[Linux-parport] [PATCH] IEEE1284 Device ID read fixes

[Tim Waugh]

On Mon, Jan 10, 2005 at 08:33:35PM +0200, Marko Kohtala wrote:

> +	/* Some devices don't truly implement Device ID, but just
> +	   return constant nibble forever. This catches also those
> +	   cases. */
> +	if (idlen <= 2 || idlen > 0xFFF) {
> +		printk (KERN_DEBUG "%s: reported broken Device ID length of 
> %#zX bytes\n",
> +			port->name, idlen-2);
> +		return -EIO;
> +	}

Some manufacturers think that the first two bytes are little-endian,
so that last test will miss IDs from them altogether.  Sorry, I don't
remember which.

> +	/* Avoid reading past given ID length just in case some
> +	 * devices do not properly implement the end of data in Device
> +	 * ID nibble mode. */
> +	retval = parport_read (port, buffer+len,
> +			       min(count-len-1,idlen-2));

For some reason I had in my mind that you need to read to the end of
the data in order to make sure the device will start from the
beginning again next time.  Perhaps that's wrong.

Tim.
*/
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