On Wed, 29 Apr 2026, Jia Wang wrote:

> 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),

Thanks for doing this, it's just so much better than the original. :-)

>  	.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)))

Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>

-- 
 i.