		clear_obf(kcs, status);
		if (kcs->write_count == 1) {
			write_cmd(kcs, KCS_WRITE_END);
			kcs->state = KCS_WAIT_WRITE_END;
		} else {
			write_next_byte(kcs);
		}
		break;

	case KCS_WAIT_WRITE_END:
		if (state != KCS_WRITE_STATE) {
			start_error_recovery(kcs,
					     "Not in write state"
					     " for write end");
			break;
		}
		clear_obf(kcs, status);
		write_next_byte(kcs);
		kcs->state = KCS_WAIT_READ;
		break;

	case KCS_WAIT_READ:
		if ((state != KCS_READ_STATE) && (state != KCS_IDLE_STATE)) {
			start_error_recovery(
				kcs,
				"Not in read or idle in read state");
			break;
		}

		if (state == KCS_READ_STATE) {
			if (!check_obf(kcs, status, time))
				return SI_SM_CALL_WITH_DELAY;
			read_next_byte(kcs);
		} else {
			/*
			 * We don't implement this exactly like the state
			 * machine in the spec.  Some broken hardware
			 * does not write the final dummy byte to the
			 * read register.  Thus obf will never go high
			 * here.  We just go straight to idle, and we
			 * handle clearing out obf in idle state if it
			 * happens to come in.
			 */
			clear_obf(kcs, status);
			kcs->orig_write_count = 0;
			kcs->state = KCS_IDLE;
			return SI_SM_TRANSACTION_COMPLETE;
		}
		break;

	case KCS_ERROR0:
		clear_obf(kcs, status);
		status = read_status(kcs);
		if (GET_STATUS_OBF(status))
			/* controller isn't responding */
			if (time_before(jiffies, kcs->error0_timeout))
				return SI_SM_CALL_WITH_TICK_DELAY;
		write_cmd(kcs, KCS_GET_STATUS_ABORT);
		kcs->state = KCS_ERROR1;
		break;

	case KCS_ERROR1:
		clear_obf(kcs, status);
		write_data(kcs, 0);
		kcs->state = KCS_ERROR2;
		break;

	case KCS_ERROR2:
		if (state != KCS_READ_STATE) {
			start_error_recovery(kcs,
					     "Not in read state for error2");
			break;
		}
		if (!check_obf(kcs, status, time))
			return SI_SM_CALL_WITH_DELAY;

		clear_obf(kcs, status);
		write_data(kcs, KCS_READ_BYTE);
		kcs->state = KCS_ERROR3;
		break;

	case KCS_ERROR3:
		if (state != KCS_IDLE_STATE) {
			start_error_recovery(kcs,
					     "Not in idle state for error3");
			break;
		}

		if (!check_obf(kcs, status, time))
			return SI_SM_CALL_WITH_DELAY;

		clear_obf(kcs, status);
		if (kcs->orig_write_count) {
			restart_kcs_transaction(kcs);
		} else {
			kcs->state = KCS_IDLE;
			return SI_SM_TRANSACTION_COMPLETE;
		}
		break;

	case KCS_HOSED:
		break;
	}

	if (kcs->state == KCS_HOSED) {
		init_kcs_data_with_state(kcs, kcs->io, KCS_ERROR0);
		return SI_SM_HOSED;
	}

	return SI_SM_CALL_WITHOUT_DELAY;
}

static int kcs_size(void)
{
	return sizeof(struct si_sm_data);
}

static int kcs_detect(struct si_sm_data *kcs)
{
	/*
	 * It's impossible for the KCS status register to be all 1's,
	 * (assuming a properly functioning, self-initialized BMC)
	 * but that's what you get from reading a bogus address, so we
	 * test that first.
	 */
	if (read_status(kcs) == 0xff)
		return 1;

	return 0;
}

static void kcs_cleanup(struct si_sm_data *kcs)
{
}

const struct si_sm_handlers kcs_smi_handlers = {
	.init_data         = init_kcs_data,
	.start_transaction = start_kcs_transaction,
	.get_result        = get_kcs_result,
	.event             = kcs_event,
	.detect            = kcs_detect,
	.cleanup           = kcs_cleanup,
	.size              = kcs_size,
}