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Date: Fri, 06 Jul 2001 14:26:02 -0400
From: Chris Friesen <cfriesen@nortelnetworks.com>
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To: linux-kernel@vger.kernel.org
Cc: becker@scyld.com, root@chaos.analogic.com
Subject: why this 1ms delay in mdio_read?  (cont'd from "are ioctl calls supposed 
 to take this long?")
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The beginning of mdio_read() in tulip.c goes like this:

static int mdio_read(struct device *dev, int phy_id, int location)
{
	struct tulip_private *tp = (struct tulip_private *)dev->priv;
	int i;
	int read_cmd = (0xf6 << 10) | (phy_id << 5) | location;
	int retval = 0;
	long ioaddr = dev->base_addr;
	long mdio_addr = ioaddr + CSR9;

	if (tp->chip_id == LC82C168) {
		int i = 1000;
		outl(0x60020000 + (phy_id<<23) + (location<<18), ioaddr + 0xA0);
		inl(ioaddr + 0xA0);
		inl(ioaddr + 0xA0);
		while (--i > 0)
			if ( ! ((retval = inl(ioaddr + 0xA0)) & 0x80000000))
				return retval & 0xffff;
		return 0xffff;
	}

	if (tp->chip_id == COMET) {
		if (phy_id == 1) {
			if (location < 7)
				return inl(ioaddr + 0xB4 + (location<<2));
			else if (location == 17)
				return inl(ioaddr + 0xD0);
			else if (location >= 29 && location <= 31)
				return inl(ioaddr + 0xD4 + ((location-29)<<2));
		}
		return 0xffff;
	}

	mdelay(1); /* One ms delay... */

	...rest of code...


The chip I'm using is the DEC 21143, which means that we skip over the two
conditional blocks, so the first thing that happens when we call this is to
wait around doing nothing for a millisecond.  Is there some subtle reason why we
would want to wait around for a millisecond before doing anything?

Thanks for your help,

Chris



-- 
Chris Friesen                    | MailStop: 043/33/F10  
Nortel Networks                  | work: (613) 765-0557
3500 Carling Avenue              | fax:  (613) 765-2986
Nepean, ON K2H 8E9 Canada        | email: cfriesen@nortelnetworks.com
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