// SPDX-License-Identifier: GPL-2.0
/*
 * Freescale 16550 UART "driver", Copyright (C) 2011 Paul Gortmaker.
 * Copyright 2020 NXP
 * Copyright 2020 Puresoftware Ltd.
 *
 * This isn't a full driver; it just provides an alternate IRQ
 * handler to deal with an errata and provide ACPI wrapper.
 * Everything else is just using the bog standard 8250 support.
 *
 * We follow code flow of serial8250_default_handle_irq() but add
 * a check for a break and insert a dummy read on the Rx for the
 * immediately following IRQ event.
 *
 * We re-use the already existing "bug handling" lsr_saved_flags
 * field to carry the "what we just did" information from the one
 * IRQ event to the next one.
 */

#include <linux/acpi.h>
#include <linux/serial_reg.h>
#include <linux/serial_8250.h>

#include "8250.h"

int fsl8250_handle_irq(struct uart_port *port)
{
        unsigned long flags;
        u16 lsr, orig_lsr;
        unsigned int iir;
        struct uart_8250_port *up = up_to_u8250p(port);

        uart_port_lock_irqsave(&up->port, &flags);

        iir = serial_port_in(port, UART_IIR);
        if (iir & UART_IIR_NO_INT) {
                uart_port_unlock_irqrestore(&up->port, flags);
                return 0;
        }

        /*
         * For a single break the hardware reports LSR.BI for each character
         * time. This is described in the MPC8313E chip errata as "General17".
         * A typical break has a duration of 0.3s, with a 115200n8 configuration
         * that (theoretically) corresponds to ~3500 interrupts in these 0.3s.
         * In practise it's less (around 500) because of hardware
         * and software latencies. The workaround recommended by the vendor is
         * to read the RX register (to clear LSR.DR and thus prevent a FIFO
         * aging interrupt). To prevent the irq from retriggering LSR must not be
         * read. (This would clear LSR.BI, hardware would reassert the BI event
         * immediately and interrupt the CPU again. The hardware clears LSR.BI
         * when the next valid char is read.)
         */
        if (unlikely((iir & UART_IIR_ID) == UART_IIR_RLSI &&
                     (up->lsr_saved_flags & UART_LSR_BI))) {
                up->lsr_saved_flags &= ~UART_LSR_BI;
                serial_port_in(port, UART_RX);
                uart_port_unlock_irqrestore(&up->port, flags);
                return 1;
        }

        lsr = orig_lsr = serial_port_in(port, UART_LSR);

        /* Process incoming characters first */
        if ((lsr & (UART_LSR_DR | UART_LSR_BI)) &&
            (up->ier & (UART_IER_RLSI | UART_IER_RDI))) {
                lsr = serial8250_rx_chars(up, lsr);
        }

        /* Stop processing interrupts on input overrun */
        if ((orig_lsr & UART_LSR_OE) && (up->overrun_backoff_time_ms > 0)) {
                unsigned long delay;

                up->ier = serial_port_in(port, UART_IER);
                if (up->ier & (UART_IER_RLSI | UART_IER_RDI)) {
                        port->ops->stop_rx(port);
                } else {
                        /* Keep restarting the timer until
                         * the input overrun subsides.
                         */
                        cancel_delayed_work(&up->overrun_backoff);
                }

                delay = msecs_to_jiffies(up->overrun_backoff_time_ms);
                schedule_delayed_work(&up->overrun_backoff, delay);
        }

        serial8250_modem_status(up);

        if ((lsr & UART_LSR_THRE) && (up->ier & UART_IER_THRI))
                serial8250_tx_chars(up);

        up->lsr_saved_flags |= orig_lsr & UART_LSR_BI;

        uart_unlock_and_check_sysrq_irqrestore(&up->port, flags);

        return 1;
}
EXPORT_SYMBOL_GPL(fsl8250_handle_irq);

#ifdef CONFIG_ACPI
struct fsl8250_data {
        int     line;
};

static int fsl8250_acpi_probe(struct platform_device *pdev)
{
        struct fsl8250_data *data;
        struct uart_8250_port port8250;
        struct device *dev = &pdev->dev;
        struct resource *regs;

        int ret, irq;

        regs = platform_get_resource(pdev, IORESOURCE_MEM, 0);
        if (!regs) {
                dev_err(dev, "no registers defined\n");
                return -EINVAL;
        }

        irq = platform_get_irq(pdev, 0);
        if (irq < 0)
                return irq;

        memset(&port8250, 0, sizeof(port8250));

        ret = device_property_read_u32(dev, "clock-frequency",
                                        &port8250.port.uartclk);
        if (ret)
                return ret;

        spin_lock_init(&port8250.port.lock);

        port8250.port.mapbase           = regs->start;
        port8250.port.irq               = irq;
        port8250.port.handle_irq        = fsl8250_handle_irq;
        port8250.port.type              = PORT_16550A;
        port8250.port.flags             = UPF_SHARE_IRQ | UPF_BOOT_AUTOCONF
                                                | UPF_FIXED_PORT | UPF_IOREMAP
                                                | UPF_FIXED_TYPE;
        port8250.port.dev               = dev;
        port8250.port.mapsize           = resource_size(regs);
        port8250.port.iotype            = UPIO_MEM;
        port8250.port.irqflags          = IRQF_SHARED;

        port8250.port.membase = devm_ioremap(dev,  port8250.port.mapbase,
                                                        port8250.port.mapsize);
        if (!port8250.port.membase)
                return -ENOMEM;

        data = devm_kzalloc(dev, sizeof(*data), GFP_KERNEL);
        if (!data)
                return -ENOMEM;

        data->line = serial8250_register_8250_port(&port8250);
        if (data->line < 0)
                return data->line;

        platform_set_drvdata(pdev, data);
        return 0;
}

static void fsl8250_acpi_remove(struct platform_device *pdev)
{
        struct fsl8250_data *data = platform_get_drvdata(pdev);

        serial8250_unregister_port(data->line);
}

static const struct acpi_device_id fsl_8250_acpi_id[] = {
        { "NXP0018", 0 },
        { },
};
MODULE_DEVICE_TABLE(acpi, fsl_8250_acpi_id);

static struct platform_driver fsl8250_platform_driver = {
        .driver = {
                .name                   = "fsl-16550-uart",
                .acpi_match_table       = ACPI_PTR(fsl_8250_acpi_id),
        },
        .probe                  = fsl8250_acpi_probe,
        .remove                 = fsl8250_acpi_remove,
};

module_platform_driver(fsl8250_platform_driver);
#endif

MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("Handling of Freescale specific 8250 variants");