[U-Boot] [PATCH v3 1/4] mips: add base support for atheros ath79 based SOCs

[Marek Vasut <marex@denx.de>]

On Friday, December 25, 2015 at 12:38:39 PM, Wills Wang wrote:
> On 12/24/2015 11:12 PM, Marek Vasut wrote:
> > On Thursday, December 24, 2015 at 02:51:06 PM, Wills Wang wrote:
> > 
> > [...]
> > 
> >>>> +LEAF(lowlevel_init)
> >>>> +   /* These three WLAN_RESET will avoid original issue */
> >>>> +    li      t3, 0x03
> >>>> +1:
> >>>> +    li      t0, KSEG1ADDR(AR71XX_RESET_BASE)
> >>>> +    lw      t1, AR933X_RESET_REG_RESET_MODULE(t0)
> >>>> +    ori     t1, t1, 0x0800
> >>>> +    sw      t1, AR933X_RESET_REG_RESET_MODULE(t0)
> >>>> +    nop
> >>>> +    lw      t1, AR933X_RESET_REG_RESET_MODULE(t0)
> >>>> +    li      t2, 0xfffff7ff
> >>>> +    and     t1, t1, t2
> >>>> +    sw      t1, AR933X_RESET_REG_RESET_MODULE(t0)
> >>>> +    nop
> >>>> +    addi    t3, t3, -1
> >>>> +    bnez    t3, 1b
> >>>> +     nop
> >>> 
> >>> This should be also easy to rewrite into C , right ?
> >> 
> >> C runtime environment is not available.
> >> C stack is not ready before DDR has initialized.
> > 
> > Just point the stack into a locked cacheline or some onchip RAM and there
> > you have a C runtime. That should be pretty easy :)
> 
> How to lock cacheline?

You'd have to check the MIPS core manual, I don't know the details, sorry.

> My guess is that cache memory may be use to map SPI flash at 0x9f000000
> by ROM code.

The SPI flash is an IP block which just maps the SPI NOR into the address space,
it doesn't use the CPU cache at all.

Maybe you don't even need to lock cachelines though, the AR9331 should have some 
internal SRAM, so just use that for stack. Do you have a proper datasheet for 
the Atheros MIPS chips ? I have some 320 pages datasheet for AR9331.

> > [...]
> > 
> >>>> +phys_size_t initdram(int board_type)
> >>>> +{
> >>>> +	uint8_t *addr, *p;
> >>>> +	int i;
> >>>> +
> >>>> +	ddr_tap_init();
> >>>> +	addr = (uint8_t *)KSEG1;
> >>>> +	*addr = 0x77;
> >>>> +	for (i = 0, p = addr; p < (uint8_t *)KSEG2; i++) {
> >>>> +		p += 0x1000000;
> >>>> +		*p = i;
> >>>> +		if (*addr != 0x77)
> >>>> +			break;
> >>>> +	}
> >>> 
> >>> What is this and how does it work ?
> >> 
> >> Physical memory was mapped circularly for this chip.
> > 
> > Can you please expand on that ? I am not as deep in this chip as you are,
> > so please explain it to me in a bit more detail.

Well ... ?

> >>>> +	return (phys_size_t)(p - addr);
> >>>> +}
> > 
> > [...]
> > 
> >>>> +	if (reg) {
> >>>> +		val = RST_READ(reg);
> >>>> +		val |= AR71XX_RESET_FULL_CHIP;
> >>>> +		RST_WRITE(reg, val);
> >>> 
> >>> setbits_le32() please.
> >> 
> >> Macro setbits_le32() is not available for MIPS architecture.
> > 
> > You can always add them :)
> > 
> >> Other, I don't think there is better in being so explicit and using
> >> little-endian.
> > 
> > I believe your register accesses should have correct endianness exactly
> > beause mips can be both endian.
> 
> What is the advantage of using setbits_le32()?

You don't have these constant repeating patterns of:

var = read()
var |= BIT
write(var)

It makes things a bit less confusing.

Best regards,
Marek Vasut