text: // SPDX-License-Identifier: GPL-2.0
  /*
   * Renesas RIIC driver
   *
   * Copyright (C) 2013 Wolfram Sang <wsa@sang-engineering.com>
   * Copyright (C) 2013 Renesas Solutions Corp.
   */
  
  /*
   * This i2c core has a lot of interrupts, namely 8. We use their chaining as
   * some kind of state machine.
   *
   * 1) The main xfer routine kicks off a transmission by putting the start bit
   * (or repeated start) on the bus and enabling the transmit interrupt (TIE)
   * since we need to send the slave address + RW bit in every case.
   *
   * 2) TIE sends slave address + RW bit and selects how to continue.
   *
   * 3a) Write case: We keep utilizing TIE as long as we have data to send. If we
   * are done, we switch over to the transmission done interrupt (TEIE) and mark
   * the message as completed (includes sending STOP) there.
   *
   * 3b) Read case: We switch over to receive interrupt (RIE). One dummy read is
   * needed to start clocking, then we keep receiving until we are done. Note
   * that we use the RDRFS mode all the time, i.e. we ACK/NACK every byte by
   * writing to the ACKBT bit. I tried using the RDRFS mode only at the end of a
   * message to create the final NACK as sketched in the datasheet. This caused
   * some subtle races (when byte n was processed and byte n+1 was already
   * waiting), though, and I started with the safe approach.
   *
   * 4) If we got a NACK somewhere, we flag the error and stop the transmission
   * via NAKIE.
   *
   * Also check the comments in the interrupt routines for some gory details.
   */
  
  #include <linux/clk.h>
  #include <linux/completion.h>
  #include <linux/err.h>
  #include <linux/i2c.h>
  #include <linux/interrupt.h>
  #include <linux/io.h>
  #include <linux/module.h>
  #include <linux/of.h>
  #include <linux/platform_device.h>
  
  #define RIIC_ICCR1	0x00
  #define RIIC_ICCR2	0x04
  #define RIIC_ICMR1	0x08
  #define RIIC_ICMR3	0x10
  #define RIIC_ICSER	0x18
  #define RIIC_ICIER	0x1c
  #define RIIC_ICSR2	0x24
  #define RIIC_ICBRL	0x34
  #define RIIC_ICBRH	0x38
  #define RIIC_ICDRT	0x3c
  #define RIIC_ICDRR	0x40
  
  #define ICCR1_ICE	0x80
  #define ICCR1_IICRST	0x40
  #define ICCR1_SOWP	0x10
  
  #define ICCR2_BBSY	0x80
  #define ICCR2_SP	0x08
  #define ICCR2_RS	0x04
  #define ICCR2_ST	0x02
  
  #define ICMR1_CKS_MASK	0x70
  #define ICMR1_BCWP	0x08
  #define ICMR1_CKS(_x)	((((_x) << 4) & ICMR1_CKS_MASK) | ICMR1_BCWP)
  
  #define ICMR3_RDRFS	0x20
  #define ICMR3_ACKWP	0x10
  #define ICMR3_ACKBT	0x08
  
  #define ICIER_TIE	0x80
  #define ICIER_TEIE	0x40
  #define ICIER_RIE	0x20
  #define ICIER_NAKIE	0x10
  #define ICIER_SPIE	0x08
  
  #define ICSR2_NACKF	0x10
  
  #define ICBR_RESERVED	0xe0 /* Should be 1 on writes */
  
  #define RIIC_INIT_MSG	-1
  
  struct riic_dev {
  	void __iomem *base;
  	u8 *buf;
  	struct i2c_msg *msg;
  	int bytes_left;
  	int err;
  	int is_last;
  	struct completion msg_done;
  	struct i2c_adapter adapter;
  	struct clk *clk;
  };
  
  struct riic_irq_desc {
  	int res_num;
  	irq_handler_t isr;
  	char *name;
  };
  
  static inline void riic_clear_set_bit(struct riic_dev *riic, u8 clear, u8 set, u8 reg)
  {
  	writeb((readb(riic->base + reg) & ~clear) | set, riic->base + reg);
  }
  
  static int riic_xfer(struct i2c_adapter *adap, struct i2c_msg msgs[], int num)
  {
  	struct riic_dev *riic = i2c_get_adapdata(adap);
  	unsigned long time_left;
  	int i, ret;
  	u8 start_bit;
  
  	ret = clk_prepare_enable(riic->clk);
  	if (ret)
  		return ret;
  
  	if (readb(riic->base + RIIC_ICCR2) & ICCR2_BBSY) {
  		riic->err = -EBUSY;
  		goto out;
  	}
  
  	reinit_completion(&riic->msg_done);
  	riic->err = 0;
  
  	writeb(0, riic->base + RIIC_ICSR2);
  
  	for (i = 0, start_bit = ICCR2_ST; i < num; i++) {
  		riic->bytes_left = RIIC_INIT_MSG;
  		riic->buf = msgs[i].buf;
  		riic->msg = &msgs[i];
  		riic->is_last = (i == num - 1);
  
  		writeb(ICIER_NAKIE | ICIER_TIE, riic->base + RIIC_ICIER);
  
  		writeb(start_bit, riic->base + RIIC_ICCR2);
  
  		time_left = wait_for_completion_timeout(&riic->msg_done, riic->adapter.timeout);
  		if (time_left == 0)
  			riic->err = -ETIMEDOUT;
  
  		if (riic->err)
  			break;
  
  		start_bit = ICCR2_RS;
  	}
  
   out:
  	clk_disable_unprepare(riic->clk);
  
  	return riic->err ?: num;
  }
  
  static irqreturn_t riic_tdre_isr(int irq, void *data)
  {
  	struct riic_dev *riic = data;
  	u8 val;
  
  	if (!riic->bytes_left)
  		return IRQ_NONE;
  
  	if (riic->bytes_left == RIIC_INIT_MSG) {
  		if (riic->msg->flags & I2C_M_RD)
  			/* On read, switch over to receive interrupt */
  			riic_clear_set_bit(riic, ICIER_TIE, ICIER_RIE, RIIC_ICIER);
  		else
  			/* On write, initialize length */
  			riic->bytes_left = riic->msg->len;
  
  		val = i2c_8bit_addr_from_msg(riic->msg);
  	} else {
  		val = *riic->buf;
  		riic->buf++;
  		riic->bytes_left--;
  	}
  
  	/*
  	 * Switch to transmission ended interrupt when done. Do check here
  	 * after bytes_left was initialized to support SMBUS_QUICK (new msg has
  	 * 0 length then)
  	 */
  	if (riic->bytes_left == 0)
  		riic_clear_set_bit(riic, ICIER_TIE, ICIER_TEIE, RIIC_ICIER);
  
  	/*
  	 * This acks the TIE interrupt. We get another TIE immediately if our
  	 * value could be moved to the shadow shift register right away. So
  	 * this must be after updates to ICIER (where we want to disable TIE)!
  	 */
  	writeb(val, riic->base + RIIC_ICDRT);
  
  	return IRQ_HANDLED;
  }
  
  static irqreturn_t riic_tend_isr(int irq, void *data)
  {
  	struct riic_dev *riic = data;
  
  	if (readb(riic->base + RIIC_ICSR2) & ICSR2_NACKF) {
  		/* We got a NACKIE */
  		readb(riic->base + RIIC_ICDRR);	/* dummy read */
  		riic->err = -ENXIO;
  	} else if (riic->bytes_left) {
  		return IRQ_NONE;
  	}
  
  	if (riic->is_last || riic->err) {
  		riic_clear_set_bit(riic, ICIER_TEIE, ICIER_SPIE, RIIC_ICIER);
  		writeb(ICCR2_SP, riic->base + RIIC_ICCR2);
  	} else {
  		/* Transfer is complete, but do not send STOP */
  		riic_clear_set_bit(riic, ICIER_TEIE, 0, RIIC_ICIER);
  		complete(&riic->msg_done);
  	}
  
  	return IRQ_HANDLED;
  }
  
  static irqreturn_t riic_rdrf_isr(int irq, void *data)
  {
  	struct riic_dev *riic = data;
  
  	if (!riic->bytes_left)
  		return IRQ_NONE;
  
  	if (riic->bytes_left == RIIC_INIT_MSG) {
  		riic->bytes_left = riic->msg->len;
  		readb(riic->base + RIIC_ICDRR);	/* dummy read */
  		return IRQ_HANDLED;
  	}
  
  	if (riic->bytes_left == 1) {
  		/* STOP must come before we set ACKBT! */
  		if (riic->is_last) {
  			riic_clear_set_bit(riic, 0, ICIER_SPIE, RIIC_ICIER);
  			writeb(ICCR2_SP, riic->base + RIIC_ICCR2);
  		}
  
  		riic_clear_set_bit(riic, 0, ICMR3_ACKBT, RIIC_ICMR3);
  
  	} else {
  		riic_clear_set_bit(riic, ICMR3_ACKBT, 0, RIIC_ICMR3);
  	}
  
  	/* Reading acks the RIE interrupt */
  	*riic->buf = readb(riic->base + RIIC_ICDRR);
  	riic->buf++;
  	riic->bytes_left--;
  
  	return IRQ_HANDLED;
  }
  
  static irqreturn_t riic_stop_isr(int irq, void *data)
  {
  	struct riic_dev *riic = data;
  
  	/* read back registers to confirm writes have fully propagated */
  	writeb(0, riic->base + RIIC_ICSR2);
  	readb(riic->base + RIIC_ICSR2);
  	writeb(0, riic->base + RIIC_ICIER);
  	readb(riic->base + RIIC_ICIER);
  
  	complete(&riic->msg_done);
  
  	return IRQ_HANDLED;
  }
  
  static u32 riic_func(struct i2c_adapter *adap)
  {
  	return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL;
  }
  
  static const struct i2c_algorithm riic_algo = {
  	.master_xfer	= riic_xfer,
  	.functionality	= riic_func,
  };
  
  static int riic_init_hw(struct riic_dev *riic, struct i2c_timings *t)
  {
  	int ret;
  	unsigned long rate;
  	int total_ticks, cks, brl, brh;
  
  	ret = clk_prepare_enable(riic->clk);
  	if (ret)
  		return ret;
  
  	if (t->bus_freq_hz > 400000) {
  		dev_err(&riic->adapter.dev,
  			"unsupported bus speed (%dHz). 400000 max\n",
  			t->bus_freq_hz);
  		clk_disable_unprepare(riic->clk);
  		return -EINVAL;
  	}
  
  	rate = clk_get_rate(riic->clk);
  
  	/*
  	 * Assume the default register settings:
  	 *  FER.SCLE = 1 (SCL sync circuit enabled, adds 2 or 3 cycles)
  	 *  FER.NFE = 1 (noise circuit enabled)
  	 *  MR3.NF = 0 (1 cycle of noise filtered out)
  	 *
  	 * Freq (CKS=000) = (I2CCLK + tr + tf)/ (BRH + 3 + 1) + (BRL + 3 + 1)
  	 * Freq (CKS!=000) = (I2CCLK + tr + tf)/ (BRH + 2 + 1) + (BRL + 2 + 1)
  	 */
  
  	/*
  	 * Determine reference clock rate. We must be able to get the desired
  	 * frequency with only 62 clock ticks max (31 high, 31 low).
  	 * Aim for a duty of 60% LOW, 40% HIGH.
  	 */
  	total_ticks = DIV_ROUND_UP(rate, t->bus_freq_hz);
  
  	for (cks = 0; cks < 7; cks++) {
  		/*
  		 * 60% low time must be less than BRL + 2 + 1
  		 * BRL max register value is 0x1F.
  		 */
  		brl = ((total_ticks * 6) / 10);
  		if (brl <= (0x1F + 3))
  			break;
  
  		total_ticks /= 2;
  		rate /= 2;
  	}
  
  	if (brl > (0x1F + 3)) {
  		dev_err(&riic->adapter.dev, "invalid speed (%lu). Too slow.\n",
  			(unsigned long)t->bus_freq_hz);
  		clk_disable_unprepare(riic->clk);
  		return -EINVAL;
  	}
  
  	brh = total_ticks - brl;
  
  	/* Remove automatic clock ticks for sync circuit and NF */
  	if (cks == 0) {
  		brl -= 4;
  		brh -= 4;
  	} else {
  		brl -= 3;
  		brh -= 3;
  	}
  
  	/*
  	 * Remove clock ticks for rise and fall times. Convert ns to clock
  	 * ticks.
  	 */
  	brl -= t->scl_fall_ns / (1000000000 / rate);
  	brh -= t->scl_rise_ns / (1000000000 / rate);
  
  	/* Adjust for min register values for when SCLE=1 and NFE=1 */
  	if (brl < 1)
  		brl = 1;
  	if (brh < 1)
  		brh = 1;
  
  	pr_debug("i2c-riic: freq=%lu, duty=%d, fall=%lu, rise=%lu, cks=%d, brl=%d, brh=%d\n",
  		 rate / total_ticks, ((brl + 3) * 100) / (brl + brh + 6),
  		 t->scl_fall_ns / (1000000000 / rate),
  		 t->scl_rise_ns / (1000000000 / rate), cks, brl, brh);
  
  	/* Changing the order of accessing IICRST and ICE may break things! */
  	writeb(ICCR1_IICRST | ICCR1_SOWP, riic->base + RIIC_ICCR1);
  	riic_clear_set_bit(riic, 0, ICCR1_ICE, RIIC_ICCR1);
  
  	writeb(ICMR1_CKS(cks), riic->base + RIIC_ICMR1);
  	writeb(brh | ICBR_RESERVED, riic->base + RIIC_ICBRH);
  	writeb(brl | ICBR_RESERVED, riic->base + RIIC_ICBRL);
  
  	writeb(0, riic->base + RIIC_ICSER);
  	writeb(ICMR3_ACKWP | ICMR3_RDRFS, riic->base + RIIC_ICMR3);
  
  	riic_clear_set_bit(riic, ICCR1_IICRST, 0, RIIC_ICCR1);
  
  	clk_disable_unprepare(riic->clk);
  
  	return 0;
  }
  
  static struct riic_irq_desc riic_irqs[] = {
  	{ .res_num = 0, .isr = riic_tend_isr, .name = "riic-tend" },
  	{ .res_num = 1, .isr = riic_rdrf_isr, .name = "riic-rdrf" },
  	{ .res_num = 2, .isr = riic_tdre_isr, .name = "riic-tdre" },
  	{ .res_num = 3, .isr = riic_stop_isr, .name = "riic-stop" },
  	{ .res_num = 5, .isr = riic_tend_isr, .name = "riic-nack" },
  };
  
  static int riic_i2c_probe(struct platform_device *pdev)
  {
  	struct riic_dev *riic;
  	struct i2c_adapter *adap;
  	struct resource *res;
  	struct i2c_timings i2c_t;
  	int i, ret;
  
  	riic = devm_kzalloc(&pdev->dev, sizeof(*riic), GFP_KERNEL);
  	if (!riic)
  		return -ENOMEM;
  
  	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
  	riic->base = devm_ioremap_resource(&pdev->dev, res);
  	if (IS_ERR(riic->base))
  		return PTR_ERR(riic->base);
  
  	riic->clk = devm_clk_get(&pdev->dev, NULL);
  	if (IS_ERR(riic->clk)) {
  		dev_err(&pdev->dev, "missing controller clock");
  		return PTR_ERR(riic->clk);
  	}
  
  	for (i = 0; i < ARRAY_SIZE(riic_irqs); i++) {
  		res = platform_get_resource(pdev, IORESOURCE_IRQ, riic_irqs[i].res_num);
  		if (!res)
  			return -ENODEV;
  
  		ret = devm_request_irq(&pdev->dev, res->start, riic_irqs[i].isr,
  					0, riic_irqs[i].name, riic);
  		if (ret) {
  			dev_err(&pdev->dev, "failed to request irq %s\n", riic_irqs[i].name);
  			return ret;
  		}
  	}
  
  	adap = &riic->adapter;
  	i2c_set_adapdata(adap, riic);
  	strlcpy(adap->name, "Renesas RIIC adapter", sizeof(adap->name));
  	adap->owner = THIS_MODULE;
  	adap->algo = &riic_algo;
  	adap->dev.parent = &pdev->dev;
  	adap->dev.of_node = pdev->dev.of_node;
  
  	init_completion(&riic->msg_done);
  
  	i2c_parse_fw_timings(&pdev->dev, &i2c_t, true);
  
  	ret = riic_init_hw(riic, &i2c_t);
  	if (ret)
  		return ret;
  
  
  	ret = i2c_add_adapter(adap);
  	if (ret)
  		return ret;
  
  	platform_set_drvdata(pdev, riic);
  
  	dev_info(&pdev->dev, "registered with %dHz bus speed\n",
  		 i2c_t.bus_freq_hz);
  	return 0;
  }
  
  static int riic_i2c_remove(struct platform_device *pdev)
  {
  	struct riic_dev *riic = platform_get_drvdata(pdev);
  
  	writeb(0, riic->base + RIIC_ICIER);
  	i2c_del_adapter(&riic->adapter);
  
  	return 0;
  }
  
  static const struct of_device_id riic_i2c_dt_ids[] = {
  	{ .compatible = "renesas,riic-rz" },
  	{ /* Sentinel */ },
  };
  
  static struct platform_driver riic_i2c_driver = {
  	.probe		= riic_i2c_probe,
  	.remove		= riic_i2c_remove,
  	.driver		= {
  		.name	= "i2c-riic",
  		.of_match_table = riic_i2c_dt_ids,
  	},
  };
  
  module_platform_driver(riic_i2c_driver);
  
  MODULE_DESCRIPTION("Renesas RIIC adapter");
  MODULE_AUTHOR("Wolfram Sang <wsa@sang-engineering.com>");
  MODULE_LICENSE("GPL v2");
  MODULE_DEVICE_TABLE(of, riic_i2c_dt_ids);
  