Re: [PATCH v3 2/2] gpiolib: check the 'ngpios' property in core gpiolib code

[Bartosz Golaszewski <brgl@bgdev.pl>]

On Wed, Nov 24, 2021 at 3:47 PM Andy Shevchenko
<andriy.shevchenko@linux.intel.com> wrote:
>
> On Wed, Nov 24, 2021 at 01:28:50PM +0100, Bartosz Golaszewski wrote:
> > 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.
>
> > Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>
> > Suggested-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> > Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
> > ---
> > v1 -> v2:
> > - use device_property_read_u32() instead of fwnode_property_read_u32()
> > - reverse the error check logic
> >
> > v2 -> v3:
> > - don't shadow errors other than -ENODATA in device_property_read_u32()
> >
> >  drivers/gpio/gpiolib.c | 15 ++++++++++++---
> >  1 file changed, 12 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> > index ede8b8a7aa18..f79fd2551cf7 100644
> > --- a/drivers/gpio/gpiolib.c
> > +++ b/drivers/gpio/gpiolib.c
> > @@ -599,6 +599,7 @@ int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data,
> >       int base = gc->base;
> >       unsigned int i;
> >       int ret = 0;
> > +     u32 ngpios;
> >
> >       /*
> >        * First: allocate and populate the internal stat container, and
> > @@ -647,9 +648,17 @@ int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data,
> >       }
>
> >       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) {
> > +                     if (ret == -ENODATA) {
> > +                             chip_err(gc, "tried to insert a GPIO chip with zero lines\n");
> > +                             ret = -EINVAL;
> > +                     }
> > +
> > +                     goto err_free_descs;
> > +             }
>
> And if the property returns 0 in ngpios?
>
> What about the modified suggestion from previous version:
>
>         if (gc->ngpio == 0) {
>                 ret = device_property_read_u32(&gdev->dev, "ngpios", &ngpios);

The comment is a good idea but other than that - it's overcomplicating things.

>                 if (ret == -ENODATA)
>                         ngpios = 0;
>                 else if (ret)
>                         return ret;

You still need to goto err_free_descs here.

>
>                 gc->ngpio = ngpios;
>         }
>
>         if (gc->ngpio == 0) {

Why check that again? We already know the driver set it to 0, we
checked it a couple lines before. If we can't get the setting from the
properties then it won't be non 0 here right?

>                 chip_err(gc, "tried to insert a GPIO chip with zero lines\n");
>                 ret = -EINVAL;
>                 goto err_free_descs;
>         }
>
> ?
>
> > +             gc->ngpio = ngpios;
> >       }
> >
> >       if (gc->ngpio > FASTPATH_NGPIO)
> > --
> > 2.25.1
> >
>
> --
> With Best Regards,
> Andy Shevchenko
>
>

I suggest the following:

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index ede8b8a7aa18..08c1e8fc0dfa 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -599,6 +599,7 @@ int gpiochip_add_data_with_key(struct gpio_chip
*gc, void *data,
     int base = gc->base;
     unsigned int i;
     int ret = 0;
+    u32 ngpios;

     /*
      * First: allocate and populate the internal stat container, and
@@ -647,9 +648,23 @@ int gpiochip_add_data_with_key(struct gpio_chip
*gc, void *data,
     }

     if (gc->ngpio == 0) {
-        chip_err(gc, "tried to insert a GPIO chip with zero lines\n");
-        ret = -EINVAL;
-        goto err_free_descs;
+        /*
+         * If the driver didn't specify the number of GPIOs, try to
+         * get this value from the device properties as a fall-back.
+         */
+        ret = device_property_read_u32(&gdev->dev, "ngpios", &ngpios);
+        if (ret) {
+            /*
+             * -ENODATA means that there is no property found and
+             * we want to issue the error message to the user.
+             * Besides that, we want to return different error code
+             * to state that supplied value is not valid.
+             * */
+            if (ret == -ENODATA) {
+                chip_err(gc, "tried to insert a GPIO chip with zero lines\n");
+                ret = -EINVAL;
+            }
+
+            goto err_free_descs;
+        }
+
+        gc->ngpio = ngpios;
     }

     if (gc->ngpio > FASTPATH_NGPIO)