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From:   "H. Nikolaus Schaller" <hns@goldelico.com>
To:     =?UTF-8?q?Marek=20Beh=C3=BAn?= <kabel@kernel.org>,
        Pavel Machek <pavel@ucw.cz>, Lee Jones <lee@kernel.org>
Cc:     linux-leds@vger.kernel.org, linux-kernel@vger.kernel.org,
        letux-kernel@openphoenux.org,
        "H. Nikolaus Schaller" <hns@goldelico.com>,
        NeilBrown <neilb@suse.de>,
        Linus Walleij <linus.walleij@linaro.org>
Subject: [PATCH] leds: tca6507: fix error handling of using fwnode_property_read_string
Date:   Sun,  2 Apr 2023 13:12:59 +0200
Message-Id: <cbae7617db83113de726fcc423a805ebaa1bfca6.1680433978.git.hns@goldelico.com>
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Precedence: bulk

Commit 96f524105b9c ("leds: tca6507: use fwnode API instead of OF")

changed to fwnode API but did not take into account that a missing property
"linux,default-trigger" now seems to return an error and as a side effect
sets value to -1. This seems to be different from of_get_property() which
always returned NULL in any case of error.

Neglecting this side-effect leads to

[   11.201965] Unable to handle kernel paging request at virtual address ffffffff when read

in the strcmp() of led_trigger_set_default() if there is no led-trigger
defined in the DTS.

I don't know if this was recently introduced somewhere in the fwnode lib
or if the effect was missed in initial testing. Anyways it seems to be a
bug to ignore the error return value of an optional value here in the
driver.

Fixes: 96f524105b9c ("leds: tca6507: use fwnode API instead of OF")
Cc: Marek Behún <kabel@kernel.org>
Cc: NeilBrown <neilb@suse.de>
Cc: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: H. Nikolaus Schaller <hns@goldelico.com>
---
 drivers/leds/leds-tca6507.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/leds/leds-tca6507.c b/drivers/leds/leds-tca6507.c
index 07dd12686a696..634cabd5bb796 100644
--- a/drivers/leds/leds-tca6507.c
+++ b/drivers/leds/leds-tca6507.c
@@ -691,8 +691,9 @@ tca6507_led_dt_init(struct device *dev)
 		if (fwnode_property_read_string(child, "label", &led.name))
 			led.name = fwnode_get_name(child);
 
-		fwnode_property_read_string(child, "linux,default-trigger",
-					    &led.default_trigger);
+		if (fwnode_property_read_string(child, "linux,default-trigger",
+						&led.default_trigger))
+			led.default_trigger = NULL;
 
 		led.flags = 0;
 		if (fwnode_device_is_compatible(child, "gpio"))
-- 
2.38.1