Re: [PATCH v2 2/2] gpiolib: check the 'ngpios' property in core gpiolib code

On Thu, Nov 18, 2021 at 09:12:59PM +0100, Bartosz Golaszewski wrote:

On Thu, Nov 18, 2021 at 6:06 PM Andy Shevchenko
[off-list ref] wrote:

quoted

On Thu, Nov 18, 2021 at 02:23:17PM +0100, Bartosz Golaszewski wrote:

quoted

Several drivers read the 'ngpios' device property on their own, but
since it's defined as a standard GPIO property in the device tree bindings
anyway, it's a good candidate for generalization. If the driver didn't
set its gc->ngpio, try to read the 'ngpios' property from the GPIO
device's firmware node before bailing out.

...

quoted

      if (gc->ngpio == 0) {
-             chip_err(gc, "tried to insert a GPIO chip with zero lines\n");
-             ret = -EINVAL;
-             goto err_free_descs;
+             ret = device_property_read_u32(&gdev->dev, "ngpios", &ngpios);
+             if (ret) {
+                     chip_err(gc, "tried to insert a GPIO chip with zero lines\n");
+                     ret = -EINVAL;
+                     goto err_free_descs;
+             }
+
+             gc->ngpio = ngpios;
      }

This should be

        if (gc->ngpio == 0) {
                ret = device_property_read_u32(&gdev->dev, "ngpios", &ngpios);
                if (ret)
                        return ret;

But device_property_read_u32() returning -ENODATA means there's no
such property, which should actually be converted to -EINVAL as the
caller wanting to create the chip provided invalid configuration - in
this case: a chip with 0 lines. In case of the non-array variant of
read_u32 that's also the only error that can be returned so this bit
looks right to me.

So, what is so special about -EINVAL? Why -ENODATA is not good enough which
will exactly explain to the caller what's going on, no?

quoted

                gc->ngpio = ngpios;
        }

        if (gc->ngpio == 0) {
                chip_err(gc, "tried to insert a GPIO chip with zero lines\n");
                ret = -EINVAL;
                goto err_free_descs;

When the caller intended to create a chip with 0 GPIOs they will get an error
as you wish with an error message.

quoted

        }

-- 
With Best Regards,
Andy Shevchenko