[U-Boot] [PATCH] serial: ns16550: Add register shift variable

[Alexander Graf]

On 07/13/2018 04:43 PM, Felix Brack wrote:
> This patch adds a new Kconfig variable that allows setting
> the register shift value for the ns16550 driver to some other
> value then 0 if not defined by the DT. All credit for this
> patch goes to Lokesh Vutla as it was his idea.
>
> The motivation for writing this patch originates in the
> effort of synchronizing U-Boot DT to Linux DT for am33xx SOCs.
> The current am33xx.dtsi file from U-Boot defines the <reg-shift>
> property for all UART nodes. The actual (4.18+) am33xx.dtsi
> file from Linux does not define <reg-shift> anymore. To prevent

How does Linux determine the shift value then?


Alex

> (probably difficult) changes in many .dts and .dtsi files once
> the synchronization is done, one can use this new variable. For
> the pdu001 board, for example, SYS_NS16550_REG_SHIFT is set
> to 2; no need to clutter U-Boot and board specific dts files
> with <reg-shift> properties.
>
> Signed-off-by: Felix Brack <fb at ltec.ch>
> ---
>
>   drivers/serial/Kconfig   | 12 ++++++++++++
>   drivers/serial/ns16550.c |  3 ++-
>   2 files changed, 14 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/serial/Kconfig b/drivers/serial/Kconfig
> index 766e5ce..c80ad4d 100644
> --- a/drivers/serial/Kconfig
> +++ b/drivers/serial/Kconfig
> @@ -530,6 +530,18 @@ config SYS_NS16550
>   	  be used. It can be a constant or a function to get clock, eg,
>   	  get_serial_clock().
>   
> +config SYS_NS16550_REG_SHIFT
> +	int "Number of bytes to shift register offsets"
> +	default 0
> +	depends on SYS_NS16550
> +	help
> +	  Use this to specify the amount of bytes between discrete
> +	  device registers. If, for example, the device registers are
> +	  located at 0x00, 0x04, 0x08, 0x0C and so forth than set
> +	  this to 2. The default value is 0.
> +	  Note that a <reg-shift> property defined in a UART node of
> +	  the device tree will always take precedence.
> +
>   config INTEL_MID_SERIAL
>   	bool "Intel MID platform UART support"
>   	depends on DM_SERIAL && OF_CONTROL
> diff --git a/drivers/serial/ns16550.c b/drivers/serial/ns16550.c
> index 9c80090..9ff6dbe 100644
> --- a/drivers/serial/ns16550.c
> +++ b/drivers/serial/ns16550.c
> @@ -442,7 +442,8 @@ int ns16550_serial_ofdata_to_platdata(struct udevice *dev)
>   #endif
>   
>   	plat->reg_offset = dev_read_u32_default(dev, "reg-offset", 0);
> -	plat->reg_shift = dev_read_u32_default(dev, "reg-shift", 0);
> +	plat->reg_shift = dev_read_u32_default(dev, "reg-shift",
> +					       CONFIG_SYS_NS16550_REG_SHIFT);
>   
>   	err = clk_get_by_index(dev, 0, &clk);
>   	if (!err) {