From: "Rafael J. Wysocki" <rafael@kernel.org>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Sakari Ailus <sakari.ailus@linux.intel.com>,
Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
Heikki Krogerus <heikki.krogerus@linux.intel.com>,
Bjorn Andersson <andersson@kernel.org>,
Prashant Malani <pmalani@chromium.org>,
linux-acpi@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-usb@vger.kernel.org, Daniel Scally <djrscally@gmail.com>,
"Rafael J. Wysocki" <rafael@kernel.org>
Subject: Re: [PATCH v2 1/5] device property: Keep dev_fwnode() and dev_fwnode_const() separate
Date: Mon, 3 Oct 2022 13:54:37 +0200 [thread overview]
Message-ID: <CAJZ5v0hHPjSN-369pagN3Mnxd1yvc6+4YGb0Kpx3=+aahV=AmQ@mail.gmail.com> (raw)
In-Reply-To: <YzcAh/xtqQM1Qin4@kroah.com>
On Fri, Sep 30, 2022 at 4:43 PM Greg Kroah-Hartman
<gregkh@linuxfoundation.org> wrote:
>
> 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@linux.intel.com>
> > > > Fixes: aade55c86033 ("device property: Add const qualifier to device_get_match_data() parameter")
> > > > Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> > > > Acked-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
> > > > Reviewed-by: Sakari Ailus <sakari.ailus@linux.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.
Well, is this really a problem?
After all, if an immutable structure is embedded in another one, that
doesn't automatically imply that the containing structure has to be
immutable too. Hence, a const pointer to the inner structure doesn't
automatically yield a const pointer to the outer one.
> > Being able to turn struct device pointers const is certainly not worth
> > violating constness properties.
>
> Agreed, but we can do better...
next prev parent reply other threads:[~2022-10-03 11:54 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-28 10:57 [PATCH v2 0/5] device property: Consitify a few APIs and correct dev_fwnode() Andy Shevchenko
2022-09-28 10:57 ` [PATCH v2 1/5] device property: Keep dev_fwnode() and dev_fwnode_const() separate Andy Shevchenko
2022-09-28 11:05 ` Greg Kroah-Hartman
2022-09-30 14:30 ` Sakari Ailus
2022-09-30 14:43 ` Greg Kroah-Hartman
2022-10-03 11:02 ` Sakari Ailus
2022-10-03 15:07 ` Greg Kroah-Hartman
2022-10-03 16:17 ` Greg Kroah-Hartman
2022-10-03 20:08 ` Sakari Ailus
2022-10-04 7:55 ` Greg Kroah-Hartman
2022-10-04 8:14 ` Andy Shevchenko
2022-10-04 8:24 ` Greg Kroah-Hartman
2022-10-04 8:25 ` Andy Shevchenko
2022-10-04 9:21 ` Andy Shevchenko
2022-10-04 9:15 ` Sakari Ailus
2022-10-03 11:54 ` Rafael J. Wysocki [this message]
2022-10-03 12:00 ` Sakari Ailus
2022-10-03 15:05 ` Greg Kroah-Hartman
2022-09-28 10:57 ` [PATCH v2 2/5] device property: Constify fwnode connection match APIs Andy Shevchenko
2022-09-28 10:57 ` [PATCH v2 3/5] device property: Constify parameter in fwnode_graph_is_endpoint() Andy Shevchenko
2022-09-28 10:57 ` [PATCH v2 4/5] device property: Constify device child node APIs Andy Shevchenko
2022-09-28 10:57 ` [PATCH v2 5/5] device property: Constify parameter in device_dma_supported() and device_get_dma_attr() Andy Shevchenko
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='CAJZ5v0hHPjSN-369pagN3Mnxd1yvc6+4YGb0Kpx3=+aahV=AmQ@mail.gmail.com' \
--to=rafael@kernel.org \
--cc=andersson@kernel.org \
--cc=andriy.shevchenko@linux.intel.com \
--cc=djrscally@gmail.com \
--cc=gregkh@linuxfoundation.org \
--cc=heikki.krogerus@linux.intel.com \
--cc=linux-acpi@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-usb@vger.kernel.org \
--cc=pmalani@chromium.org \
--cc=sakari.ailus@linux.intel.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).