On Mon 17 May 04:13 CDT 2021, Andy Shevchenko wrote:

On Sun, May 16, 2021 at 6:47 AM Bjorn Andersson
[off-list ref] wrote:

quoted

In typec_mux_match() "nval" is assigned the number of elements in the
"svid" fwnode property, then the variable is used to store the success
of the read and finally attempts to loop between 0 and "success" - i.e.
not at all - and the code returns indicating that no match was found.

Fix this by using a separate variable to track the success of the read,
to allow the loop to get a change to find a match.

Fixes: 96a6d031ca99 ("usb: typec: mux: Find the muxes by also matching against the device node")
Signed-off-by: Bjorn Andersson <redacted>
---
 drivers/usb/typec/mux.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/usb/typec/mux.c b/drivers/usb/typec/mux.c
index 9da22ae3006c..8514bec7e1b8 100644
--- a/drivers/usb/typec/mux.c
+++ b/drivers/usb/typec/mux.c

@@ -191,6 +191,7 @@ static void *typec_mux_match(struct fwnode_handle *fwnode, const char *id,
        bool match;
        int nval;
        u16 *val;
+       int ret;
        int i;

        /*

@@ -218,10 +219,10 @@ static void *typec_mux_match(struct fwnode_handle *fwnode, const char *id,
        if (!val)
                return ERR_PTR(-ENOMEM);

-       nval = fwnode_property_read_u16_array(fwnode, "svid", val, nval);
-       if (nval < 0) {
+       ret = fwnode_property_read_u16_array(fwnode, "svid", val, nval);
+       if (ret < 0) {
                kfree(val);
-               return ERR_PTR(nval);
+               return ERR_PTR(ret);
        }

This changes the behaviour of the original code, i.e. nval can be
still positive but less than we got from previous call. Some fwnode
backends in some cases potentially can _successfully_ read less than
asked.

Perhaps

  nval = ret;

or drop the patch.

Per the kerneldoc of fwnode_property_read_u16_array:

 * Return: number of values if @val was %NULL,
 *         %0 if the property was found (success),

@val is not NULL, as we just checked for that, so the function will
always return 0 on success.

I don't see anything indicating that the number of elements can be
different from what fwnode_property_count_u16() returned.

Regards,
Bjorn

quoted

        for (i = 0; i < nval; i++) {

-- 
With Best Regards,
Andy Shevchenko