[src/trunk]: src/sys/dev/i2c Don't read from the chip when matching, fail the...

[jdc <jdc%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/921cde0b2a79
branches:  trunk
changeset: 957646:921cde0b2a79
user:      jdc <jdc%NetBSD.org@localhost>
date:      Sun Dec 06 10:09:36 2020 +0000

description:
Don't read from the chip when matching, fail the attach instead (requested
by jmcneill).  Reverts previous.

diffstat:

 sys/dev/i2c/pcf8574.c |  25 +++++++++----------------
 1 files changed, 9 insertions(+), 16 deletions(-)

diffs (55 lines):

diff -r c1f4ee0bfb17 -r 921cde0b2a79 sys/dev/i2c/pcf8574.c
--- a/sys/dev/i2c/pcf8574.c     Sun Dec 06 10:06:15 2020 +0000
+++ b/sys/dev/i2c/pcf8574.c     Sun Dec 06 10:09:36 2020 +0000
@@ -1,4 +1,4 @@
-/* $NetBSD: pcf8574.c,v 1.4 2020/12/05 15:02:29 jdc Exp $ */
+/* $NetBSD: pcf8574.c,v 1.5 2020/12/06 10:09:36 jdc Exp $ */
 
 /*-
  * Copyright (c) 2020 The NetBSD Foundation, Inc.
@@ -35,7 +35,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: pcf8574.c,v 1.4 2020/12/05 15:02:29 jdc Exp $");
+__KERNEL_RCSID(0, "$NetBSD: pcf8574.c,v 1.5 2020/12/06 10:09:36 jdc Exp $");
 
 #include <sys/param.h>
 #include <sys/systm.h>
@@ -108,21 +108,10 @@
 pcf8574_match(device_t parent, cfdata_t cf, void *aux)
 {
        struct i2c_attach_args *ia = aux;
-       struct pcf8574_softc sc;
        int match_result;
 
-       if (!iic_use_direct_match(ia, cf, compat_data, &match_result))
-               return 0;
-
-       /* Try a read so that we don't match on optional components */
-       if (match_result) {
-               sc.sc_tag = ia->ia_tag;
-               sc.sc_addr = ia->ia_addr;
-               if (pcf8574_read(&sc, &sc.sc_state))
-                       return 0;
-               else
-                       return match_result;
-       }
+       if (iic_use_direct_match(ia, cf, compat_data, &match_result))
+               return match_result;
 
        /* We don't support indirect matches */
        return 0;
@@ -153,7 +142,11 @@
         */
        sc->sc_mask = 0xff;
 
-       pcf8574_read(sc, &sc->sc_state);
+       /* Try a read, and fail if this component isn't present */
+       if (pcf8574_read(sc, &sc->sc_state)) {
+               aprint_normal(": read failed\n");
+               return;
+       }
 
 #ifdef PCF8574_DEBUG
        aprint_normal(": GPIO: state = 0x%02x\n", sc->sc_state);