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Message-ID: <YzcAh/xtqQM1Qin4@kroah.com> Date: Fri, 30 Sep 2022 16:43:19 +0200 From: Greg Kroah-Hartman <gregkh@...uxfoundation.org> To: Sakari Ailus <sakari.ailus@...ux.intel.com> Cc: Andy Shevchenko <andriy.shevchenko@...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 Fri, Sep 30, 2022 at 02:30:53PM +0000, Sakari Ailus wrote: > Hi Greg, > > On Wed, Sep 28, 2022 at 01:05:20PM +0200, Greg Kroah-Hartman wrote: > > 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... > > The problem with this approach is that sometimes non-const fwnode_handles > are needed. On OF, for instance, anything that has something to do with > refcounting requires this. Software nodes as well. If they are writable, then yes, let's keep them writable, and not create two function paths where we have to pick and choose. > One option which I suggested earlier was to turn dev_fwnode() into a macro > and use C11 _Generic() to check whether the device is const or not. As much fun as that would be, I don't think it would work well. Although, maybe it would, have an example of how that would look? I ask as I just went through a large refactoring of the kobject layer to mark many things const * and I find it a bit "sad" that functions like this: static inline struct device *kobj_to_dev(const struct kobject *kobj) { return container_of(kobj, struct device, kobj); } have the ability to take a read-only pointer and spit out a writable one thanks to the pointer math in container_of() with no one being the wiser. > Being able to turn struct device pointers const is certainly not worth > violating constness properties. Agreed, but we can do better... thanks, greg k-h
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