[PATCH v5 2/4] serial: 8250_dw: build Renesas RZN1 CPR value from DW_UART_CPR_* definitions

Jia Wang
2026-04-28T05:26:56Z

Replace the magic CPR value for Renesas RZ/N1 with a composition using
DW_UART_CPR_* bit/field definitions and FIELD_PREP_CONST().

Introduce a helper macro to convert a FIFO size (bytes) into the CPR
FIFO_MODE field value, with BUILD_BUG_ON_ZERO() checks for alignment and
bounds. Use it to replace the literal FIFO_MODE values in the RZN1.

Signed-off-by: Jia Wang <wangjia@ultrarisc.com>
---
drivers/tty/serial/8250/8250_dw.c | 11 ++++++++++-
drivers/tty/serial/8250/8250_dwlib.h | 7 +++++++
2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c
index 467755bf0092..5cf3bb74b285 100644
--- a/drivers/tty/serial/8250/8250_dw.c
+++ b/drivers/tty/serial/8250/8250_dw.c
@@ -937,7 +937,16 @@ static const struct dw8250_platform_data dw8250_armada_38x_data = {

static const struct dw8250_platform_data dw8250_renesas_rzn1_data = {
.usr_reg = DW_UART_USR,
- .cpr_value = 0x00012f32,
+ .cpr_value = FIELD_PREP_CONST(DW_UART_CPR_ABP_DATA_WIDTH, 2) |
+ DW_UART_CPR_AFCE_MODE |
+ DW_UART_CPR_THRE_MODE |
+ DW_UART_CPR_ADDITIONAL_FEATURES |
+ DW_UART_CPR_FIFO_ACCESS |
+ DW_UART_CPR_FIFO_STAT |
+ DW_UART_CPR_SHADOW |
+ DW_UART_CPR_DMA_EXTRA |
+ FIELD_PREP_CONST(DW_UART_CPR_FIFO_MODE,
+ DW_UART_CPR_FIFO_MODE_FROM_SIZE(16)),
.quirks = DW_UART_QUIRK_CPR_VALUE | DW_UART_QUIRK_IS_DMA_FC,
};

diff --git a/drivers/tty/serial/8250/8250_dwlib.h b/drivers/tty/serial/8250/8250_dwlib.h
index 2f26f9ecacbe..c1f87cd42ecc 100644
--- a/drivers/tty/serial/8250/8250_dwlib.h
+++ b/drivers/tty/serial/8250/8250_dwlib.h
@@ -6,6 +6,8 @@

#include <linux/bitfield.h>
#include <linux/bits.h>
+#include <linux/build_bug.h>
+#include <linux/align.h>
#include <linux/io.h>
#include <linux/types.h>

@@ -70,6 +72,11 @@

/* Helper for FIFO size calculation */
#define DW_UART_CPR_FIFO_SIZE(a) (FIELD_GET(DW_UART_CPR_FIFO_MODE, (a)) * 16)
+#define DW_UART_CPR_FIFO_MODE_MAX 0x80
+#define DW_UART_CPR_FIFO_MODE_FROM_SIZE(size) \
+ (BUILD_BUG_ON_ZERO(!IS_ALIGNED((size), 16)) + \
+ BUILD_BUG_ON_ZERO(((size) / 16) > DW_UART_CPR_FIFO_MODE_MAX) + \
+ ((size) / 16))

struct dw8250_port_data {
/* Port properties */

--
2.34.1