[U-Boot] x86: Bay Trail support with W83627DHG

[Stefan Roese <sr@denx.de>]

Hi Simon, Hi Bin!

I'm currently busy with porting U-Boot to a Bay Trail board.
Equipped with an Intel Atom E3845 and additionally the
Nuvoton / Winbond W83627DHG Super IO chip.

My staring point for this port is the Minnowboard MAX, which
works very well btw. I've used the same binaries as described
in the README.x86 as on the MinnowMAX for this new Bay Trail
board. But am not able yet to see any output on the DEBUG_UART.

Bin, you already mentioned in a previous mail, that I need to
enable the legacy UART in the Super IO chip for this. I've
started adding a small driver for this, similar to the one
you've introduced for the SMSC:

--<--------
#define WINBOND_ENTRY_KEY	0x87
#define WINBOND_EXIT_KEY	0xAA

/* Enable configuration: pass entry key '0x87' into index port dev. */
static void pnp_enter_conf_state(u16 dev)
{
	u16 port = dev >> 8;

	outb(WINBOND_ENTRY_KEY, port);
	outb(WINBOND_ENTRY_KEY, port);
}

/* Disable configuration: pass exit key '0xAA' into index port dev. */
static void pnp_exit_conf_state(u16 dev)
{
	u16 port = dev >> 8;

	outb(WINBOND_EXIT_KEY, port);
}

/* Bring up early serial debugging output before the RAM is initialized. */
void winbond_enable_serial(uint dev, uint iobase, uint irq)
{
	pnp_enter_conf_state(dev);
	pnp_set_logical_device(dev);
	pnp_set_enable(dev, 0);
	pnp_set_iobase(dev, PNP_IDX_IO0, iobase);
	pnp_set_irq(dev, PNP_IDX_IRQ0, irq);
	pnp_set_enable(dev, 1);
	pnp_exit_conf_state(dev);
}
--<--------

This is called via:
--<--------
/* I/O address of Winbond Super IO chip */
#define WINBOND_IO_PORT		0x2e

/* Logical device number */
#define W83627DHG_SP1		2	/* Com1 */

	winbond_enable_serial(PNP_DEV(WINBOND_IO_PORT, W83627DHG_SP1),
			      UART0_BASE, UART0_IRQ);
--<--------

As you may notice, this is ported from coreboot. But still, this
is not enough to get some output on the UART.

Debugging (without JTAG debugger and without DEBUG_UART but with
POST output) shows, that the board hangs somewhere in the FSP code.
When called via fsp_init(). POST shows 0x2A in this case. And
FSP does not return to fsp_continue()@all.

Do you have any hints what could be missing for the DEBUG
UART to work on this board? Or what might cause the board
to hang in the FSP code? Or what the meaning of the FSP 0x2A
POST code is?

Thanks,
Stefan