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.

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

Signed-off-by: Artem Shimko <a.shimko.dev@gmail.com>
---
Hello maintainers and reviewers,

Fix replaces magic numbers throughout the DesignWare I2C driver with named 
constants to improve code readability and maintainability.

The change introduces constants for register access, timing adjustments, 
timeouts, FIFO parameters, and default values, all properly documented 
with comments.

No functional changes.

Thank you for your consideration.
--
Regards,
Artem

ChangeLog:
  v1:
    * https://lore.kernel.org/all/20251105161845.2535367-1-a.shimko.dev@gmail.com/T/#u
  v2:
    * https://lore.kernel.org/all/20251106160206.2617785-1-a.shimko.dev@gmail.com/T/#u
  v3:
    * Add missing include for linux/bitfield.h

 drivers/i2c/busses/i2c-designware-common.c | 33 ++++++++++++++--------
 drivers/i2c/busses/i2c-designware-core.h   | 13 +++++++++
 2 files changed, 35 insertions(+), 11 deletions(-)

diff --git a/drivers/i2c/busses/i2c-designware-common.c b/drivers/i2c/busses/i2c-designware-common.c
index 5b1e8f74c4ac..3bc55068da03 100644
--- a/drivers/i2c/busses/i2c-designware-common.c
+++ b/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 +35,14 @@
 
 #include "i2c-designware-core.h"
 
+#define DW_IC_DEFAULT_BUS_CAPACITANCE_PF	100
+
+#define DW_IC_ABORT_TIMEOUT_US			10
+#define DW_IC_ABORT_TOTAL_TIMEOUT_US		100
+
+#define DW_IC_BUSY_POLL_TIMEOUT_US		1100
+#define DW_IC_BUSY_TOTAL_TIMEOUT_US		20000
+
 static const char *const abort_sources[] = {
 	[ABRT_7B_ADDR_NOACK] =
 		"slave address not acknowledged (7bit mode)",
@@ -106,7 +115,7 @@ 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 +125,7 @@ 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 +174,7 @@ 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 +393,7 @@ 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 +548,9 @@ 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,
+					       DW_IC_ABORT_TOTAL_TIMEOUT_US);
 		if (ret)
 			dev_err(dev->dev, "timeout while trying to abort current transfer\n");
 	}
@@ -552,7 +562,7 @@ 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 +645,8 @@ 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,
+				       DW_IC_BUSY_TOTAL_TIMEOUT_US);
 	if (ret) {
 		dev_warn(dev->dev, "timeout waiting for bus ready\n");
 
@@ -699,12 +710,12 @@ 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,
diff --git a/drivers/i2c/busses/i2c-designware-core.h b/drivers/i2c/busses/i2c-designware-core.h
index 347843b4f5dd..a699953bf5ae 100644
--- a/drivers/i2c/busses/i2c-designware-core.h
+++ b/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
  */
-- 
2.43.0

On Thu, Dec 04, 2025 at 07:13:08PM +0300, Artem Shimko wrote:
> 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.
> 
> The change makes the code more self-documenting without altering any

s/The change/This/

> functionality.

...

> +#define DW_IC_DEFAULT_BUS_CAPACITANCE_PF	100

_pF

(yes, it's fine to use CamelCase for unit suffixes, some of them historically
 use capital letters, but it's better to follow the actual unit spelling from
 Système International d'Unité)

> +#define DW_IC_ABORT_TIMEOUT_US			10

> +#define DW_IC_ABORT_TOTAL_TIMEOUT_US		100

Those TOTAL are not needed, just use a multiplier in place, this will be
basically the explicit number of "iterations" (yes, I know that the real
ones are 2x or 4x more).

> +#define DW_IC_BUSY_POLL_TIMEOUT_US		1100

Why not 1000?

(Yeah, I see the original value, but I think it makes no sense to go
 specifically with 1100).

And in this case it might be better to write it as (1 * USEC_PER_MSEC)
which makes it easier to get that this is 1 millisecond (in µs units).

-- 
With Best Regards,
Andy Shevchenko