Add iic_is_compatible() for matching I2C devices

When using device trees, the ia_name field of struct i2c_attach_args
points to the first string of the device node's "compatible" array.
However, in many cases it would be preferable to use the last, most
general "compatible" entry as a device matching criterion.

Enable more flexible device matching by permitting ia_name to point to
the raw "compatible" data which is a concatenation of NUL-terminated
strings. I2C bus code will supply the data and set ia_name and
ia_namelen. I2C device drivers will use iic_is_compatible() to check
matches. This method is also backwards compatible with the old, direct
use of ia_name.

Prompted by a related patch from kettenis@.

OK kettenis@

2 files changed, 27 insertions, 2 deletions

diff --git a/sys/dev/i2c/i2c.c b/sys/dev/i2c/i2c.c
index 4b44892cf3c..48e0ec96a76 100644
--- a/sys/dev/i2c/i2c.c
+++ b/sys/dev/i2c/i2c.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: i2c.c,v 1.17 2021/10/26 16:29:49 deraadt Exp $	*/
+/*	$OpenBSD: i2c.c,v 1.18 2022/02/09 07:58:24 visa Exp $	*/
 /*	$NetBSD: i2c.c,v 1.1 2003/09/30 00:35:31 thorpej Exp $	*/
 
 /*
@@ -143,3 +143,26 @@ iic_attach(struct device *parent, struct device *self, void *aux)
 	else
 		iic_scan(self, aux);
 }
+
+int
+iic_is_compatible(const struct i2c_attach_args *ia, const char *name)
+{
+	const char *end, *entry;
+
+	if (ia->ia_namelen > 0) {
+		/* ia_name points to a concatenation of strings. */
+		entry = ia->ia_name;
+		end = entry + ia->ia_namelen;
+		while (entry < end) {
+			if (strcmp(entry, name) == 0)
+				return (1);
+			entry += strlen(entry) + 1;
+		}
+	} else {
+		/* ia_name points to a string. */
+		if (strcmp(ia->ia_name, name) == 0)
+			return (1);
+	}
+
+	return (0);
+}
diff --git a/sys/dev/i2c/i2cvar.h b/sys/dev/i2c/i2cvar.h
index aaba3294055..72469227e8b 100644
--- a/sys/dev/i2c/i2cvar.h
+++ b/sys/dev/i2c/i2cvar.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: i2cvar.h,v 1.17 2019/07/22 14:37:06 jcs Exp $	*/
+/*	$OpenBSD: i2cvar.h,v 1.18 2022/02/09 07:58:24 visa Exp $	*/
 /*	$NetBSD: i2cvar.h,v 1.1 2003/09/30 00:35:31 thorpej Exp $	*/
 
 /*
@@ -111,6 +111,7 @@ struct i2c_attach_args {
 	i2c_addr_t	ia_addr;	/* address of device */
 	int		ia_size;	/* size (for EEPROMs) */
 	char		*ia_name;	/* chip name */
+	size_t		ia_namelen;	/* length of name concatenation */
 	void		*ia_cookie;	/* pass extra info from bus to dev */
 	void		*ia_intr;	/* interrupt info */
 	int		ia_poll;	/* to force polling */
@@ -164,5 +165,6 @@ int	iic_smbus_receive_byte(i2c_tag_t, i2c_addr_t, uint8_t *, int);
 	(*(ic)->ic_intr_string)((ic)->ic_cookie, (ih))
 
 void	iic_ignore_addr(u_int8_t addr);
+int	iic_is_compatible(const struct i2c_attach_args *, const char *);
 
 #endif /* _DEV_I2C_I2CVAR_H_ */