[PATCH v7 2/4] serial: 8250_dw: build Renesas RZN1 CPR value from DW_UART_CPR_* definitions

[Jia Wang <wangjia@ultrarisc.com>]

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    | 10 +++++++++-
 drivers/tty/serial/8250/8250_dwlib.h |  8 +++++++-
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c
index 467755bf0092..480f82d89856 100644
--- a/drivers/tty/serial/8250/8250_dw.c
+++ b/drivers/tty/serial/8250/8250_dw.c
@@ -937,7 +937,15 @@ 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 |
+		     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..1fe52332e774 100644
--- a/drivers/tty/serial/8250/8250_dwlib.h
+++ b/drivers/tty/serial/8250/8250_dwlib.h
@@ -6,6 +6,7 @@
 
 #include <linux/bitfield.h>
 #include <linux/bits.h>
+#include <linux/build_bug.h>
 #include <linux/io.h>
 #include <linux/types.h>
 
@@ -68,8 +69,13 @@
 #define DW_UART_CPR_DMA_EXTRA		BIT(13)
 #define DW_UART_CPR_FIFO_MODE		GENMASK(23, 16)
 
-/* Helper for FIFO size calculation */
+/* Helpers 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_FROM_SIZE(size)			\
+	(FIELD_PREP_CONST(DW_UART_CPR_FIFO_MODE,		\
+			  BUILD_BUG_ON_ZERO((size) > 2048) +	\
+			  BUILD_BUG_ON_ZERO((size) % 16) +	\
+			  ((size) / 16)))
 
 struct dw8250_port_data {
 	/* Port properties */

-- 
2.34.1