[RFC v3 09/13] ARM: sunxi: Add support for Allwinner SUNXi SoCs sata to ahci_platform

[Russell King - ARM Linux]

On Sun, Jan 19, 2014 at 12:48:51AM +0100, Hans de Goede wrote:
> +	timeout = 0x100000;
> +	do {
> +		reg_val = sunxi_getbits(reg_base + AHCI_PHYCS0R, 0x7, 28);
> +	} while (--timeout && (reg_val != 0x2));
> +	if (!timeout) {
> +		dev_err(dev, "PHY power up failed.\n");
> +		return -EIO;
> +	}

This is not a good way to detect failure - there's several things wrong
here.

First, how long does sunxi_getbits() take?  What does that depend on?
Therefore, how long does it take to time out?

Secondly, what if the success condition becomes true at the same time that
a timeout occurs?

So:

	timeout = some_us_value;
	do {
		reg_val = sunxi_getbits(reg_base + AHCI_PHYCS0R, 0x7, 28);
		if (reg_val == 2)
			break;

		timeout--;
		if (timeout == 0) {
			dev_err(dev, "PHY power up failed.\n");
			return -EIO;
		}

		udelay(1);
	} while (1);

is far more predictable.  Same goes for the other loop in this function.

-- 
FTTC broadband for 0.8mile line: 5.8Mbps down 500kbps up.  Estimation
in database were 13.1 to 19Mbit for a good line, about 7.5+ for a bad.
Estimate before purchase was "up to 13.2Mbit".