[U-Boot] Configuring BRGs and BRG input clock on an MPC875

[Mikhail Zaturenskiy]

> Anybody have an idea as to what I'm doing wrong? Could there be
> something wrong with my CLK2?

Once again I'm going to answer my own question. The problem WAS with
CLK2 not being properly initialized. I had to do the following to get
everything working:

1. To get BRG1 to use CLK2, made change to "serial_setdivisor"
function in cpu/mpc8xx/serial.c:
************************************************************************
static void serial_setdivisor(volatile cpm8xx_t *cp) {
// MZ - Note: the CONFIG_USE_CLK2 flag is invented by me to allow the
BRG input clock to be CLK2

#if defined CONFIG_USE_CLK2
	// MZ - CLK2 is 48MHz
	// - Note: divisor = 26 at 115200bps
	// - Note: divisor = 52 at 57600bps
	int divisor=(48000000 + 8*gd->baudrate)/16/gd->baudrate;
#else
	// MZ
	// - Note: divisor = 71 at 130MHz and 115200bps
	// - Note: divisor = 141 at 130MHz and 57600bps
	int divisor=(gd->cpu_clk + 8*gd->baudrate)/16/gd->baudrate;
#endif
	
	if(divisor/16>0x1000) {
		/* bad divisor, assume 50MHz clock and 9600 baud */
		divisor=(50*1000*1000 + 8*9600)/16/9600;
	}

#ifdef CONFIG_SYS_BRGCLK_PRESCALE
	divisor /= CONFIG_SYS_BRGCLK_PRESCALE;
#endif

	if(divisor<=0x1000) {
		cp->cp_brgc1=((divisor-1)<<1) | CPM_BRG_EN;
	} else {
		cp->cp_brgc1=((divisor/16-1)<<1) | CPM_BRG_EN | CPM_BRG_DIV16;
	}

#if defined CONFIG_USE_CLK2
	// MZ - switching BRG1 input clock to CLK2
	cp->cp_brgc1 |= CPM_BRG_EXTC_CLK2;
#endif
}
******************************************************************************

2. To get BRG4 to use CLK2 and to set SCC4 to use BRG4 (decided to use
BRG4 for SCC4 instead of BRG2), I made change to "board_early_init_f"
in my board's board/ops1/ops1.c file:
******************************************************************************
int board_early_init_f (void) {
	volatile immap_t *im = (immap_t *)CONFIG_SYS_IMMR;
	volatile cpm8xx_t *cp = &(im->im_cpm);
	volatile iop8xx_t *iop = &(im->im_ioport);

	// Set PA6 to switch PAPAR to get CLK2 working
	iop->iop_papar |= 0x0200;

	// Set SCC4 to use BRG4 as clock source for Rx and Tx
	cp->cp_sicr = 0x1B000000;

#if defined CONFIG_USE_CLK2
	// Set BRG4 to use CLK2 and enable it
	cp->cp_brgc4 = CPM_BRG_EN | CPM_BRG_EXTC_CLK2;
#endif

	return 0;
}
**********************************************************************************

Maybe there's a better place to do this than board_early_init_f, but
it worked for me, and defining/undefining the CONFIG_USE_CLK2 flag
allows me to easily switch between BRGCLK and CLK2 as input clock to
my BRG1 and BRG4 if I ever decide to do so.

Hope somebody finds this useful.
Mikhail Zaturenskiy