linux-kernel - Re: [PATCH v2 1/5] device property: Keep dev_fwnode() and dev_fwnode

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Date:   Wed, 28 Sep 2022 13:05:20 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Bjorn Andersson <andersson@...nel.org>,
        Prashant Malani <pmalani@...omium.org>,
        linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-usb@...r.kernel.org, Daniel Scally <djrscally@...il.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>
Subject: Re: [PATCH v2 1/5] device property: Keep dev_fwnode() and
 dev_fwnode_const() separate

On Wed, Sep 28, 2022 at 01:57:42PM +0300, Andy Shevchenko wrote:
> It's not fully correct to take a const parameter pointer to a struct
> and return a non-const pointer to a member of that struct.
> 
> Instead, introduce a const version of the dev_fwnode() API which takes
> and returns const pointers and use it where it's applicable.
> 
> Suggested-by: Sakari Ailus <sakari.ailus@...ux.intel.com>
> Fixes: aade55c86033 ("device property: Add const qualifier to device_get_match_data() parameter")
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> Acked-by: Heikki Krogerus <heikki.krogerus@...ux.intel.com>
> Reviewed-by: Sakari Ailus <sakari.ailus@...ux.intel.com>
> ---
>  drivers/base/property.c  | 11 +++++++++--
>  include/linux/property.h |  3 ++-
>  2 files changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/base/property.c b/drivers/base/property.c
> index 4d6278a84868..699f1b115e0a 100644
> --- a/drivers/base/property.c
> +++ b/drivers/base/property.c
> @@ -17,13 +17,20 @@
>  #include <linux/property.h>
>  #include <linux/phy.h>
>  
> -struct fwnode_handle *dev_fwnode(const struct device *dev)
> +struct fwnode_handle *dev_fwnode(struct device *dev)
>  {
>  	return IS_ENABLED(CONFIG_OF) && dev->of_node ?
>  		of_fwnode_handle(dev->of_node) : dev->fwnode;
>  }
>  EXPORT_SYMBOL_GPL(dev_fwnode);
>  
> +const struct fwnode_handle *dev_fwnode_const(const struct device *dev)
> +{
> +	return IS_ENABLED(CONFIG_OF) && dev->of_node ?
> +		of_fwnode_handle(dev->of_node) : dev->fwnode;
> +}
> +EXPORT_SYMBOL_GPL(dev_fwnode_const);

Ick, no, this is a mess.

Either always return a const pointer, or don't.  Ideally always return a
const pointer, so all we really need is:

const struct fwnode_handle *dev_fwnode(const struct device *dev);

right?

Yes, it will take some unwinding backwards to get there, but please do
that instead of having 2 different functions where the parameter type is
part of the function name.  This isn't the 1980's...

thanks,

greg k-h