On Thu, Dec 05, 2024 at 12:57:38PM -0800, Dmitry Torokhov wrote:
> On Wed, Dec 04, 2024 at 03:16:34AM +0200, Andy Shevchenko wrote:
> > On Tue, Dec 03, 2024 at 02:45:49PM -0800, Dmitry Torokhov wrote:
> > > On Tue, Dec 03, 2024 at 03:27:31PM +0200, Andy Shevchenko wrote:
> > > > On Mon, Dec 02, 2024 at 09:49:06PM -0800, Dmitry Torokhov wrote:
> > > > > On Sat, Nov 30, 2024 at 11:44:04PM +0200, Andy Shevchenko wrote:
> > > > > > On Fri, Nov 29, 2024 at 11:16:54PM -0800, Dmitry Torokhov wrote:
> > > > > > > On Fri, Nov 29, 2024 at 04:50:15PM +0200, Andy Shevchenko wrote:
> > > > > > > > On Thu, Nov 28, 2024 at 03:04:50PM -0800, Dmitry Torokhov wrote:
> > > > > > > > > On Thu, Nov 28, 2024 at 03:13:16PM +0200, Andy Shevchenko wrote:
> > > > > > > > > > On Wed, Nov 27, 2024 at 09:39:34PM -0800, Dmitry Torokhov wrote:
...
> > > > > > > > > > > @@ struct fwnode_handle *device_get_next_child_node(const struct device *dev,
> > > > > > > > > > > const struct fwnode_handle *fwnode = dev_fwnode(dev);
> > > > > > > > > > > struct fwnode_handle *next;
> > > > > > > > > >
> > > > > > > > > > > - if (IS_ERR_OR_NULL(fwnode))
> > > > > > > > > > > + if (IS_ERR_OR_NULL(fwnode)) {
> > > > > > > > > > > + fwnode_handle_put(child);
> > > > > > > > > > > return NULL;
> > > > > > > > > > > + }
> > > > > > > > > >
> > > > > > > > > > > /* Try to find a child in primary fwnode */
> > > > > > > > > > > next = fwnode_get_next_child_node(fwnode, child);
> > > > > > > > > >
> > > > > > > > > > So, why not just moving the original check (w/o dropping the reference) here?
> > > > > > > > > > Wouldn't it have the same effect w/o explicit call to the fwnode_handle_put()?
> > > > > > > > >
> > > > > > > > > Because if you rely on check in fwnode_get_next_child_node() you would
> > > > > > > > > not know if it returned NULL because there are no more children or
> > > > > > > > > because the node is invalid. In the latter case you can't dereference
> > > > > > > > > fwnode->secondary.
> > > > > > > >
> > > > > > > > Yes, so, how does it contradict my proposal?
> > > > > > >
> > > > > > > I guess I misunderstood your proposal then. Could you please explain it
> > > > > > > in more detail?
> > > > > >
> > > > > >
> > > > > > Current code (in steps):
> > > > > > if (IS_ERR_OR_NULL()) check
> > > > > > trying primary
> > > > > > trying secondary if previous is NULL
> > > > > >
> > > > > >
> > > > > > My proposal
> > > > > >
> > > > > > trying primary
> > > > > > return if not NULL
> > > > > > if (IS_ERR_OR_NULL()) check in its current form (no put op)
> > > > > > trying secondary
> > > > > >
> > > > > > After your first patch IIUC this is possible as trying primary will put child uncoditionally.
> > > > >
> > > > > Ah, I see. No, I do not think this is a good idea: it will make the code
> > > > > harder to understand for a casual reader: "Why do we check node validity
> > > > > only after we used it for the first time?"
> > > >
> > > > Theare a re already a few API calls there that are hard to understand, I spent
> > > > some time on them to get it through and still got it wrong as this series
> > > > shows. So, I don't think we anyhow change this.
> > >
> > > The fact that some code is confusing does not mean that we should add
> > > more confusing code. We will not fix everything at once, but we can make
> > > things better bit by bit.
> > >
> > > Look, the check where it is now makes total sense, you added it there
> > > yourself! It checks that we are dealing with a valid node and returns
> > > early. The intent is very easy to understand and the only thing that is
> > > missing is that "put" operation to satisfy the documented behavior.
> > > Anything more just makes things more complex for no good reason.
> >
> > Right, that's why I think we need to go away from open coding the iteration
> > over the list of nodes (primary, secondary, etc).
> >
> > > > > For the code not in a hot path there is a lot of value in simplicity.
> > > >
> > > > If you really want to go to this rabbit hole, think how we can get rid of
> > > > repetitive checks of the secondary or more if any in the future nodes in the
> > > > list.
> > > >
> > > > So the basic idea is to have this all hidden (to some extent) behind the macro
> > > > or alike. In the code it would be something as
> > > >
> > > > for node in primary, secondary, ...
> > > > call the API
> > > > if (okay)
> > > > return result
> > > >
> > > > return error
> > > >
> > > > This will indeed help.
> > >
> > > I think this will indeed help if we ever going to have more than primary
> > > and secondary nodes. It is also tricky if you want to transition
> > > seamlessly between different types of nodes (i.e. you have ACPI primary
> > > with OF overlay secondary with swnode as tertiary etc). And you probably
> > > want to add support for references between different typesof nodes
> > > (i.e. swnode being able to reference OF device node for example).
> > >
> > > This kind of rework is however out of scope of what I have time to do at
> > > the moment.
> >
> > I am not asking you to invest into big rework, the idea is to try to fold the
> > iterations to a kind of loop. Is it feasible?
>
> We could potentially do something like below.
>
> BTW, do you know why fwnode_property_get_reference_args() returns
> -ENOENT for NULL or error fwnode instead of -EINVAL as the rest of them?
I think we need to ask author, but I believe it's due to the OF analogue.
(Haven't checked myself, though)
> And would you object to unifying this?
...
> +#define FWNODE_ITERATE(n, result, cont_val, op, ...) \
for_each_fwnode() or alike.
> +({ \
> + int __ret = -EINVAL; \
> + typeof(result) __r; \
> + \
> + for (const struct fwnode_handle *__node = n; \
> + !IS_ERR_OR_NULL(__node); \
> + __node = __node->secondary) { \
> + if (!__node->ops || !__node->ops->op) { \
> + __ret = -ENXIO; \
> + continue; \
> + } \
> + __r = __node->ops->op(__node, ## __VA_ARGS__); \
> + if (__r != cont_val) { \
> + result = __r; \
> + __ret = 0; \
> + break; \
> + } \
> + } \
> + __ret; \
With a bit of polishing this may be the way to go.
> +})
--
With Best Regards,
Andy Shevchenko
