arm-charlcd.c

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/*
 * Driver for the on-board character LCD found on some ARM reference boards
 * This is basically an Hitachi HD44780 LCD with a custom IP block to drive it
 * http://en.wikipedia.org/wiki/HD44780_Character_LCD
 * Currently it will just display the text "ARM Linux" and the linux version
 *
 * License terms: GNU General Public License (GPL) version 2
 * Author: Linus Walleij <[email protected]>
 */
#include <linux/init.h>
#include <linux/module.h>
#include <linux/interrupt.h>
#include <linux/platform_device.h>
#include <linux/completion.h>
#include <linux/delay.h>
#include <linux/io.h>
#include <linux/slab.h>
#include <linux/workqueue.h>
#include <generated/utsrelease.h>

#define DRIVERNAME "arm-charlcd"
#define CHARLCD_TIMEOUT (msecs_to_jiffies(1000))

/* Offsets to registers */
#define CHAR_COM    0x00U
#define CHAR_DAT    0x04U
#define CHAR_RD     0x08U
#define CHAR_RAW    0x0CU
#define CHAR_MASK   0x10U
#define CHAR_STAT   0x14U

#define CHAR_RAW_CLEAR  0x00000000U
#define CHAR_RAW_VALID  0x00000100U

/* Hitachi HD44780 display commands */
#define HD_CLEAR            0x01U
#define HD_HOME             0x02U
#define HD_ENTRYMODE            0x04U
#define HD_ENTRYMODE_INCREMENT      0x02U
#define HD_ENTRYMODE_SHIFT      0x01U
#define HD_DISPCTRL         0x08U
#define HD_DISPCTRL_ON          0x04U
#define HD_DISPCTRL_CURSOR_ON       0x02U
#define HD_DISPCTRL_CURSOR_BLINK    0x01U
#define HD_CRSR_SHIFT           0x10U
#define HD_CRSR_SHIFT_DISPLAY       0x08U
#define HD_CRSR_SHIFT_DISPLAY_RIGHT 0x04U
#define HD_FUNCSET          0x20U
#define HD_FUNCSET_8BIT         0x10U
#define HD_FUNCSET_2_LINES      0x08U
#define HD_FUNCSET_FONT_5X10        0x04U
#define HD_SET_CGRAM            0x40U
#define HD_SET_DDRAM            0x80U
#define HD_BUSY_FLAG            0x80U

struct charlcd {
    struct device *dev;
    u32 phybase;
    u32 physize;
    void __iomem *virtbase;
    int irq;
    struct completion complete;
    struct delayed_work init_work;
};

static irqreturn_t charlcd_interrupt(int irq, void *data)
{
    struct charlcd *lcd = data;
    u8 status;

    status = readl(lcd->virtbase + CHAR_STAT) & 0x01;
    /* Clear IRQ */
    writel(CHAR_RAW_CLEAR, lcd->virtbase + CHAR_RAW);
    if (status)
        complete(&lcd->complete);
    else
        dev_info(lcd->dev, "Spurious IRQ (%02x)\n", status);
    return IRQ_HANDLED;
}


static void charlcd_wait_complete_irq(struct charlcd *lcd)
{
    int ret;

    ret = wait_for_completion_interruptible_timeout(&lcd->complete,
                            CHARLCD_TIMEOUT);
    /* Disable IRQ after completion */
    writel(0x00, lcd->virtbase + CHAR_MASK);

    if (ret < 0) {
        dev_err(lcd->dev,
            "wait_for_completion_interruptible_timeout() "
            "returned %d waiting for ready\n", ret);
        return;
    }

    if (ret == 0) {
        dev_err(lcd->dev, "charlcd controller timed out "
            "waiting for ready\n");
        return;
    }
}

static u8 charlcd_4bit_read_char(struct charlcd *lcd)
{
    u8 data;
    u32 val;
    int i;

    /* If we can, use an IRQ to wait for the data, else poll */
    if (lcd->irq >= 0)
        charlcd_wait_complete_irq(lcd);
    else {
        i = 0;
        val = 0;
        while (!(val & CHAR_RAW_VALID) && i < 10) {
            udelay(100);
            val = readl(lcd->virtbase + CHAR_RAW);
            i++;
        }

        writel(CHAR_RAW_CLEAR, lcd->virtbase + CHAR_RAW);
    }
    msleep(1);

    /* Read the 4 high bits of the data */
    data = readl(lcd->virtbase + CHAR_RD) & 0xf0;

    /*
     * The second read for the low bits does not trigger an IRQ
     * so in this case we have to poll for the 4 lower bits
     */
    i = 0;
    val = 0;
    while (!(val & CHAR_RAW_VALID) && i < 10) {
        udelay(100);
        val = readl(lcd->virtbase + CHAR_RAW);
        i++;
    }
    writel(CHAR_RAW_CLEAR, lcd->virtbase + CHAR_RAW);
    msleep(1);

    /* Read the 4 low bits of the data */
    data |= (readl(lcd->virtbase + CHAR_RD) >> 4) & 0x0f;

    return data;
}

static bool charlcd_4bit_read_bf(struct charlcd *lcd)
{
    if (lcd->irq >= 0) {
        /*
         * If we'll use IRQs to wait for the busyflag, clear any
         * pending flag and enable IRQ
         */
        writel(CHAR_RAW_CLEAR, lcd->virtbase + CHAR_RAW);
        init_completion(&lcd->complete);
        writel(0x01, lcd->virtbase + CHAR_MASK);
    }
    readl(lcd->virtbase + CHAR_COM);
    return charlcd_4bit_read_char(lcd) & HD_BUSY_FLAG ? true : false;
}

static void charlcd_4bit_wait_busy(struct charlcd *lcd)
{
    int retries = 50;

    udelay(100);
    while (charlcd_4bit_read_bf(lcd) && retries)
        retries--;
    if (!retries)
        dev_err(lcd->dev, "timeout waiting for busyflag\n");
}

static void charlcd_4bit_command(struct charlcd *lcd, u8 cmd)
{
    u32 cmdlo = (cmd << 4) & 0xf0;
    u32 cmdhi = (cmd & 0xf0);

    writel(cmdhi, lcd->virtbase + CHAR_COM);
    udelay(10);
    writel(cmdlo, lcd->virtbase + CHAR_COM);
    charlcd_4bit_wait_busy(lcd);
}

static void charlcd_4bit_char(struct charlcd *lcd, u8 ch)
{
    u32 chlo = (ch << 4) & 0xf0;
    u32 chhi = (ch & 0xf0);

    writel(chhi, lcd->virtbase + CHAR_DAT);
    udelay(10);
    writel(chlo, lcd->virtbase + CHAR_DAT);
    charlcd_4bit_wait_busy(lcd);
}

static void charlcd_4bit_print(struct charlcd *lcd, int line, const char *str)
{
    u8 offset;
    int i;

    /*
     * We support line 0, 1
     * Line 1 runs from 0x00..0x27
     * Line 2 runs from 0x28..0x4f
     */
    if (line == 0)
        offset = 0;
    else if (line == 1)
        offset = 0x28;
    else
        return;

    /* Set offset */
    charlcd_4bit_command(lcd, HD_SET_DDRAM | offset);

    /* Send string */
    for (i = 0; i < strlen(str) && i < 0x28; i++)
        charlcd_4bit_char(lcd, str[i]);
}

static void charlcd_4bit_init(struct charlcd *lcd)
{
    /* These commands cannot be checked with the busy flag */
    writel(HD_FUNCSET | HD_FUNCSET_8BIT, lcd->virtbase + CHAR_COM);
    msleep(5);
    writel(HD_FUNCSET | HD_FUNCSET_8BIT, lcd->virtbase + CHAR_COM);
    udelay(100);
    writel(HD_FUNCSET | HD_FUNCSET_8BIT, lcd->virtbase + CHAR_COM);
    udelay(100);
    /* Go to 4bit mode */
    writel(HD_FUNCSET, lcd->virtbase + CHAR_COM);
    udelay(100);
    /*
     * 4bit mode, 2 lines, 5x8 font, after this the number of lines
     * and the font cannot be changed until the next initialization sequence
     */
    charlcd_4bit_command(lcd, HD_FUNCSET | HD_FUNCSET_2_LINES);
    charlcd_4bit_command(lcd, HD_DISPCTRL | HD_DISPCTRL_ON);
    charlcd_4bit_command(lcd, HD_ENTRYMODE | HD_ENTRYMODE_INCREMENT);
    charlcd_4bit_command(lcd, HD_CLEAR);
    charlcd_4bit_command(lcd, HD_HOME);
    /* Put something useful in the display */
    charlcd_4bit_print(lcd, 0, "ARM Linux");
    charlcd_4bit_print(lcd, 1, UTS_RELEASE);
}

static void charlcd_init_work(struct work_struct *work)
{
    struct charlcd *lcd =
        container_of(work, struct charlcd, init_work.work);

    charlcd_4bit_init(lcd);
}

static int __init charlcd_probe(struct platform_device *pdev)
{
    int ret;
    struct charlcd *lcd;
    struct resource *res;

    lcd = kzalloc(sizeof(struct charlcd), GFP_KERNEL);
    if (!lcd)
        return -ENOMEM;

    lcd->dev = &pdev->dev;

    res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
    if (!res) {
        ret = -ENOENT;
        goto out_no_resource;
    }
    lcd->phybase = res->start;
    lcd->physize = resource_size(res);

    if (request_mem_region(lcd->phybase, lcd->physize,
                   DRIVERNAME) == NULL) {
        ret = -EBUSY;
        goto out_no_memregion;
    }

    lcd->virtbase = ioremap(lcd->phybase, lcd->physize);
    if (!lcd->virtbase) {
        ret = -ENOMEM;
        goto out_no_remap;
    }

    lcd->irq = platform_get_irq(pdev, 0);
    /* If no IRQ is supplied, we'll survive without it */
    if (lcd->irq >= 0) {
        if (request_irq(lcd->irq, charlcd_interrupt, IRQF_DISABLED,
                DRIVERNAME, lcd)) {
            ret = -EIO;
            goto out_no_irq;
        }
    }

    platform_set_drvdata(pdev, lcd);

    /*
     * Initialize the display in a delayed work, because
     * it is VERY slow and would slow down the boot of the system.
     */
    INIT_DELAYED_WORK(&lcd->init_work, charlcd_init_work);
    schedule_delayed_work(&lcd->init_work, 0);

    dev_info(&pdev->dev, "initialized ARM character LCD at %08x\n",
        lcd->phybase);

    return 0;

out_no_irq:
    iounmap(lcd->virtbase);
out_no_remap:
    platform_set_drvdata(pdev, NULL);
out_no_memregion:
    release_mem_region(lcd->phybase, SZ_4K);
out_no_resource:
    kfree(lcd);
    return ret;
}

static int __exit charlcd_remove(struct platform_device *pdev)
{
    struct charlcd *lcd = platform_get_drvdata(pdev);

    if (lcd) {
        free_irq(lcd->irq, lcd);
        iounmap(lcd->virtbase);
        release_mem_region(lcd->phybase, lcd->physize);
        platform_set_drvdata(pdev, NULL);
        kfree(lcd);
    }

    return 0;
}

static int charlcd_suspend(struct device *dev)
{
    struct platform_device *pdev = to_platform_device(dev);
    struct charlcd *lcd = platform_get_drvdata(pdev);

    /* Power the display off */
    charlcd_4bit_command(lcd, HD_DISPCTRL);
    return 0;
}

static int charlcd_resume(struct device *dev)
{
    struct platform_device *pdev = to_platform_device(dev);
    struct charlcd *lcd = platform_get_drvdata(pdev);

    /* Turn the display back on */
    charlcd_4bit_command(lcd, HD_DISPCTRL | HD_DISPCTRL_ON);
    return 0;
}

static const struct dev_pm_ops charlcd_pm_ops = {
    .suspend = charlcd_suspend,
    .resume = charlcd_resume,
};

static struct platform_driver charlcd_driver = {
    .driver = {
        .name = DRIVERNAME,
        .owner = THIS_MODULE,
        .pm = &charlcd_pm_ops,
    },
    .remove = __exit_p(charlcd_remove),
};

static int __init charlcd_init(void)
{
    return platform_driver_probe(&charlcd_driver, charlcd_probe);
}

static void __exit charlcd_exit(void)
{
    platform_driver_unregister(&charlcd_driver);
}

module_init(charlcd_init);
module_exit(charlcd_exit);

MODULE_AUTHOR("Linus Walleij <[email protected]>");
MODULE_DESCRIPTION("ARM Character LCD Driver");
MODULE_LICENSE("GPL v2");