fix(plat/marvell/a3720/uart): fix UART clock rate value and divisor calculation

UART parent clock is by default the platform's xtal clock, which is
25 MHz.

The value defined in the driver, though, is 25.8048 MHz. This is a hack
for the suboptimal divisor calculation
  Divisor = UART clock / (16 * baudrate)
which does not use rounding division, resulting in a suboptimal value
for divisor if the correct parent clock rate was used.

Change the code for divisor calculation to
  Divisor = Round(UART clock / (16 * baudrate))
and change the parent clock rate value to 25 MHz.

The final UART divisor for default baudrate 115200 is not affected by
this change.

(Note that the parent clock rate should not be defined via a macro,
since the xtal clock can also be 40 MHz. This is outside of the scope of
this fix, though.)

Signed-off-by: Pali Rohár <pali@kernel.org>
Change-Id: Iaa401173df87aec94f2dd1b38a90fb6ed0bf0ec6

drivers/marvell/uart/a3700_console.S

@@ -45,8 +45,9 @@ func console_a3700_core_init
 	cbz	w2, init_fail
 
 	/* Program the baudrate */
-	/* Divisor =  Uart clock / (16 * baudrate) */
+	/* Divisor = Round(Uartclock / (16 * baudrate)) */
 	lsl	w2, w2, #4
+	add	w1, w1, w2, lsr #1
 	udiv	w2, w1, w2
 	and	w2, w2, #0x3ff
 

plat/marvell/armada/a3k/common/include/platform_def.h

@@ -164,7 +164,7 @@
  * PL011 related constants
  */
 #define PLAT_MARVELL_BOOT_UART_BASE		(MVEBU_REGS_BASE + 0x12000)
-#define PLAT_MARVELL_BOOT_UART_CLK_IN_HZ	25804800
+#define PLAT_MARVELL_BOOT_UART_CLK_IN_HZ	25000000
 
 #define PLAT_MARVELL_CRASH_UART_BASE		PLAT_MARVELL_BOOT_UART_BASE
 #define PLAT_MARVELL_CRASH_UART_CLK_IN_HZ	PLAT_MARVELL_BOOT_UART_CLK_IN_HZ