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

[Marek Vasut <marex@nabladev.com>]

On 8/18/26 6:24 PM, Sebastian Reichel wrote:

Hello Sebastian,

> 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>
>> ---
>>
>> 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 ?
>> ---
> 
> This revert negatively affects Rockchip once my USB-C rework for
> USB-DP lands and I undid it locally. I've just not yet found the
> time to investigate why it regresses the X1E platform to reintroduce
> the feature. Maybe you found the root cause and fix already, but
> investigating with my T14s Gen6 Snapdragon is on my TODO list.
> 
> FWIW this patch is
> 
> Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Could you revert f576c75f95a5 ("Revert "usb: typec: mux: avoid 
duplicated mux switches"") and apply the following patch (equivalent to 
this patch, applies to mux instead of switch) and see if that fixes the 
T14s for you too then ? If yes, than, I think this might be the proper 
fix rather than the revert:

diff --git a/drivers/usb/typec/mux.c b/drivers/usb/typec/mux.c
index 4a4297f15aad3..afa6fc1813978 100644
--- a/drivers/usb/typec/mux.c
+++ b/drivers/usb/typec/mux.c
@@ -294,6 +294,8 @@ static void *typec_mux_match(const struct 
fwnode_handle *fwnode,

         dev = class_find_device(&typec_mux_class, NULL, fwnode,
                                 mux_fwnode_match);
+       if (!dev)
+               return ERR_PTR(-EPROBE_DEFER);

         /* Skip duplicates */
         for (i = 0; i < TYPEC_MUX_MAX_DEVS; i++)
@@ -303,7 +305,7 @@ static void *typec_mux_match(const struct 
fwnode_handle *fwnode,
                 }


-       return dev ? to_typec_mux_dev(dev) : ERR_PTR(-EPROBE_DEFER);
+       return to_typec_mux_dev(dev);
  }

  /**