Messages in this thread | | | Date | Mon, 21 Feb 2022 19:19:22 +0200 | From | Andy Shevchenko <> | Subject | Re: [PATCH v2 1/6] device property: Helper to match multiple connections |
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On Sun, Feb 20, 2022 at 08:55:10PM -0800, Bjorn Andersson wrote: > On Sun 20 Feb 03:16 PST 2022, Andy Shevchenko wrote: > > On Fri, Feb 18, 2022 at 11:00:45AM -0800, Bjorn Andersson wrote: > > > On Wed 09 Feb 04:30 PST 2022, Andy Shevchenko wrote: > > > > On Mon, Feb 07, 2022 at 07:19:39PM -0800, Bjorn Andersson wrote:
...
> > > > > +int fwnode_connection_find_matches(struct fwnode_handle *fwnode, > > > > > + const char *con_id, void *data, > > > > > + devcon_match_fn_t match, > > > > > + void **matches, unsigned int matches_len) > > > > > +{ > > > > > + unsigned int count; > > > > > + > > > > > + if (!fwnode || !match || !matches) > > > > > > > > !matches case may be still useful to get the count and allocate memory by > > > > caller. Please, consider this case. > > > > > > As discussed in previous version, and described in the commit message, > > > the returned value of "match" is a opaque pointer to something which > > > has to be passed back to the caller in order to be cleaned up. > > > > > > E.g. the typec mux code returns a pointer to a typec_mux/switch object > > > with a refcounted struct device within, or an ERR_PTR(). > > > > > > So unfortunately we can must gather the results into matches and pass it > > > back to the caller to take consume or clean up. > > > > It's fine. You have **matches, means pointer of an opaque pointer. > > What I'm talking about is memory allocation for and array of _pointers_. > > That's what caller very much aware of and can allocate on heap. So, please > > consider this case. > > I'm sorry, but I'm not sure what you're looking for. > > > I still interpret your comment as that it would be nice to be able to do > something like: > > count = fwnode_connection_find_matches(fwnode, "orientation-switch", > NULL, typec_switch_match, NULL, 0); > > based on the returned value the caller could allocate an array of > "count" pointers and then call the function again to actually fill out > the count elements.
Yes, that's what I want from the generic fwnode APIs. (Keyword: generic)
> The problem with this is that, typec_switch_match() does:
As you stated, the problem is in the typec_switch_match(). So, it's not related to the fwnode, but how you are using it.
> void *typec_switch_match(fwnode, id, data) { > struct device *dev = find_struct_device(fwnode, id); > if (!dev) > return NULL; > get_device(dev); > return container_of(dev, struct typec_switch, dev); > } > > So if we call the match function and if that finds a "dev" it will > return a struct typec_switch with a refcounted struct device within.
fwnode (as being an abstraction on top of the others) has no knowledge about this. And more important should not know that.
> We can see if that's NULL or not and will be able to return a "count", > but we have no way of releasing the reference acquired - we must return > the void pointer back to the client, so that it can release it.
The caller (if it wants to!) may create different callbacks for count and real matching, no?
> My claim is that this is not a problem, because this works fine with any > reasonable size of fwnode graphs we might run into - and the client will > in general have a sense of the worst case number of matches (in this > series its 3, as there's 3 types of lanes that can be switched/muxed > coming out of a USB connector).
-- With Best Regards, Andy Shevchenko
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