8250 UART doesn't work

From: Woody Wu
Date: Thu Dec 06 2012 - 02:56:14 EST

Hi, list

Does anyone here familiar to the serial 8250 driver?

I enabled two uart ports in my board definition, but the ports doesn't
appear after I loaded the kernel (3.4.19). I discovered, it failed at
the UART port auto configuration stage, the exact function is
autoconfig(...) in drivers/tty/serial/8250.c.

if (!(port->flags & UPF_BUGGY_UART)) {
scratch = serial_in(up, UART_IER);
serial_out(up, UART_IER, 0);
#ifdef __i386__
outb(0xff, 0x080);
* Mask out IER[7:4] bits for test as some UARTs (e.g. TL
* 16C754B) allow only to modify them if an EFR bit is set.
scratch2 = serial_in(up, UART_IER) & 0x0f;
serial_out(up, UART_IER, 0x0F);
#ifdef __i386__
outb(0, 0x080);
scratch3 = serial_in(up, UART_IER) & 0x0f;
serial_out(up, UART_IER, scratch);
if (scratch2 != 0 || scratch3 != 0x0F) {
* We failed; there's nothing here
DEBUG_AUTOCONF("IER test failed (%02x, %02x) ",
scratch2, scratch3);
goto out;

By enabling the debug output, I found it failed because values in scratch2 and
scratch3 are all zeros.

In my board definition, what I configured are something like:

#define SERIAL_BASE (0xe1400000)
#define SERIAL_CLK (14745600)

static struct plat_serial8250_port lgf2410_urts_data[] = {
[0] = {
.mapbase = SERIAL_BASE + 0x00,
.irq = 16,
.flags = SERIAL_FLAGS,
.iotype = UPIO_MEM,
.regshift = 0,
.uartclk = SERIAL_CLK,
[1] = {
.mapbase = SERIAL_BASE + 0x10,
.irq = 17,
.flags = SERIAL_FLAGS,
.iotype = UPIO_MEM,
.regshift = 0,
.uartclk = SERIAL_CLK,

static struct platform_device lgf2410_urts = {
.name = "serial8250",
.dev = {
.platform_data = &lgf2410_urts_data,

I think the mapbase addresses are corrected. Since I copied these addresse from
a old kernel log output from a 2.6.16 linux. For the old 2.6.16 kernel, which
run the exact same board, I have no information how it was configured.

Below is the 2.6.16 kernel output, it successfully detected the UART

serial8250: tts0 at MMIO 0xe1400000 (irq = 16) is a 16550A
serial8250: tts1 at MMIO 0xe1400008 (irq = 16) is a 16550A
serial8250: tts2 at MMIO 0xe1400010 (irq = 17) is a 16550A
serial8250: tts3 at MMIO 0xe1400018 (irq = 17) is a 16550A

Now I expect the same result from my self tailored 3.4.19 kernel.

Hope I can get your kind support! Thanks.

I can't go back to yesterday - because I was a different person then.

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