On Mon, Feb 01, 2021 at 01:53:16PM +0100, Bartosz Golaszewski wrote:

On Mon, Feb 1, 2021 at 1:49 PM Andy Shevchenko
[off-list ref] wrote:

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On Mon, Feb 01, 2021 at 11:59:31AM +0100, Bartosz Golaszewski wrote:

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On Mon, Feb 1, 2021 at 11:28 AM Andy Shevchenko
[off-list ref] wrote:

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On Sat, Jan 30, 2021 at 09:37:55PM +0100, Bartosz Golaszewski wrote:

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On Fri, Jan 29, 2021 at 4:57 PM Andy Shevchenko
[off-list ref] wrote:

quoted

On Fri, Jan 29, 2021 at 02:46:24PM +0100, Bartosz Golaszewski wrote:

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+struct gpio_sim_chip_config {
+     struct config_item item;
+
+     /*
+      * If pdev is NULL, the item is 'pending' (waiting for configuration).
+      * Once the pointer is assigned, the device has been created and the
+      * item is 'live'.
+      */
+     struct platform_device *pdev;

Are you sure

        struct device *dev;

is not sufficient?

It may be but I really prefer those simulated devices to be on the platform bus.

My point here is that there is no need to keep specific bus devices type,
because you may easily derive it from the struct device pointer. Basically if
you are almost using struct device in your code (seems to me the case), you
won't need to carry bus specific one and dereference it each time.

But don't we need a bus to even register a device? I haven't checked
in a long time but IIRC it's mandatory.

Let me give you a different argument - the platform device offers a
very simple API for registering devices with properties being
duplicated behind the scenes etc. It seems to me that registering a
bare struct device * would take more boiler-plate code for not much
gain.

Yes, I'm not objecting the platform bus choice. I'm objecting the keeping of
the pointer to the bus specific structure.

There are helpers like to_platform_device() which make the bus specific
pointers go away from the structures and easier code when you use exactly
pointer to struct device rather than bus specific one.

Ok I get it. We almost never dereference it though. We do it in probe,
but there's no way around it. In sysfs callbacks we already get a
pointer to struct device. And when unregistering the platform device,
we need to pass it as struct platform_device anyway. I don't see any
gain from that and would prefer to keep it as is.

It's purely trade off, if you have more *dev in use, better to use *dev, if
*pdev, then use it, although my practice shows that in most cases keeping bus
specific pointer is an overkill.

-- 
With Best Regards,
Andy Shevchenko