linux-kernel - Re: [PATCH] leds: tca6507: fix error handling of using fwnode_property_read

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Date:   Mon, 3 Apr 2023 11:09:14 +0200
From:   Marek Behún <kabel@...nel.org>
To:     "H. Nikolaus Schaller" <hns@...delico.com>
Cc:     Pavel Machek <pavel@....cz>, Lee Jones <lee@...nel.org>,
        linux-leds@...r.kernel.org, linux-kernel@...r.kernel.org,
        letux-kernel@...nphoenux.org, NeilBrown <neilb@...e.de>,
        Linus Walleij <linus.walleij@...aro.org>
Subject: Re: [PATCH] leds: tca6507: fix error handling of using
 fwnode_property_read_string

On Sun,  2 Apr 2023 13:12:59 +0200
"H. Nikolaus Schaller" <hns@...delico.com> wrote:

> 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@...nel.org>
> Cc: NeilBrown <neilb@...e.de>
> Cc: Linus Walleij <linus.walleij@...aro.org>
> Signed-off-by: H. Nikolaus Schaller <hns@...delico.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"))

Reviewed-by: Marek Behún <kabel@...nel.org>