// SPDX-License-Identifier: GPL-2.0+
/*
 *  Serial Port driver for Aspeed VUART device
 *
 *    Copyright (C) 2016 Jeremy Kerr <jk@ozlabs.org>, IBM Corp.
 *    Copyright (C) 2006 Arnd Bergmann <arnd@arndb.de>, IBM Corp.
 */
#include <linux/device.h>
#include <linux/module.h>
#include <linux/of_address.h>
#include <linux/of_irq.h>
#include <linux/of_platform.h>
#include <linux/tty.h>
#include <linux/tty_flip.h>
#include <linux/clk.h>

#include "8250.h"

#define ASPEED_VUART_GCRA               0x20
#define ASPEED_VUART_GCRA_VUART_EN              BIT(0)
#define ASPEED_VUART_GCRA_DISABLE_HOST_TX_DISCARD BIT(5)
#define ASPEED_VUART_GCRB               0x24
#define ASPEED_VUART_GCRB_HOST_SIRQ_MASK        GENMASK(7, 4)
#define ASPEED_VUART_GCRB_HOST_SIRQ_SHIFT       4
#define ASPEED_VUART_ADDRL              0x28
#define ASPEED_VUART_ADDRH              0x2c

struct aspeed_vuart {
        struct device           *dev;
        void __iomem            *regs;
        struct clk              *clk;
        int                     line;
        struct timer_list       unthrottle_timer;
        struct uart_8250_port   *port;
};

/*
 * If we fill the tty flip buffers, we throttle the data ready interrupt
 * to prevent dropped characters. This timeout defines how long we wait
 * to (conditionally, depending on buffer state) unthrottle.
 */
static const int unthrottle_timeout = HZ/10;

/*
 * The VUART is basically two UART 'front ends' connected by their FIFO
 * (no actual serial line in between). One is on the BMC side (management
 * controller) and one is on the host CPU side.
 *
 * It allows the BMC to provide to the host a "UART" that pipes into
 * the BMC itself and can then be turned by the BMC into a network console
 * of some sort for example.
 *
 * This driver is for the BMC side. The sysfs files allow the BMC
 * userspace which owns the system configuration policy, to specify
 * at what IO port and interrupt number the host side will appear
 * to the host on the Host <-> BMC LPC bus. It could be different on a
 * different system (though most of them use 3f8/4).
 */

static ssize_t lpc_address_show(struct device *dev,
                                struct device_attribute *attr, char *buf)
{
        struct aspeed_vuart *vuart = dev_get_drvdata(dev);
        u16 addr;

        addr = (readb(vuart->regs + ASPEED_VUART_ADDRH) << 8) |
                (readb(vuart->regs + ASPEED_VUART_ADDRL));

        return snprintf(buf, PAGE_SIZE - 1, "0x%x\n", addr);
}

static ssize_t lpc_address_store(struct device *dev,
                                 struct device_attribute *attr,
                                 const char *buf, size_t count)
{
        struct aspeed_vuart *vuart = dev_get_drvdata(dev);
        unsigned long val;
        int err;

        err = kstrtoul(buf, 0, &val);
        if (err)
                return err;

        writeb(val >> 8, vuart->regs + ASPEED_VUART_ADDRH);
        writeb(val >> 0, vuart->regs + ASPEED_VUART_ADDRL);

        return count;
}

static DEVICE_ATTR_RW(lpc_address);

static ssize_t sirq_show(struct device *dev,
                         struct device_attribute *attr, char *buf)
{
        struct aspeed_vuart *vuart = dev_get_drvdata(dev);
        u8 reg;

        reg = readb(vuart->regs + ASPEED_VUART_GCRB);
        reg &= ASPEED_VUART_GCRB_HOST_SIRQ_MASK;
        reg >>= ASPEED_VUART_GCRB_HOST_SIRQ_SHIFT;

        return snprintf(buf, PAGE_SIZE - 1, "%u\n", reg);
}

static ssize_t sirq_store(struct device *dev, struct device_attribute *attr,
                          const char *buf, size_t count)
{
        struct aspeed_vuart *vuart = dev_get_drvdata(dev);
        unsigned long val;
        int err;
        u8 reg;

        err = kstrtoul(buf, 0, &val);
        if (err)
                return err;

        val <<= ASPEED_VUART_GCRB_HOST_SIRQ_SHIFT;
        val &= ASPEED_VUART_GCRB_HOST_SIRQ_MASK;

        reg = readb(vuart->regs + ASPEED_VUART_GCRB);
        reg &= ~ASPEED_VUART_GCRB_HOST_SIRQ_MASK;
        reg |= val;
        writeb(reg, vuart->regs + ASPEED_VUART_GCRB);

        return count;
}

static DEVICE_ATTR_RW(sirq);

static struct attribute *aspeed_vuart_attrs[] = {
        &dev_attr_sirq.attr,
        &dev_attr_lpc_address.attr,
        NULL,
};

static const struct attribute_group aspeed_vuart_attr_group = {
        .attrs = aspeed_vuart_attrs,
};

static void aspeed_vuart_set_enabled(struct aspeed_vuart *vuart, bool enabled)
{
        u8 reg = readb(vuart->regs + ASPEED_VUART_GCRA);

        if (enabled)
                reg |= ASPEED_VUART_GCRA_VUART_EN;
        else
                reg &= ~ASPEED_VUART_GCRA_VUART_EN;

        writeb(reg, vuart->regs + ASPEED_VUART_GCRA);
}

static void aspeed_vuart_set_host_tx_discard(struct aspeed_vuart *vuart,
                                             bool discard)
{
        u8 reg;

        reg = readb(vuart->regs + ASPEED_VUART_GCRA);

        /* If the DISABLE_HOST_TX_DISCARD bit is set, discard is disabled */
        if (!discard)
                reg |= ASPEED_VUART_GCRA_DISABLE_HOST_TX_DISCARD;
        else
                reg &= ~ASPEED_VUART_GCRA_DISABLE_HOST_TX_DISCARD;

        writeb(reg, vuart->regs + ASPEED_VUART_GCRA);
}

static int aspeed_vuart_startup(struct uart_port *uart_port)
{
        struct uart_8250_port *uart_8250_port = up_to_u8250p(uart_port);
        struct aspeed_vuart *vuart = uart_8250_port->port.private_data;
        int rc;

        rc = serial8250_do_startup(uart_port);
        if (rc)
                return rc;

        aspeed_vuart_set_host_tx_discard(vuart, false);

        return 0;
}

static void aspeed_vuart_shutdown(struct uart_port *uart_port)
{
        struct uart_8250_port *uart_8250_port = up_to_u8250p(uart_port);
        struct aspeed_vuart *vuart = uart_8250_port->port.private_data;

        aspeed_vuart_set_host_tx_discard(vuart, true);

        serial8250_do_shutdown(uart_port);
}

static void __aspeed_vuart_set_throttle(struct uart_8250_port *up,
                bool throttle)
{
        unsigned char irqs = UART_IER_RLSI | UART_IER_RDI;

        up->ier &= ~irqs;
        if (!throttle)
                up->ier |= irqs;
        serial_out(up, UART_IER, up->ier);
}
static void aspeed_vuart_set_throttle(struct uart_port *port, bool throttle)
{
        struct uart_8250_port *up = up_to_u8250p(port);
        unsigned long flags;

        spin_lock_irqsave(&port->lock, flags);
        __aspeed_vuart_set_throttle(up, throttle);
        spin_unlock_irqrestore(&port->lock, flags);
}

static void aspeed_vuart_throttle(struct uart_port *port)
{
        aspeed_vuart_set_throttle(port, true);
}

static void aspeed_vuart_unthrottle(struct uart_port *port)
{
        aspeed_vuart_set_throttle(port, false);
}

static void aspeed_vuart_unthrottle_exp(struct timer_list *timer)
{
        struct aspeed_vuart *vuart = from_timer(vuart, timer, unthrottle_timer);
        struct uart_8250_port *up = vuart->port;

        if (!tty_buffer_space_avail(&up->port.state->port)) {
                mod_timer(&vuart->unthrottle_timer,
                          jiffies + unthrottle_timeout);
                return;
        }

        aspeed_vuart_unthrottle(&up->port);
}

/*
 * Custom interrupt handler to manage finer-grained flow control. Although we
 * have throttle/unthrottle callbacks, we've seen that the VUART device can
 * deliver characters faster than the ldisc has a chance to check buffer space
 * against the throttle threshold. This results in dropped characters before
 * the throttle.
 *
 * We do this by checking for flip buffer space before RX. If we have no space,
 * throttle now and schedule an unthrottle for later, once the ldisc has had
 * a chance to drain the buffers.
 */
static int aspeed_vuart_handle_irq(struct uart_port *port)
{
        struct uart_8250_port *up = up_to_u8250p(port);
        unsigned int iir, lsr;
        unsigned long flags;
        int space, count;

        iir = serial_port_in(port, UART_IIR);

        if (iir & UART_IIR_NO_INT)
                return 0;

        spin_lock_irqsave(&port->lock, flags);

        lsr = serial_port_in(port, UART_LSR);

        if (lsr & (UART_LSR_DR | UART_LSR_BI)) {
                space = tty_buffer_space_avail(&port->state->port);

                if (!space) {
                        /* throttle and schedule an unthrottle later */
                        struct aspeed_vuart *vuart = port->private_data;
                        __aspeed_vuart_set_throttle(up, true);

                        if (!timer_pending(&vuart->unthrottle_timer)) {
                                vuart->port = up;
                                mod_timer(&vuart->unthrottle_timer,
                                          jiffies + unthrottle_timeout);
                        }

                } else {
                        count = min(space, 256);

                        do {
                                serial8250_read_char(up, lsr);
                                lsr = serial_in(up, UART_LSR);
                                if (--count == 0)
                                        break;
                        } while (lsr & (UART_LSR_DR | UART_LSR_BI));

                        tty_flip_buffer_push(&port->state->port);
                }
        }

        serial8250_modem_status(up);
        if (lsr & UART_LSR_THRE)
                serial8250_tx_chars(up);

        spin_unlock_irqrestore(&port->lock, flags);

        return 1;
}

static int aspeed_vuart_probe(struct platform_device *pdev)
{
        struct uart_8250_port port;
        struct aspeed_vuart *vuart;
        struct device_node *np;
        struct resource *res;
        u32 clk, prop;
        int rc;

        np = pdev->dev.of_node;

        vuart = devm_kzalloc(&pdev->dev, sizeof(*vuart), GFP_KERNEL);
        if (!vuart)
                return -ENOMEM;

        vuart->dev = &pdev->dev;
        timer_setup(&vuart->unthrottle_timer, aspeed_vuart_unthrottle_exp, 0);

        res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
        vuart->regs = devm_ioremap_resource(&pdev->dev, res);
        if (IS_ERR(vuart->regs))
                return PTR_ERR(vuart->regs);

        memset(&port, 0, sizeof(port));
        port.port.private_data = vuart;
        port.port.membase = vuart->regs;
        port.port.mapbase = res->start;
        port.port.mapsize = resource_size(res);
        port.port.startup = aspeed_vuart_startup;
        port.port.shutdown = aspeed_vuart_shutdown;
        port.port.throttle = aspeed_vuart_throttle;
        port.port.unthrottle = aspeed_vuart_unthrottle;
        port.port.status = UPSTAT_SYNC_FIFO;
        port.port.dev = &pdev->dev;

        rc = sysfs_create_group(&vuart->dev->kobj, &aspeed_vuart_attr_group);
        if (rc < 0)
                return rc;

        if (of_property_read_u32(np, "clock-frequency", &clk)) {
                vuart->clk = devm_clk_get(&pdev->dev, NULL);
                if (IS_ERR(vuart->clk)) {
                        dev_warn(&pdev->dev,
                                "clk or clock-frequency not defined\n");
                        rc = PTR_ERR(vuart->clk);
                        goto err_sysfs_remove;
                }

                rc = clk_prepare_enable(vuart->clk);
                if (rc < 0)
                        goto err_sysfs_remove;

                clk = clk_get_rate(vuart->clk);
        }

        /* If current-speed was set, then try not to change it. */
        if (of_property_read_u32(np, "current-speed", &prop) == 0)
                port.port.custom_divisor = clk / (16 * prop);

        /* Check for shifted address mapping */
        if (of_property_read_u32(np, "reg-offset", &prop) == 0)
                port.port.mapbase += prop;

        /* Check for registers offset within the devices address range */
        if (of_property_read_u32(np, "reg-shift", &prop) == 0)
                port.port.regshift = prop;

        /* Check for fifo size */
        if (of_property_read_u32(np, "fifo-size", &prop) == 0)
                port.port.fifosize = prop;

        /* Check for a fixed line number */
        rc = of_alias_get_id(np, "serial");
        if (rc >= 0)
                port.port.line = rc;

        port.port.irq = irq_of_parse_and_map(np, 0);
        port.port.irqflags = IRQF_SHARED;
        port.port.handle_irq = aspeed_vuart_handle_irq;
        port.port.iotype = UPIO_MEM;
        port.port.type = PORT_16550A;
        port.port.uartclk = clk;
        port.port.flags = UPF_SHARE_IRQ | UPF_BOOT_AUTOCONF
                | UPF_FIXED_PORT | UPF_FIXED_TYPE | UPF_NO_THRE_TEST;

        if (of_property_read_bool(np, "no-loopback-test"))
                port.port.flags |= UPF_SKIP_TEST;

        if (port.port.fifosize)
                port.capabilities = UART_CAP_FIFO;

        if (of_property_read_bool(np, "auto-flow-control"))
                port.capabilities |= UART_CAP_AFE;

        rc = serial8250_register_8250_port(&port);
        if (rc < 0)
                goto err_clk_disable;

        vuart->line = rc;

        aspeed_vuart_set_enabled(vuart, true);
        aspeed_vuart_set_host_tx_discard(vuart, true);
        platform_set_drvdata(pdev, vuart);

        return 0;

err_clk_disable:
        clk_disable_unprepare(vuart->clk);
        irq_dispose_mapping(port.port.irq);
err_sysfs_remove:
        sysfs_remove_group(&vuart->dev->kobj, &aspeed_vuart_attr_group);
        return rc;
}

static int aspeed_vuart_remove(struct platform_device *pdev)
{
        struct aspeed_vuart *vuart = platform_get_drvdata(pdev);

        del_timer_sync(&vuart->unthrottle_timer);
        aspeed_vuart_set_enabled(vuart, false);
        serial8250_unregister_port(vuart->line);
        sysfs_remove_group(&vuart->dev->kobj, &aspeed_vuart_attr_group);
        clk_disable_unprepare(vuart->clk);

        return 0;
}

static const struct of_device_id aspeed_vuart_table[] = {
        { .compatible = "aspeed,ast2400-vuart" },
        { .compatible = "aspeed,ast2500-vuart" },
        { },
};

static struct platform_driver aspeed_vuart_driver = {
        .driver = {
                .name = "aspeed-vuart",
                .of_match_table = aspeed_vuart_table,
        },
        .probe = aspeed_vuart_probe,
        .remove = aspeed_vuart_remove,
};

module_platform_driver(aspeed_vuart_driver);

MODULE_AUTHOR("Jeremy Kerr <jk@ozlabs.org>");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("Driver for Aspeed VUART device");