[U-Boot] [PATCH v2] serial: ns16550: Add register shift variable

[Felix Brack]

This patch adds a new Kconfig variable that allows setting
the register offset 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
(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>
---

Changes in v2:
- clarify variable usage
- set default value to 2 for AM33XX SoC

 drivers/serial/Kconfig   | 15 +++++++++++++++
 drivers/serial/ns16550.c |  3 ++-
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/drivers/serial/Kconfig b/drivers/serial/Kconfig
index 766e5ce..7eb3c6f 100644
--- a/drivers/serial/Kconfig
+++ b/drivers/serial/Kconfig
@@ -530,6 +530,21 @@ 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 "Amount of bits to shift register offsets left"
+	default 2 if AM33XX
+	default 0
+	depends on SYS_NS16550
+	help
+	  Use this to specify the amount of bits to shift device register
+	  offsets to the left. The resulting register offset is calculate as
+	  follows: "reg offset" << SYS_NS16550_REG_SHIFT. If, for example,
+	  the device register offsets are 0x00, 0x04, 0x08, 0x0C and so forth
+	  than set this to 2.
+	  In case of AM33XX SoC the default value is 2, 0 otherwise. 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) {
-- 
2.7.4