RE: [PATCH v3 1/1] device property: Allow error pointer to be passed to fwnode APIs

[Sa, Nuno]

> -----Original Message-----
> From: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
> Sent: Monday, March 7, 2022 9:30 PM
> To: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>; Rafael J.
> Wysocki <rafael.j.wysocki@xxxxxxxxx>; linux-acpi@xxxxxxxxxxxxxxx;
> linux-kernel@xxxxxxxxxxxxxxx
> Cc: Daniel Scally <djrscally@xxxxxxxxx>; Heikki Krogerus
> <heikki.krogerus@xxxxxxxxxxxxxxx>; Sakari Ailus
> <sakari.ailus@xxxxxxxxxxxxxxx>; Greg Kroah-Hartman
> <gregkh@xxxxxxxxxxxxxxxxxxx>; Rafael J. Wysocki
> <rafael@xxxxxxxxxx>; Len Brown <lenb@xxxxxxxxxx>; Sa, Nuno
> <Nuno.Sa@xxxxxxxxxx>
> Subject: [PATCH v3 1/1] device property: Allow error pointer to be
> passed to fwnode APIs
> 
> [External]
> 
> Some of the fwnode APIs might return an error pointer instead of
> NULL
> or valid fwnode handle. The result of such API call may be considered
> optional and hence the test for it is usually done in a form of
> 
> 	fwnode = fwnode_find_reference(...);
> 	if (IS_ERR(fwnode))
> 		...error handling...
> 
> Nevertheless the resulting fwnode may have bumped the reference
> count
> and hence caller of the above API is obliged to call
> fwnode_handle_put().
> Since fwnode may be not valid either as NULL or error pointer the
> check
> has to be performed there. This approach uglifies the code and adds
> a point of making a mistake, i.e. forgetting about error point case.
> 
> To prevent this, allow an error pointer to be passed to the fwnode
> APIs.
> 
> Fixes: 83b34afb6b79 ("device property: Introduce
> fwnode_find_reference()")
> Reported-by: Nuno Sá <nuno.sa@xxxxxxxxxx>
> Signed-off-by: Andy Shevchenko
> <andriy.shevchenko@xxxxxxxxxxxxxxx>
> Tested-by: Nuno Sá <nuno.sa@xxxxxxxxxx>
> ---
> 
> v3: dropped test of secondary fwnode (Nuno), added tag (Nuno),
> amended commit message
> v2: adjusted the entire fwnode API (Sakari)
> 
> Nuno, can you re-test this with the ltc2983 series to be sure it is still
> okay?

Still works!

>  drivers/base/property.c | 76 +++++++++++++++++++++++-------------
> -----
>  include/linux/fwnode.h  | 10 +++---
>  2 files changed, 48 insertions(+), 38 deletions(-)
> 
> diff --git a/drivers/base/property.c b/drivers/base/property.c
> index c0e94cce9c29..635a0e556a4f 100644
> --- a/drivers/base/property.c
> +++ b/drivers/base/property.c
> @@ -9,6 +9,7 @@
> 
>  #include <linux/acpi.h>
>  #include <linux/export.h>
> +#include <linux/fwnode.h>
>  #include <linux/kernel.h>
>  #include <linux/of.h>
>  #include <linux/of_address.h>
> @@ -47,12 +48,14 @@ bool fwnode_property_present(const struct
> fwnode_handle *fwnode,
>  {
>  	bool ret;
> 
> +	if (IS_ERR_OR_NULL(fwnode))
> +		return false;
> +
>  	ret = fwnode_call_bool_op(fwnode, property_present,
> propname);
> -	if (ret == false && !IS_ERR_OR_NULL(fwnode) &&
> -	    !IS_ERR_OR_NULL(fwnode->secondary))
> -		ret = fwnode_call_bool_op(fwnode->secondary,
> property_present,
> -					 propname);
> -	return ret;
> +	if (ret == true)
> +		return ret;
> +
> +	return fwnode_call_bool_op(fwnode->secondary,
> property_present, propname);
>  }
>  EXPORT_SYMBOL_GPL(fwnode_property_present);
> 
> @@ -232,15 +235,16 @@ static int
> fwnode_property_read_int_array(const struct fwnode_handle
> *fwnode,
>  {
>  	int ret;
> 
> +	if (IS_ERR_OR_NULL(fwnode))
> +		return -EINVAL;
> +
>  	ret = fwnode_call_int_op(fwnode, property_read_int_array,
> propname,
>  				 elem_size, val, nval);
> -	if (ret == -EINVAL && !IS_ERR_OR_NULL(fwnode) &&
> -	    !IS_ERR_OR_NULL(fwnode->secondary))
> -		ret = fwnode_call_int_op(
> -			fwnode->secondary, property_read_int_array,
> propname,
> -			elem_size, val, nval);
> +	if (ret != -EINVAL)
> +		return ret;
> 
> -	return ret;
> +	return fwnode_call_int_op(fwnode->secondary,
> property_read_int_array, propname,
> +				  elem_size, val, nval);
>  }
> 
>  /**
> @@ -371,14 +375,16 @@ int
> fwnode_property_read_string_array(const struct fwnode_handle
> *fwnode,
>  {
>  	int ret;
> 
> +	if (IS_ERR_OR_NULL(fwnode))
> +		return -EINVAL;
> +
>  	ret = fwnode_call_int_op(fwnode,
> property_read_string_array, propname,
>  				 val, nval);
> -	if (ret == -EINVAL && !IS_ERR_OR_NULL(fwnode) &&
> -	    !IS_ERR_OR_NULL(fwnode->secondary))
> -		ret = fwnode_call_int_op(fwnode->secondary,
> -					 property_read_string_array,
> propname,
> -					 val, nval);
> -	return ret;
> +	if (ret != -EINVAL)
> +		return ret;
> +
> +	return fwnode_call_int_op(fwnode->secondary,
> property_read_string_array, propname,
> +				  val, nval);
>  }
>  EXPORT_SYMBOL_GPL(fwnode_property_read_string_array);
> 
> @@ -480,15 +486,16 @@ int
> fwnode_property_get_reference_args(const struct fwnode_handle
> *fwnode,
>  {
>  	int ret;
> 
> +	if (IS_ERR_OR_NULL(fwnode))
> +		return -ENOENT;
> +
>  	ret = fwnode_call_int_op(fwnode, get_reference_args, prop,
> nargs_prop,
>  				 nargs, index, args);
> +	if (ret == 0)
> +		return ret;
> 
> -	if (ret < 0 && !IS_ERR_OR_NULL(fwnode) &&
> -	    !IS_ERR_OR_NULL(fwnode->secondary))
> -		ret = fwnode_call_int_op(fwnode->secondary,
> get_reference_args,
> -					 prop, nargs_prop, nargs, index,
> args);
> -
> -	return ret;
> +	return fwnode_call_int_op(fwnode->secondary,
> get_reference_args, prop, nargs_prop,
> +				  nargs, index, args);
>  }
>  EXPORT_SYMBOL_GPL(fwnode_property_get_reference_args);
> 
> @@ -698,7 +705,7 @@ fwnode_get_next_available_child_node(const
> struct fwnode_handle *fwnode,
>  {
>  	struct fwnode_handle *next_child = child;
> 
> -	if (!fwnode)
> +	if (IS_ERR_OR_NULL(fwnode))
>  		return NULL;
> 
>  	do {
> @@ -722,16 +729,16 @@ struct fwnode_handle
> *device_get_next_child_node(struct device *dev,
>  	const struct fwnode_handle *fwnode = dev_fwnode(dev);
>  	struct fwnode_handle *next;
> 
> +	if (IS_ERR_OR_NULL(fwnode))
> +		return NULL;
> +
>  	/* Try to find a child in primary fwnode */
>  	next = fwnode_get_next_child_node(fwnode, child);
>  	if (next)
>  		return next;
> 
>  	/* When no more children in primary, continue with secondary
> */
> -	if (fwnode && !IS_ERR_OR_NULL(fwnode->secondary))
> -		next = fwnode_get_next_child_node(fwnode-
> >secondary, child);
> -
> -	return next;
> +	return fwnode_get_next_child_node(fwnode->secondary,
> child);
>  }
>  EXPORT_SYMBOL_GPL(device_get_next_child_node);
> 
> @@ -798,6 +805,9 @@ EXPORT_SYMBOL_GPL(fwnode_handle_put);
>   */
>  bool fwnode_device_is_available(const struct fwnode_handle
> *fwnode)
>  {
> +	if (IS_ERR_OR_NULL(fwnode))
> +		return false;
> +
>  	if (!fwnode_has_op(fwnode, device_is_available))
>  		return true;
> 
> @@ -988,14 +998,14 @@ fwnode_graph_get_next_endpoint(const
> struct fwnode_handle *fwnode,
>  		parent = fwnode_graph_get_port_parent(prev);
>  	else
>  		parent = fwnode;
> +	if (IS_ERR_OR_NULL(parent))
> +		return NULL;
> 
>  	ep = fwnode_call_ptr_op(parent, graph_get_next_endpoint,
> prev);
> +	if (ep)
> +		return ep;

I might be missing something but before the check being done was
'if (IS_ERR_OR_NULL(ep)'. Is there anyway for ep to be an error
pointer? Looking at OF, It seems that only NULL or a valid pointer
is being returned. Did not looked at others implementations of
though...

- Nuno Sá