i2c: designware: Replace magic numbers with named constants

Replace various magic numbers with properly named constants to improve
code readability and maintainability. This includes constants for
register access, timing adjustments, timeouts, FIFO parameters,
and default values.

This makes the code more self-documenting without altering any
functionality.

Signed-off-by: Artem Shimko <a.shimko.dev@gmail.com>
Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>
Link: https://lore.kernel.org/r/20251211122947.1469666-1-a.shimko.dev@gmail.com

Author: Artem Shimko

drivers/i2c/busses/i2c-designware-common.c

@@ -12,6 +12,7 @@
 #define DEFAULT_SYMBOL_NAMESPACE	"I2C_DW_COMMON"
 
 #include <linux/acpi.h>
+#include <linux/bitfield.h>
 #include <linux/clk.h>
 #include <linux/delay.h>
 #include <linux/device.h>
@@ -34,6 +35,10 @@
 
 #include "i2c-designware-core.h"
 
+#define DW_IC_DEFAULT_BUS_CAPACITANCE_pF	100
+#define DW_IC_ABORT_TIMEOUT_US			10
+#define DW_IC_BUSY_POLL_TIMEOUT_US		(1 * USEC_PER_MSEC)
+
 static const char *const abort_sources[] = {
 	[ABRT_7B_ADDR_NOACK] =
 		"slave address not acknowledged (7bit mode)",
@@ -106,7 +111,7 @@ static int dw_reg_read_word(void *context, unsigned int reg, unsigned int *val)
 	struct dw_i2c_dev *dev = context;
 
 	*val = readw(dev->base + reg) |
-		(readw(dev->base + reg + 2) << 16);
+		(readw(dev->base + reg + DW_IC_REG_STEP_BYTES) << DW_IC_REG_WORD_SHIFT);
 
 	return 0;
 }
@@ -116,7 +121,7 @@ static int dw_reg_write_word(void *context, unsigned int reg, unsigned int val)
 	struct dw_i2c_dev *dev = context;
 
 	writew(val, dev->base + reg);
-	writew(val >> 16, dev->base + reg + 2);
+	writew(val >> DW_IC_REG_WORD_SHIFT, dev->base + reg + DW_IC_REG_STEP_BYTES);
 
 	return 0;
 }
@@ -165,7 +170,7 @@ int i2c_dw_init_regmap(struct dw_i2c_dev *dev)
 	if (reg == swab32(DW_IC_COMP_TYPE_VALUE)) {
 		map_cfg.reg_read = dw_reg_read_swab;
 		map_cfg.reg_write = dw_reg_write_swab;
-	} else if (reg == (DW_IC_COMP_TYPE_VALUE & 0x0000ffff)) {
+	} else if (reg == lower_16_bits(DW_IC_COMP_TYPE_VALUE)) {
 		map_cfg.reg_read = dw_reg_read_word;
 		map_cfg.reg_write = dw_reg_write_word;
 	} else if (reg != DW_IC_COMP_TYPE_VALUE) {
@@ -384,7 +389,7 @@ int i2c_dw_fw_parse_and_configure(struct dw_i2c_dev *dev)
 	i2c_parse_fw_timings(device, t, false);
 
 	if (device_property_read_u32(device, "snps,bus-capacitance-pf", &dev->bus_capacitance_pF))
-		dev->bus_capacitance_pF = 100;
+		dev->bus_capacitance_pF = DW_IC_DEFAULT_BUS_CAPACITANCE_pF;
 
 	dev->clk_freq_optimized = device_property_read_bool(device, "snps,clk-freq-optimized");
 
@@ -539,8 +544,9 @@ void __i2c_dw_disable(struct dw_i2c_dev *dev)
 
 		regmap_write(dev->map, DW_IC_ENABLE, enable | DW_IC_ENABLE_ABORT);
 		ret = regmap_read_poll_timeout(dev->map, DW_IC_ENABLE, enable,
-					       !(enable & DW_IC_ENABLE_ABORT), 10,
-					       100);
+					       !(enable & DW_IC_ENABLE_ABORT),
+					       DW_IC_ABORT_TIMEOUT_US,
+					       10 * DW_IC_ABORT_TIMEOUT_US);
 		if (ret)
 			dev_err(dev->dev, "timeout while trying to abort current transfer\n");
 	}
@@ -552,7 +558,7 @@ void __i2c_dw_disable(struct dw_i2c_dev *dev)
 		 * in that case this test reads zero and exits the loop.
 		 */
 		regmap_read(dev->map, DW_IC_ENABLE_STATUS, &status);
-		if ((status & 1) == 0)
+		if (!(status & 1))
 			return;
 
 		/*
@@ -635,7 +641,8 @@ int i2c_dw_wait_bus_not_busy(struct dw_i2c_dev *dev)
 
 	ret = regmap_read_poll_timeout(dev->map, DW_IC_STATUS, status,
 				       !(status & DW_IC_STATUS_ACTIVITY),
-				       1100, 20000);
+				       DW_IC_BUSY_POLL_TIMEOUT_US,
+				       20 * DW_IC_BUSY_POLL_TIMEOUT_US);
 	if (ret) {
 		dev_warn(dev->dev, "timeout waiting for bus ready\n");
 
@@ -699,12 +706,12 @@ int i2c_dw_set_fifo_size(struct dw_i2c_dev *dev)
 	if (ret)
 		return ret;
 
-	tx_fifo_depth = ((param >> 16) & 0xff) + 1;
-	rx_fifo_depth = ((param >> 8)  & 0xff) + 1;
+	tx_fifo_depth = FIELD_GET(DW_IC_FIFO_TX_FIELD, param) + 1;
+	rx_fifo_depth = FIELD_GET(DW_IC_FIFO_RX_FIELD, param) + 1;
 	if (!dev->tx_fifo_depth) {
 		dev->tx_fifo_depth = tx_fifo_depth;
 		dev->rx_fifo_depth = rx_fifo_depth;
-	} else if (tx_fifo_depth >= 2) {
+	} else if (tx_fifo_depth >= DW_IC_FIFO_MIN_DEPTH) {
 		dev->tx_fifo_depth = min_t(u32, dev->tx_fifo_depth,
 				tx_fifo_depth);
 		dev->rx_fifo_depth = min_t(u32, dev->rx_fifo_depth,

drivers/i2c/busses/i2c-designware-core.h

@@ -41,6 +41,19 @@
 #define DW_IC_DATA_CMD_DAT			GENMASK(7, 0)
 #define DW_IC_DATA_CMD_FIRST_DATA_BYTE		BIT(11)
 
+/*
+ * Register access parameters
+ */
+#define DW_IC_REG_STEP_BYTES			2
+#define DW_IC_REG_WORD_SHIFT			16
+
+/*
+ * FIFO depth configuration
+ */
+#define DW_IC_FIFO_TX_FIELD			GENMASK(23, 16)
+#define DW_IC_FIFO_RX_FIELD			GENMASK(15, 8)
+#define DW_IC_FIFO_MIN_DEPTH			2
+
 /*
  * Registers offset
  */