Re: [PATCH v3 02/15] Driver core: Unified device properties interface for platform firmware

Rafael J. Wysocki
2014-10-02T16:30:09Z

On Thursday, October 02, 2014 09:46:29 AM Arnd Bergmann wrote:
> On Thursday 02 October 2014 00:09:44 Rafael J. Wysocki wrote:
> > On Wednesday, October 01, 2014 09:47:40 AM Arnd Bergmann wrote:
> > > On Wednesday 01 October 2014 04:10:03 Rafael J. Wysocki wrote:
> > > I still have my reservations against the child accessors, and would
> > > like to hear what other people think. Passing a void pointer rather
> > > than struct fw_dev_node has both advantages and disadvantages, and
> > > I won't complain about either one if enough other people on the DT
> > > side would like to see the addition of the child functions.
> >
> > I actually would rather like to know if the people on the DT side have any
> > problems with the child functions.
>
> Sure, any kind of feedback would be helpful really.
>
> > Because, suppose that they wouldn't like those functions at all. What are we
> > supposed to do, then, honestly? Add the whole DT vs ACPI logic to the leds-gpio
> > and gpio_keys_polled drivers? But these drivers have no reason whatsoever
> > to include that. Zero.
> >
> > So suggestions welcome.
> >
> > [BTW, In principle we also could use something like
> >
> > typedef union dev_node {
> > struct acpi_device *acpi_node;
> > struct device_node *of_node;
> > } dev_node_t;
> >
> > instead of the (void *) for more type safety. It still is useful to pass the
> > parent pointer along with that, though.]
>
> Yes, I'm not worried about the implementation details.
>
> > > > Finally, device_for_each_child_node() is added for iterating over
> > > > the children of the device description object associated with a
> > > > given device.
> > > >
> > > > The interface covers both ACPI and Device Trees.
> > > >
> > > > This change set includes material from Mika Westerberg and Aaron Lu.
> > > >
> > >
> > > Regarding device_for_each_child_node(), the syntax is inconsistent
> > > with what we normally use, which can probably be changed. All of the
> > > DT for_each_* helpers are macros that are used like
> > >
> > > struct device *dev = ...;
> > > void *child; /* iterator */
> > >
> > > device_for_each_child_node(dev, child) {
> > > u32 something;
> > > device_child_property_read_u32(dev, child, "propname", &something);
> > >
> > > do_something(dev, something);
> > > }
> > >
> > > If we get a consensus on having the child interfaces, I'd rather see
> > > them done this way than with a callback pointer, for consistency
> > > reasons.
> >
> > That certainly is doable, although the resulting macro would generate a rather
> > large chunk of code each time it is used.
>
>
> #define device_for_each_child_node(dev, child) \
> for (child = device_get_next_child_node(dev, NULL), child, \
> child = device_get_next_child_node(dev, child))
>
> void *device_get_next_child_node(struct device *dev, void *child)
> {
> if (IS_ENABLED(CONFIG_OF) && dev->of_node)
> return of_get_next_child(dev->of_node, child);
> else if (IS_ENABLED(CONFIG_ACPI) && ...)
> return acpi_get_next_child(dev, child);
> return NULL;
> }
>
> Not any more code than what we have today for the DT-only case, and it's
> really just a function call in a loop.

OK, I see what you mean.

Now we have the if () on every iteration instead of just doing that once
upfront. Not a big deal I suppose, but slightly ugly to me.

--
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.