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

On Thu, May 24, 2012 at 4:44 AM, Stephen Warren [off-list ref] wrote:

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

quoted

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:

quoted

+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.

I checked the code, the second cell only represents gpio flag in
of_gpio_simple_xlate which seems meaningless to pinctrl, so it looks
increase overhead to pinctrl gpio ranges map.
However, it seems i may have to agree that we need keep align with the
exist of gpio design to use the standard way to get gpio number via
of_xlate function rather than do it privately in pinctrl driver.

One disadvantage is that i can not reuse of_get_named_gpio_flags due
to different format
for gpio-maps, i may have to write a slightly different one as
of_get_named_gpio_flags
for gpio-maps.

quoted

diff --git a/drivers/pinctrl/devicetree.c b/drivers/pinctrl/devicetree.c

quoted

+int pinctrl_dt_add_gpio_ranges(struct pinctrl_dev *pctldev,

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

quoted

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

and this code:

quoted

+             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.

Correct.

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.

So i will add lock between them like:
ranges[i].gc = of_node_to_gpiochip(np_gpio);
if (!try_module_get(ranges[i].gc->owner))
    err...
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;
module_put(ranges[i].gc->owner)
If anything wrong please let me know.

Finally, just a minor nit:

quoted

+             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);

Because here still uese np_gpio,  Can i still use it after of_node_put?

+                       return -EPROBE_DEFER;
+               }

Regards
Dong Aisheng