RE: [ethtool PATCH v4 10/11] ethtool.c: add support for ETHTOOL_xLINKSETTINGS ioctls

quoted

+	/* ignore optional '0x' prefix */
+	if ((slen > 2) && (

Unnecessary ().

quoted

+		    (0 == memcmp(s, "0x", 2)
+		     || (0 == memcmp(s, "0X", 2))))) {

A-about-F comparisons.

memcmp() is a really poor tool for comparing strings.  You should use
strncasecmp() here.

Even that is overkill, why not just:
	if (s[0] == '0' && (s[1] == 'x' || s[1] == 'X'))

	David