/*
 *      Bus error event handling code for DECstation/DECsystem 3100
 *      and 2100 (KN01) systems equipped with parity error detection
 *      logic.
 *
 *      Copyright (c) 2005  Maciej W. Rozycki
 *
 *      This program is free software; you can redistribute it and/or
 *      modify it under the terms of the GNU General Public License
 *      as published by the Free Software Foundation; either version
 *      2 of the License, or (at your option) any later version.
 */

#include <linux/init.h>
#include <linux/interrupt.h>
#include <linux/kernel.h>
#include <linux/spinlock.h>
#include <linux/types.h>

#include <asm/inst.h>
#include <asm/irq_regs.h>
#include <asm/mipsregs.h>
#include <asm/page.h>
#include <asm/ptrace.h>
#include <asm/traps.h>
#include <asm/uaccess.h>

#include <asm/dec/kn01.h>


/* CP0 hazard avoidance. */
#define BARRIER                         \
        __asm__ __volatile__(           \
                ".set   push\n\t"       \
                ".set   noreorder\n\t"  \
                "nop\n\t"               \
                ".set   pop\n\t")

/*
 * Bits 7:0 of the Control Register are write-only -- the
 * corresponding bits of the Status Register have a different
 * meaning.  Hence we use a cache.  It speeds up things a bit
 * as well.
 *
 * There is no default value -- it has to be initialized.
 */
u16 cached_kn01_csr;
static DEFINE_RAW_SPINLOCK(kn01_lock);


static inline void dec_kn01_be_ack(void)
{
        volatile u16 *csr = (void *)CKSEG1ADDR(KN01_SLOT_BASE + KN01_CSR);
        unsigned long flags;

        raw_spin_lock_irqsave(&kn01_lock, flags);

        *csr = cached_kn01_csr | KN01_CSR_MEMERR;       /* Clear bus IRQ. */
        iob();

        raw_spin_unlock_irqrestore(&kn01_lock, flags);
}

static int dec_kn01_be_backend(struct pt_regs *regs, int is_fixup, int invoker)
{
        volatile u32 *kn01_erraddr = (void *)CKSEG1ADDR(KN01_SLOT_BASE +
                                                        KN01_ERRADDR);

        static const char excstr[] = "exception";
        static const char intstr[] = "interrupt";
        static const char cpustr[] = "CPU";
        static const char mreadstr[] = "memory read";
        static const char readstr[] = "read";
        static const char writestr[] = "write";
        static const char timestr[] = "timeout";
        static const char paritystr[] = "parity error";

        int data = regs->cp0_cause & 4;
        unsigned int __user *pc = (unsigned int __user *)regs->cp0_epc +
                                  ((regs->cp0_cause & CAUSEF_BD) != 0);
        union mips_instruction insn;
        unsigned long entrylo, offset;
        long asid, entryhi, vaddr;

        const char *kind, *agent, *cycle, *event;
        unsigned long address;

        u32 erraddr = *kn01_erraddr;
        int action = MIPS_BE_FATAL;

        /* Ack ASAP, so that any subsequent errors get caught. */
        dec_kn01_be_ack();

        kind = invoker ? intstr : excstr;

        agent = cpustr;

        if (invoker)
                address = erraddr;
        else {
                /* Bloody hardware doesn't record the address for reads... */
                if (data) {
                        /* This never faults. */
                        __get_user(insn.word, pc);
                        vaddr = regs->regs[insn.i_format.rs] +
                                insn.i_format.simmediate;
                } else
                        vaddr = (long)pc;
                if (KSEGX(vaddr) == CKSEG0 || KSEGX(vaddr) == CKSEG1)
                        address = CPHYSADDR(vaddr);
                else {
                        /* Peek at what physical address the CPU used. */
                        asid = read_c0_entryhi();
                        entryhi = asid & (PAGE_SIZE - 1);
                        entryhi |= vaddr & ~(PAGE_SIZE - 1);
                        write_c0_entryhi(entryhi);
                        BARRIER;
                        tlb_probe();
                        /* No need to check for presence. */
                        tlb_read();
                        entrylo = read_c0_entrylo0();
                        write_c0_entryhi(asid);
                        offset = vaddr & (PAGE_SIZE - 1);
                        address = (entrylo & ~(PAGE_SIZE - 1)) | offset;
                }
        }

        /* Treat low 256MB as memory, high -- as I/O. */
        if (address < 0x10000000) {
                cycle = mreadstr;
                event = paritystr;
        } else {
                cycle = invoker ? writestr : readstr;
                event = timestr;
        }

        if (is_fixup)
                action = MIPS_BE_FIXUP;

        if (action != MIPS_BE_FIXUP)
                printk(KERN_ALERT "Bus error %s: %s %s %s at %#010lx\n",
                        kind, agent, cycle, event, address);

        return action;
}

int dec_kn01_be_handler(struct pt_regs *regs, int is_fixup)
{
        return dec_kn01_be_backend(regs, is_fixup, 0);
}

irqreturn_t dec_kn01_be_interrupt(int irq, void *dev_id)
{
        volatile u16 *csr = (void *)CKSEG1ADDR(KN01_SLOT_BASE + KN01_CSR);
        struct pt_regs *regs = get_irq_regs();
        int action;

        if (!(*csr & KN01_CSR_MEMERR))
                return IRQ_NONE;                /* Must have been video. */

        action = dec_kn01_be_backend(regs, 0, 1);

        if (action == MIPS_BE_DISCARD)
                return IRQ_HANDLED;

        /*
         * FIXME: Find the affected processes and kill them, otherwise
         * we must die.
         *
         * The interrupt is asynchronously delivered thus EPC and RA
         * may be irrelevant, but are printed for a reference.
         */
        printk(KERN_ALERT "Fatal bus interrupt, epc == %08lx, ra == %08lx\n",
               regs->cp0_epc, regs->regs[31]);
        die("Unrecoverable bus error", regs);
}


void __init dec_kn01_be_init(void)
{
        volatile u16 *csr = (void *)CKSEG1ADDR(KN01_SLOT_BASE + KN01_CSR);
        unsigned long flags;

        raw_spin_lock_irqsave(&kn01_lock, flags);

        /* Preset write-only bits of the Control Register cache. */
        cached_kn01_csr = *csr;
        cached_kn01_csr &= KN01_CSR_STATUS | KN01_CSR_PARDIS | KN01_CSR_TXDIS;
        cached_kn01_csr |= KN01_CSR_LEDS;

        /* Enable parity error detection. */
        cached_kn01_csr &= ~KN01_CSR_PARDIS;
        *csr = cached_kn01_csr;
        iob();

        raw_spin_unlock_irqrestore(&kn01_lock, flags);

        /* Clear any leftover errors from the firmware. */
        dec_kn01_be_ack();
}