[PATCH v2 2/2] i2c: rcar: improve accuracy for R-Car Gen3+
From: Wolfram Sang
Date: Tue Sep 19 2023 - 11:20:07 EST
With some new registers, SCL can be calculated to be closer to the
desired rate. Apply the new formula for R-Car Gen3 device types.
Signed-off-by: Wolfram Sang <wsa+renesas@xxxxxxxxxxxxxxxxxxxx>
---
Changes since v1:
* fixed two whitespace issues
* use dedicated variables for scld and schd
* explicitly say "2 * smd" in the comment explaining the new formula
* use correct division 'clkp/SCL' in the same comment
* updated debug printout to use the new variables
For all of these, thanks Geert!
drivers/i2c/busses/i2c-rcar.c | 128 +++++++++++++++++++++++-----------
1 file changed, 89 insertions(+), 39 deletions(-)
diff --git a/drivers/i2c/busses/i2c-rcar.c b/drivers/i2c/busses/i2c-rcar.c
index bb4fc66309c2..b6b610011e84 100644
--- a/drivers/i2c/busses/i2c-rcar.c
+++ b/drivers/i2c/busses/i2c-rcar.c
@@ -41,6 +41,10 @@
#define ICSAR 0x1C /* slave address */
#define ICMAR 0x20 /* master address */
#define ICRXTX 0x24 /* data port */
+#define ICCCR2 0x28 /* Clock control 2 */
+#define ICMPR 0x2C /* SCL mask control */
+#define ICHPR 0x30 /* SCL HIGH control */
+#define ICLPR 0x34 /* SCL LOW control */
#define ICFBSCR 0x38 /* first bit setup cycle (Gen3) */
#define ICDMAER 0x3c /* DMA enable (Gen3) */
@@ -84,11 +88,25 @@
#define RMDMAE BIT(1) /* DMA Master Received Enable */
#define TMDMAE BIT(0) /* DMA Master Transmitted Enable */
+/* ICCCR2 */
+#define CDFD BIT(2) /* CDF Disable */
+#define HLSE BIT(1) /* HIGH/LOW Separate Control Enable */
+#define SME BIT(0) /* SCL Mask Enable */
+
/* ICFBSCR */
#define TCYC17 0x0f /* 17*Tcyc delay 1st bit between SDA and SCL */
#define RCAR_MIN_DMA_LEN 8
+/* SCL low/high ratio 5:4 to meet all I2C timing specs (incl safety margin) */
+#define RCAR_SCLD_RATIO 5
+#define RCAR_SCHD_RATIO 4
+/*
+ * SMD should be smaller than SCLD/SCHD and is always around 20 in the docs.
+ * Thus, we simply use 20 which works for low and high speeds.
+ */
+#define RCAR_DEFAULT_SMD 20
+
#define RCAR_BUS_PHASE_START (MDBS | MIE | ESG)
#define RCAR_BUS_PHASE_DATA (MDBS | MIE)
#define RCAR_BUS_PHASE_STOP (MDBS | MIE | FSB)
@@ -128,6 +146,8 @@ struct rcar_i2c_priv {
int pos;
u32 icccr;
+ u16 scld;
+ u16 schd;
u8 recovery_icmcr; /* protected by adapter lock */
enum rcar_i2c_type devtype;
struct i2c_client *slave;
@@ -216,11 +236,16 @@ static void rcar_i2c_init(struct rcar_i2c_priv *priv)
rcar_i2c_write(priv, ICMCR, MDBS);
rcar_i2c_write(priv, ICMSR, 0);
/* start clock */
- rcar_i2c_write(priv, ICCCR, priv->icccr);
-
- if (priv->devtype == I2C_RCAR_GEN3)
+ if (priv->devtype < I2C_RCAR_GEN3) {
+ rcar_i2c_write(priv, ICCCR, priv->icccr);
+ } else {
+ rcar_i2c_write(priv, ICCCR2, CDFD | HLSE | SME);
+ rcar_i2c_write(priv, ICCCR, priv->icccr);
+ rcar_i2c_write(priv, ICMPR, RCAR_DEFAULT_SMD);
+ rcar_i2c_write(priv, ICHPR, priv->schd);
+ rcar_i2c_write(priv, ICLPR, priv->scld);
rcar_i2c_write(priv, ICFBSCR, TCYC17);
-
+ }
}
static int rcar_i2c_bus_barrier(struct rcar_i2c_priv *priv)
@@ -241,7 +266,7 @@ static int rcar_i2c_bus_barrier(struct rcar_i2c_priv *priv)
static int rcar_i2c_clock_calculate(struct rcar_i2c_priv *priv)
{
- u32 scgd, cdf, round, ick, sum, scl, cdf_width;
+ u32 cdf, round, ick, sum, scl, cdf_width;
unsigned long rate;
struct device *dev = rcar_i2c_priv_to_dev(priv);
struct i2c_timings t = {
@@ -254,27 +279,17 @@ static int rcar_i2c_clock_calculate(struct rcar_i2c_priv *priv)
/* Fall back to previously used values if not supplied */
i2c_parse_fw_timings(dev, &t, false);
- switch (priv->devtype) {
- case I2C_RCAR_GEN1:
- cdf_width = 2;
- break;
- case I2C_RCAR_GEN2:
- case I2C_RCAR_GEN3:
- cdf_width = 3;
- break;
- default:
- dev_err(dev, "device type error\n");
- return -EIO;
- }
-
/*
* calculate SCL clock
* see
- * ICCCR
+ * ICCCR (and ICCCR2 for Gen3+)
*
* ick = clkp / (1 + CDF)
* SCL = ick / (20 + SCGD * 8 + F[(ticf + tr + intd) * ick])
*
+ * for Gen3+:
+ * SCL = clkp / (8 + SMD * 2 + SCLD + SCHD +F[(ticf + tr + intd) * clkp])
+ *
* ick : I2C internal clock < 20 MHz
* ticf : I2C SCL falling time
* tr : I2C SCL rising time
@@ -284,11 +299,12 @@ static int rcar_i2c_clock_calculate(struct rcar_i2c_priv *priv)
*/
rate = clk_get_rate(priv->clk);
cdf = rate / 20000000;
- if (cdf >= 1U << cdf_width) {
- dev_err(dev, "Input clock %lu too high\n", rate);
- return -EIO;
- }
- ick = rate / (cdf + 1);
+ cdf_width = (priv->devtype == I2C_RCAR_GEN1) ? 2 : 3;
+ if (cdf >= 1U << cdf_width)
+ goto err_no_val;
+
+ /* On Gen3+, we use cdf only for the filters, not as a SCL divider */
+ ick = rate / (priv->devtype < I2C_RCAR_GEN3 ? (cdf + 1) : 1);
/*
* It is impossible to calculate a large scale number on u32. Separate it.
@@ -301,24 +317,58 @@ static int rcar_i2c_clock_calculate(struct rcar_i2c_priv *priv)
round = DIV_ROUND_CLOSEST(ick, 1000000);
round = DIV_ROUND_CLOSEST(round * sum, 1000);
- /*
- * SCL = ick / (20 + 8 * SCGD + F[(ticf + tr + intd) * ick])
- * 20 + 8 * SCGD + F[...] = ick / SCL
- * SCGD = ((ick / SCL) - 20 - F[...]) / 8
- * Result (= SCL) should be less than bus_speed for hardware safety
- */
- scgd = DIV_ROUND_UP(ick, t.bus_freq_hz ?: 1);
- scgd = DIV_ROUND_UP(scgd - 20 - round, 8);
- scl = ick / (20 + 8 * scgd + round);
+ if (priv->devtype < I2C_RCAR_GEN3) {
+ u32 scgd;
+ /*
+ * SCL = ick / (20 + 8 * SCGD + F[(ticf + tr + intd) * ick])
+ * 20 + 8 * SCGD + F[...] = ick / SCL
+ * SCGD = ((ick / SCL) - 20 - F[...]) / 8
+ * Result (= SCL) should be less than bus_speed for hardware safety
+ */
+ scgd = DIV_ROUND_UP(ick, t.bus_freq_hz ?: 1);
+ scgd = DIV_ROUND_UP(scgd - 20 - round, 8);
+ scl = ick / (20 + 8 * scgd + round);
- if (scgd > 0x3f)
- goto err_no_val;
+ if (scgd > 0x3f)
+ goto err_no_val;
- dev_dbg(dev, "clk %u/%u(%lu), round %u, CDF: %u, SCGD: %u\n",
- scl, t.bus_freq_hz, rate, round, cdf, scgd);
+ dev_dbg(dev, "clk %u/%u(%lu), round %u, CDF: %u, SCGD: %u\n",
+ scl, t.bus_freq_hz, rate, round, cdf, scgd);
- /* keep icccr value */
- priv->icccr = scgd << cdf_width | cdf;
+ priv->icccr = scgd << cdf_width | cdf;
+ } else {
+ u32 x, sum_ratio = RCAR_SCHD_RATIO + RCAR_SCLD_RATIO;
+ /*
+ * SCLD/SCHD ratio and SMD default value are explained above
+ * where they are defined. With these definitions, we can compute
+ * x as a base value for the SCLD/SCHD ratio:
+ *
+ * SCL = clkp / (8 + 2 * SMD + SCLD + SCHD + F[(ticf + tr + intd) * clkp])
+ * SCL = clkp / (8 + 2 * RCAR_DEFAULT_SMD + RCAR_SCLD_RATIO * x
+ * + RCAR_SCHD_RATIO * x + F[...])
+ *
+ * with: sum_ratio = RCAR_SCLD_RATIO + RCAR_SCHD_RATIO
+ * and: smd = RCAR_DEFAULT_SMD
+ *
+ * SCL = clkp / (8 + 2 * smd + sum_ratio * x + F[...])
+ * 8 + 2 * smd + sum_ratio * x + F[...] = clkp / SCL
+ * x = ((clkp / SCL) - 8 - 2 * smd - F[...]) / sum_ratio
+ */
+ x = DIV_ROUND_UP(rate, t.bus_freq_hz ?: 1);
+ x = DIV_ROUND_UP(x - 8 - 2 * RCAR_DEFAULT_SMD - round, sum_ratio);
+ scl = rate / (8 + 2 * RCAR_DEFAULT_SMD + sum_ratio * x + round);
+
+ /* Bail out if values don't fit into 16 bit or SMD became too large */
+ if (x * RCAR_SCLD_RATIO > 0xffff || RCAR_DEFAULT_SMD > x * RCAR_SCHD_RATIO)
+ goto err_no_val;
+
+ priv->icccr = cdf;
+ priv->scld = RCAR_SCLD_RATIO * x;
+ priv->schd = RCAR_SCHD_RATIO * x;
+
+ dev_dbg(dev, "clk %u/%u(%lu), round %u, CDF: %u SCLD %u SCHD %u\n",
+ scl, t.bus_freq_hz, rate, round, cdf, priv->scld, priv->schd);
+ }
return 0;
--
2.35.1