linux-kernel - Re: [PATCH v7 1/3] devres: provide devm

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Message-ID: <CAMRc=Md5yrgxnPf=qwKYhwHACcq-XeKOKZ76OwYdMGO8SgYmzQ@mail.gmail.com>
Date:   Tue, 18 Aug 2020 18:27:12 +0200
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Jonathan Cameron <jic23@...nel.org>,
        Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        Michal Simek <michal.simek@...inx.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Guenter Roeck <linux@...ck-us.net>,
        linux-iio <linux-iio@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>
Subject: Re: [PATCH v7 1/3] devres: provide devm_krealloc()

On Tue, Aug 18, 2020 at 10:40 AM Andy Shevchenko
<andriy.shevchenko@...ux.intel.com> wrote:
>
> On Mon, Aug 17, 2020 at 10:02:05PM +0200, Bartosz Golaszewski wrote:
> > On Mon, Aug 17, 2020 at 7:43 PM Andy Shevchenko
> > <andriy.shevchenko@...ux.intel.com> wrote:
> > > On Mon, Aug 17, 2020 at 07:05:33PM +0200, Bartosz Golaszewski wrote:
> > > > From: Bartosz Golaszewski <bgolaszewski@...libre.com>
>
> ...
>
> > > > +static struct devres *to_devres(void *data)
> > > > +{
> > > > +     return (struct devres *)((u8 *)data - ALIGN(sizeof(struct devres),
> > > > +                                                 ARCH_KMALLOC_MINALIGN));
> > >
> > > Do you really need both explicit castings?
> > >
> >
> > Yeah, we can probably drop the (struct devres *) here.
>
> void * -> u8 * here is also not needed, it is considered byte access IIRC.
>

Actually it turns out that while we don't need the (void *) -> (u8 *)
casting, we must cast to (struct devres *) or the following error is
produced:

drivers/base/devres.c: In function ‘to_devres’:
drivers/base/devres.c:41:21: error: returning ‘u8 *’ {aka ‘unsigned
char *’} from a function with incompatible return type ‘struct devres
*’ [-Werror=incompatible-pointer-types]
  return ((u8 *)data - ALIGN(sizeof(struct devres),
         ~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
        ARCH_KMALLOC_MINALIGN));
        ~~~~~~~~~~~~~~~~~~~~~~~

Bart