Re: [PATCH RFC v3 3/3] pinctrl: add pinctrl gpio binding support

On 05/23/2012 07:22 AM, Dong Aisheng wrote:

From: Dong Aisheng <redacted>

This patch implements a standard common binding for pinctrl gpio ranges.
Each SoC can add gpio ranges through device tree by adding a gpio-maps property
under their pinctrl devices node with the format:
<&gpio $gpio_offset $pin_offset $npin>.

Then the pinctrl driver can call pinctrl_dt_add_gpio_ranges(pctldev, node)
to parse and register the gpio ranges from device tree.

Signed-off-by: Dong Aisheng <redacted>

This is mostly good. Just a few comments:

+gpio-maps: 4 integers array, each entry in the array represents a gpio
+range with the format: <&gpio $gpio_offset $pin_offset $count>
+- gpio: phandle pointing at gpio device node
+- gpio_offset: integer, the local offset of $gpio
+- pin_offset: integer, the pin offset or pin id
+- npins: integer, the gpio ranges starting from pin_offset

This uses a single cell to represent a GPIO ID within a GPIO controller.
The standard GPIO bindings use #gpio-cells, where that's a property in
the GPIO controller's node. I wonder if we shouldn't do the same here,
and call into the GPIO driver to parse #gpio-cells and give back the
Linux GPIO ID, just like of_get_named_gpio_flags() does. This would also
make this code able to cope with the GPIO of_xlate function returning a
different GPIO chip, which Grant put in place for banked GPIO controllers.

+int pinctrl_dt_add_gpio_ranges(struct pinctrl_dev *pctldev,

The locking I was talking about before is between the following line:

+		ranges[i].gc = of_node_to_gpiochip(np_gpio);

and this code:

+		ranges[i].name = dev_name(pctldev->dev);
+		ranges[i].base = ranges[i].gc->base + gpio_offset;
+		ranges[i].pin_base = pin_offset;
+		ranges[i].npins = npins;

If of_node_to_gpiochip() doesn't mark the GPIO chip as "in use", then
the module that provides that device could be unloaded between the two
blocks of code above.

Re: your locking comments in your other email: ranges[i].gc doesn't
appear to be used anywhere else in pinctrl, so I think it's OK not to
lock the GPIO chip for any more time than between the above two blocks
of code.

Finally, just a minor nit:

+		ranges[i].gc = of_node_to_gpiochip(np_gpio);
+		if (!ranges[i].gc) {
+			dev_err(pctldev->dev,
+				"can not find gpio chip of node(%s)\n",
+				np_gpio->name);
+			of_node_put(np_gpio);
+			return -EPROBE_DEFER;
+		}
+
+		of_node_put(np_gpio);

could be slightly simpler:

+		ranges[i].gc = of_node_to_gpiochip(np_gpio);
+		of_node_put(np_gpio); <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
+		if (!ranges[i].gc) {
+			dev_err(pctldev->dev,
+				"can not find gpio chip of node(%s)\n",
+				np_gpio->name);
+			return -EPROBE_DEFER;
+		}