Re: [PATCH] usb: typec: mux: Fix typec_switch_match()

[Heikki Krogerus <heikki.krogerus@linux.intel.com>]

On Mon, Aug 17, 2026 at 08:22:39PM +0200, Marek Vasut wrote:
> The fwnode_typec_switch_get() sporadically returns NULL instead of an
> -EPROBE_DEFER for orientation-switch described in DT. This makes it
> impossible to discern whether the DT does describe an orientation-switch
> which did not probe yet, or whether the DT does not describe the switch.
> This happens with gpio-sbu-mux connected to an I2C GPIO expander.
> 
> The class_find_device() on typec_switch_match() may return NULL in case
> the mux did not probe just yet early on boot. The sw_devs[] array can be
> empty on boot as well. If these two conditions occur, then the conditional
> if (to_typec_switch_dev(dev) == sw_devs[i]) evaluates to true and the match
> function returns NULL, which propagates to fwnode_typec_switch_get() which
> makes it look as if the orientation-switch was not described in DT.
> 
> This is incorrect, because the mux driver will probe a bit later on, but
> at that point, the caller of fwnode_typec_switch_get() already got the
> NULL return value. The NULL return value also does not trigger IS_ERR(),
> therefore the caller driver interprets this as if the orientation-switch
> is not described in DT, and does not return -EPROBE_DEFER to try again,
> even if it should.
> 
> Fix this by checking the class_find_device() return value, and return
> -EPROBE_DEFER if it is NULL right away. If the return value is not NULL,
> perform the deduplication test, and if that test passes, consider the
> return value to be already non-NULL.
> 
> Fixes: a53b4f9c51a9 ("usb: typec: mux: avoid duplicated orientation switches")
> Cc: stable@vger.kernel.org
> Signed-off-by: Marek Vasut <marex@nabladev.com>

Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>

> ---
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: Heikki Krogerus <heikki.krogerus@linux.intel.com>
> Cc: Jens Glathe <jens.glathe@oldschoolsolutions.biz>
> Cc: Sebastian Reichel <sebastian.reichel@collabora.com>
> Cc: kernel@dh-electronics.com
> Cc: linux-kernel@vger.kernel.org
> Cc: linux-usb@vger.kernel.org
> ---
> NOTE: A similar change was reverted in
>       f576c75f95a5 ("Revert "usb: typec: mux: avoid duplicated mux switches"")
>       Maybe the orientation switch commit also needs a revert ?
>       Or the mux switch revert can be undone and fixed using this NULL check ?
> ---
>  drivers/usb/typec/mux.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/typec/mux.c b/drivers/usb/typec/mux.c
> index 9b908c46bd7df..2bc7e8edb3cbd 100644
> --- a/drivers/usb/typec/mux.c
> +++ b/drivers/usb/typec/mux.c
> @@ -56,17 +56,19 @@ static void *typec_switch_match(const struct fwnode_handle *fwnode,
>  	 * function "defers probe" for now.
>  	 */
>  	dev = class_find_device(&typec_mux_class, NULL, fwnode,
>  				switch_fwnode_match);
> +	if (!dev)
> +		return ERR_PTR(-EPROBE_DEFER);
>  
>  	/* Skip duplicates */
>  	for (i = 0; i < TYPEC_MUX_MAX_DEVS; i++)
>  		if (to_typec_switch_dev(dev) == sw_devs[i]) {
>  			put_device(dev);
>  			return NULL;
>  		}
>  
> -	return dev ? to_typec_switch_dev(dev) : ERR_PTR(-EPROBE_DEFER);
> +	return to_typec_switch_dev(dev);
>  }
>  
>  /**
>   * fwnode_typec_switch_get - Find USB Type-C orientation switch
> -- 
> 2.53.0

-- 
heikki