[PATCH v2 2/2] serial: 8250_ingenic: Set UMR and UACR at probe

[Olivier Louvignes]

Ingenic UARTs have two registers beyond the 16550's: UMR, the number of
clocks a bit takes, and UACR, which adds one clock to chosen bits of a
frame, for fractional baud rates. The JZ4725, JZ4740, JZ4755, JZ4760,
X1000, X1830, X2000 and X1600 programming manuals all have them at 0x24
and 0x28. The divisor the 8250 core computes assumes 16 clocks a bit and
none added.

The driver never writes them, so a UART keeps whatever was there before.
On a HiBy R1 (X1600) the vendor boot loader sets UMR to 8 on its console
UART, and the vendor kernel had left 8 on UART0, which carries the
Bluetooth chip: every rate came out doubled, and the chip never answered
("command 0xfc18 tx timeout" from hci_bcm). Their reset value, 0, which
the X1000 and X1600 manuals call normal mode, does not work on the X1600
either: with UMR at 0 the same command times out.

Set UMR to 16 and UACR to 0 at probe.

Tested on a HiBy R1: with UMR at 0 or 8 the BCM43430A1 on UART0 fails to
set up; with this patch it comes up at 1.5 Mbaud and streams A2DP audio.

Signed-off-by: Olivier Louvignes <olivier@xxxxxxxxx>
---
 drivers/tty/serial/8250/8250_ingenic.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/tty/serial/8250/8250_ingenic.c b/drivers/tty/serial/8250/8250_ingenic.c
index 0cdadacd7019..ca45e74b999b 100644
--- a/drivers/tty/serial/8250/8250_ingenic.c
+++ b/drivers/tty/serial/8250/8250_ingenic.c
@@ -40,6 +40,10 @@ static const struct of_device_id of_match[];
 #define UART_MCR_MDCE	BIT(7)
 #define UART_MCR_FCM	BIT(6)
 
+/* Clocks a bit, and an extra clock for chosen bits */
+#define UART_UMR	9
+#define UART_UACR	10
+
 static struct earlycon_device *early_device;
 
 static uint8_t early_in(struct uart_port *port, int offset)
@@ -298,6 +302,14 @@ static int ingenic_uart_probe(struct platform_device *pdev)
 	}
 	uart.port.uartclk = clk_get_rate(data->clk_baud);
 
+	/*
+	 * The 8250 core's divisor assumes 16 clocks a bit. Whatever ran before
+	 * may have left another count, and on the X1600 even the reset value,
+	 * 0, does not give 16.
+	 */
+	writel(16, uart.port.membase + (UART_UMR << uart.port.regshift));
+	writel(0, uart.port.membase + (UART_UACR << uart.port.regshift));
+
 	data->uport = serial8250_register_8250_port(&uart);
 	if (IS_ERR(data->uport)) {
 		err = PTR_ERR(data->uport);
-- 
2.39.5