// SPDX-License-Identifier: GPL-2.0
/*
 * Device driver for the via ADB on (many) Mac II-class machines
 *
 * Based on the original ADB keyboard handler Copyright (c) 1997 Alan Cox
 * Also derived from code Copyright (C) 1996 Paul Mackerras.
 *
 * With various updates provided over the years by Michael Schmitz,
 * Guideo Koerber and others.
 *
 * Rewrite for Unified ADB by Joshua M. Thompson (funaho@jurai.org)
 *
 * 1999-08-02 (jmt) - Initial rewrite for Unified ADB.
 * 2000-03-29 Tony Mantler <tonym@mac.linux-m68k.org>
 *                              - Big overhaul, should actually work now.
 * 2006-12-31 Finn Thain - Another overhaul.
 *
 * Suggested reading:
 *   Inside Macintosh, ch. 5 ADB Manager
 *   Guide to the Macinstosh Family Hardware, ch. 8 Apple Desktop Bus
 *   Rockwell R6522 VIA datasheet
 *
 * Apple's "ADB Analyzer" bus sniffer is invaluable:
 *   ftp://ftp.apple.com/developer/Tool_Chest/Devices_-_Hardware/Apple_Desktop_Bus/
 */
 
#include <stdarg.h>
#include <linux/types.h>
#include <linux/errno.h>
#include <linux/kernel.h>
#include <linux/delay.h>
#include <linux/adb.h>
#include <linux/interrupt.h>
#include <linux/init.h>
#include <asm/macintosh.h>
#include <asm/macints.h>
#include <asm/mac_via.h>

static volatile unsigned char *via;

/* VIA registers - spaced 0x200 bytes apart */
#define RS              0x200           /* skip between registers */
#define B               0               /* B-side data */
#define A               RS              /* A-side data */
#define DIRB            (2*RS)          /* B-side direction (1=output) */
#define DIRA            (3*RS)          /* A-side direction (1=output) */
#define T1CL            (4*RS)          /* Timer 1 ctr/latch (low 8 bits) */
#define T1CH            (5*RS)          /* Timer 1 counter (high 8 bits) */
#define T1LL            (6*RS)          /* Timer 1 latch (low 8 bits) */
#define T1LH            (7*RS)          /* Timer 1 latch (high 8 bits) */
#define T2CL            (8*RS)          /* Timer 2 ctr/latch (low 8 bits) */
#define T2CH            (9*RS)          /* Timer 2 counter (high 8 bits) */
#define SR              (10*RS)         /* Shift register */
#define ACR             (11*RS)         /* Auxiliary control register */
#define PCR             (12*RS)         /* Peripheral control register */
#define IFR             (13*RS)         /* Interrupt flag register */
#define IER             (14*RS)         /* Interrupt enable register */
#define ANH             (15*RS)         /* A-side data, no handshake */

/* Bits in B data register: all active low */
#define CTLR_IRQ        0x08            /* Controller rcv status (input) */
#define ST_MASK         0x30            /* mask for selecting ADB state bits */

/* Bits in ACR */
#define SR_CTRL         0x1c            /* Shift register control bits */
#define SR_EXT          0x0c            /* Shift on external clock */
#define SR_OUT          0x10            /* Shift out if 1 */

/* Bits in IFR and IER */
#define IER_SET         0x80            /* set bits in IER */
#define IER_CLR         0               /* clear bits in IER */
#define SR_INT          0x04            /* Shift register full/empty */

/* ADB transaction states according to GMHW */
#define ST_CMD          0x00            /* ADB state: command byte */
#define ST_EVEN         0x10            /* ADB state: even data byte */
#define ST_ODD          0x20            /* ADB state: odd data byte */
#define ST_IDLE         0x30            /* ADB state: idle, nothing to send */

static int  macii_init_via(void);
static void macii_start(void);
static irqreturn_t macii_interrupt(int irq, void *arg);
static void macii_queue_poll(void);

static int macii_probe(void);
static int macii_init(void);
static int macii_send_request(struct adb_request *req, int sync);
static int macii_write(struct adb_request *req);
static int macii_autopoll(int devs);
static void macii_poll(void);
static int macii_reset_bus(void);

struct adb_driver via_macii_driver = {
        "Mac II",
        macii_probe,
        macii_init,
        macii_send_request,
        macii_autopoll,
        macii_poll,
        macii_reset_bus
};

static enum macii_state {
        idle,
        sending,
        reading,
        read_done,
} macii_state;

static struct adb_request *current_req; /* first request struct in the queue */
static struct adb_request *last_req;     /* last request struct in the queue */
static unsigned char reply_buf[16];        /* storage for autopolled replies */
static unsigned char *reply_ptr;     /* next byte in reply_buf or req->reply */
static int reading_reply;        /* store reply in reply_buf else req->reply */
static int data_index;      /* index of the next byte to send from req->data */
static int reply_len; /* number of bytes received in reply_buf or req->reply */
static int status;          /* VIA's ADB status bits captured upon interrupt */
static int last_status;              /* status bits as at previous interrupt */
static int srq_asserted;     /* have to poll for the device that asserted it */
static int command_byte;         /* the most recent command byte transmitted */
static int autopoll_devs;      /* bits set are device addresses to be polled */

/* Sanity check for request queue. Doesn't check for cycles. */
static int request_is_queued(struct adb_request *req) {
        struct adb_request *cur;
        unsigned long flags;
        local_irq_save(flags);
        cur = current_req;
        while (cur) {
                if (cur == req) {
                        local_irq_restore(flags);
                        return 1;
                }
                cur = cur->next;
        }
        local_irq_restore(flags);
        return 0;
}

/* Check for MacII style ADB */
static int macii_probe(void)
{
        if (macintosh_config->adb_type != MAC_ADB_II) return -ENODEV;

        via = via1;

        printk("adb: Mac II ADB Driver v1.0 for Unified ADB\n");
        return 0;
}

/* Initialize the driver */
int macii_init(void)
{
        unsigned long flags;
        int err;
        
        local_irq_save(flags);
        
        err = macii_init_via();
        if (err) goto out;

        err = request_irq(IRQ_MAC_ADB, macii_interrupt, 0, "ADB",
                          macii_interrupt);
        if (err) goto out;

        macii_state = idle;
out:
        local_irq_restore(flags);
        return err;
}

/* initialize the hardware */   
static int macii_init_via(void)
{
        unsigned char x;

        /* We want CTLR_IRQ as input and ST_EVEN | ST_ODD as output lines. */
        via[DIRB] = (via[DIRB] | ST_EVEN | ST_ODD) & ~CTLR_IRQ;

        /* Set up state: idle */
        via[B] |= ST_IDLE;
        last_status = via[B] & (ST_MASK|CTLR_IRQ);

        /* Shift register on input */
        via[ACR] = (via[ACR] & ~SR_CTRL) | SR_EXT;

        /* Wipe any pending data and int */
        x = via[SR];

        return 0;
}

/* Send an ADB poll (Talk Register 0 command prepended to the request queue) */
static void macii_queue_poll(void)
{
        /* No point polling the active device as it will never assert SRQ, so
         * poll the next device in the autopoll list. This could leave us
         * stuck in a polling loop if an unprobed device is asserting SRQ.
         * In theory, that could only happen if a device was plugged in after
         * probing started. Unplugging it again will break the cycle.
         * (Simply polling the next higher device often ends up polling almost
         * every device (after wrapping around), which takes too long.)
         */
        int device_mask;
        int next_device;
        static struct adb_request req;

        if (!autopoll_devs) return;

        device_mask = (1 << (((command_byte & 0xF0) >> 4) + 1)) - 1;
        if (autopoll_devs & ~device_mask)
                next_device = ffs(autopoll_devs & ~device_mask) - 1;
        else
                next_device = ffs(autopoll_devs) - 1;

        BUG_ON(request_is_queued(&req));

        adb_request(&req, NULL, ADBREQ_NOSEND, 1,
                    ADB_READREG(next_device, 0));

        req.sent = 0;
        req.complete = 0;
        req.reply_len = 0;
        req.next = current_req;

        if (current_req != NULL) {
                current_req = &req;
        } else {
                current_req = &req;
                last_req = &req;
        }
}

/* Send an ADB request; if sync, poll out the reply 'till it's done */
static int macii_send_request(struct adb_request *req, int sync)
{
        int err;
        unsigned long flags;

        BUG_ON(request_is_queued(req));

        local_irq_save(flags);
        err = macii_write(req);
        local_irq_restore(flags);

        if (!err && sync) {
                while (!req->complete) {
                        macii_poll();
                }
                BUG_ON(request_is_queued(req));
        }

        return err;
}

/* Send an ADB request (append to request queue) */
static int macii_write(struct adb_request *req)
{
        if (req->nbytes < 2 || req->data[0] != ADB_PACKET || req->nbytes > 15) {
                req->complete = 1;
                return -EINVAL;
        }
        
        req->next = NULL;
        req->sent = 0;
        req->complete = 0;
        req->reply_len = 0;

        if (current_req != NULL) {
                last_req->next = req;
                last_req = req;
        } else {
                current_req = req;
                last_req = req;
                if (macii_state == idle) macii_start();
        }
        return 0;
}

/* Start auto-polling */
static int macii_autopoll(int devs)
{
        static struct adb_request req;
        unsigned long flags;
        int err = 0;

        /* bit 1 == device 1, and so on. */
        autopoll_devs = devs & 0xFFFE;

        if (!autopoll_devs) return 0;

        local_irq_save(flags);

        if (current_req == NULL) {
                /* Send a Talk Reg 0. The controller will repeatedly transmit
                 * this as long as it is idle.
                 */
                adb_request(&req, NULL, ADBREQ_NOSEND, 1,
                            ADB_READREG(ffs(autopoll_devs) - 1, 0));
                err = macii_write(&req);
        }

        local_irq_restore(flags);
        return err;
}

static inline int need_autopoll(void) {
        /* Was the last command Talk Reg 0
         * and is the target on the autopoll list?
         */
        if ((command_byte & 0x0F) == 0x0C &&
            ((1 << ((command_byte & 0xF0) >> 4)) & autopoll_devs))
                return 0;
        return 1;
}

/* Prod the chip without interrupts */
static void macii_poll(void)
{
        disable_irq(IRQ_MAC_ADB);
        macii_interrupt(0, NULL);
        enable_irq(IRQ_MAC_ADB);
}

/* Reset the bus */
static int macii_reset_bus(void)
{
        static struct adb_request req;
        
        if (request_is_queued(&req))
                return 0;

        /* Command = 0, Address = ignored */
        adb_request(&req, NULL, 0, 1, ADB_BUSRESET);

        /* Don't want any more requests during the Global Reset low time. */
        udelay(3000);

        return 0;
}

/* Start sending ADB packet */
static void macii_start(void)
{
        struct adb_request *req;

        req = current_req;

        BUG_ON(req == NULL);

        BUG_ON(macii_state != idle);

        /* Now send it. Be careful though, that first byte of the request
         * is actually ADB_PACKET; the real data begins at index 1!
         * And req->nbytes is the number of bytes of real data plus one.
         */

        /* store command byte */
        command_byte = req->data[1];
        /* Output mode */
        via[ACR] |= SR_OUT;
        /* Load data */
        via[SR] = req->data[1];
        /* set ADB state to 'command' */
        via[B] = (via[B] & ~ST_MASK) | ST_CMD;

        macii_state = sending;
        data_index = 2;
}

/*
 * The notorious ADB interrupt handler - does all of the protocol handling.
 * Relies on the ADB controller sending and receiving data, thereby
 * generating shift register interrupts (SR_INT) for us. This means there has
 * to be activity on the ADB bus. The chip will poll to achieve this.
 *
 * The basic ADB state machine was left unchanged from the original MacII code
 * by Alan Cox, which was based on the CUDA driver for PowerMac. 
 * The syntax of the ADB status lines is totally different on MacII,
 * though. MacII uses the states Command -> Even -> Odd -> Even ->...-> Idle
 * for sending and Idle -> Even -> Odd -> Even ->...-> Idle for receiving.
 * Start and end of a receive packet are signalled by asserting /IRQ on the
 * interrupt line (/IRQ means the CTLR_IRQ bit in port B; not to be confused
 * with the VIA shift register interrupt. /IRQ never actually interrupts the
 * processor, it's just an ordinary input.)
 */
static irqreturn_t macii_interrupt(int irq, void *arg)
{
        int x;
        static int entered;
        struct adb_request *req;

        if (!arg) {
                /* Clear the SR IRQ flag when polling. */
                if (via[IFR] & SR_INT)
                        via[IFR] = SR_INT;
                else
                        return IRQ_NONE;
        }

        BUG_ON(entered++);

        last_status = status;
        status = via[B] & (ST_MASK|CTLR_IRQ);

        switch (macii_state) {
                case idle:
                        if (reading_reply) {
                                reply_ptr = current_req->reply;
                        } else {
                                BUG_ON(current_req != NULL);
                                reply_ptr = reply_buf;
                        }

                        x = via[SR];

                        if ((status & CTLR_IRQ) && (x == 0xFF)) {
                                /* Bus timeout without SRQ sequence:
                                 *     data is "FF" while CTLR_IRQ is "H"
                                 */
                                reply_len = 0;
                                srq_asserted = 0;
                                macii_state = read_done;
                        } else {
                                macii_state = reading;
                                *reply_ptr = x;
                                reply_len = 1;
                        }

                        /* set ADB state = even for first data byte */
                        via[B] = (via[B] & ~ST_MASK) | ST_EVEN;
                        break;

                case sending:
                        req = current_req;
                        if (data_index >= req->nbytes) {
                                req->sent = 1;
                                macii_state = idle;

                                if (req->reply_expected) {
                                        reading_reply = 1;
                                } else {
                                        req->complete = 1;
                                        current_req = req->next;
                                        if (req->done) (*req->done)(req);

                                        if (current_req)
                                                macii_start();
                                        else
                                                if (need_autopoll())
                                                        macii_autopoll(autopoll_devs);
                                }

                                if (macii_state == idle) {
                                        /* reset to shift in */
                                        via[ACR] &= ~SR_OUT;
                                        x = via[SR];
                                        /* set ADB state idle - might get SRQ */
                                        via[B] = (via[B] & ~ST_MASK) | ST_IDLE;
                                }
                        } else {
                                via[SR] = req->data[data_index++];

                                if ( (via[B] & ST_MASK) == ST_CMD ) {
                                        /* just sent the command byte, set to EVEN */
                                        via[B] = (via[B] & ~ST_MASK) | ST_EVEN;
                                } else {
                                        /* invert state bits, toggle ODD/EVEN */
                                        via[B] ^= ST_MASK;
                                }
                        }
                        break;

                case reading:
                        x = via[SR];
                        BUG_ON((status & ST_MASK) == ST_CMD ||
                               (status & ST_MASK) == ST_IDLE);

                        /* Bus timeout with SRQ sequence:
                         *     data is "XX FF"      while CTLR_IRQ is "L L"
                         * End of packet without SRQ sequence:
                         *     data is "XX...YY 00" while CTLR_IRQ is "L...H L"
                         * End of packet SRQ sequence:
                         *     data is "XX...YY 00" while CTLR_IRQ is "L...L L"
                         * (where XX is the first response byte and
                         * YY is the last byte of valid response data.)
                         */

                        srq_asserted = 0;
                        if (!(status & CTLR_IRQ)) {
                                if (x == 0xFF) {
                                        if (!(last_status & CTLR_IRQ)) {
                                                macii_state = read_done;
                                                reply_len = 0;
                                                srq_asserted = 1;
                                        }
                                } else if (x == 0x00) {
                                        macii_state = read_done;
                                        if (!(last_status & CTLR_IRQ))
                                                srq_asserted = 1;
                                }
                        }

                        if (macii_state == reading) {
                                BUG_ON(reply_len > 15);
                                reply_ptr++;
                                *reply_ptr = x;
                                reply_len++;
                        }

                        /* invert state bits, toggle ODD/EVEN */
                        via[B] ^= ST_MASK;
                        break;

                case read_done:
                        x = via[SR];

                        if (reading_reply) {
                                reading_reply = 0;
                                req = current_req;
                                req->reply_len = reply_len;
                                req->complete = 1;
                                current_req = req->next;
                                if (req->done) (*req->done)(req);
                        } else if (reply_len && autopoll_devs)
                                adb_input(reply_buf, reply_len, 0);

                        macii_state = idle;

                        /* SRQ seen before, initiate poll now */
                        if (srq_asserted)
                                macii_queue_poll();

                        if (current_req)
                                macii_start();
                        else
                                if (need_autopoll())
                                        macii_autopoll(autopoll_devs);

                        if (macii_state == idle)
                                via[B] = (via[B] & ~ST_MASK) | ST_IDLE;
                        break;

                default:
                break;
        }

        entered--;
        return IRQ_HANDLED;
}