linux-kernel - Re: [PATCH v2] device property: Get rid of union aliasing

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Message-ID: <ddd9eae5cf848df9c25a49001845a3d80e429a6f.camel@linux.intel.com>
Date:   Mon, 14 May 2018 19:13:24 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Lukas Wunner <lukas@...ner.de>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        linux-efi@...r.kernel.org,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>
Subject: Re: [PATCH v2] device property: Get rid of union aliasing

On Mon, 2018-05-14 at 17:40 +0200, Lukas Wunner wrote:
> On Mon, May 14, 2018 at 03:48:09PM +0300, Andy Shevchenko wrote:
> > On Mon, 2018-05-14 at 14:18 +0200, Lukas Wunner wrote:
> > > On Tue, May 08, 2018 at 04:15:47PM +0300, Andy Shevchenko wrote:
> > > > --- a/drivers/firmware/efi/apple-properties.c
> > > > +++ b/drivers/firmware/efi/apple-properties.c
> > > > @@ -13,6 +13,9 @@
> > > > + * FIXME: The approach is still based on union aliasing and
> > > > should be
> > > > + * replaced by a proper resource provider.
> > > 
> > > Why?  All Apple EFI properties are either boolean or u8 arrays.
> > > You've correctly changed this file to always supply u8 arrays,
> > > so I don't see where union aliasing is happening here?
> > 
> > Okay, for now I can see only Thunderbolt user of these properties
> > (is it
> > correct?) in upstream which uses u8 arrays indeed.
> 
> That is correct, thunderbolt.ko is so far the only user.
> 
> 
> > Though the implementation is quite fragile in this sense, because it
> > doesn't discourage people to use device_property_read_string() in
> > case
> > when it's indeed a string (I saw these kind of properties in the
> > very
> > dump you posted on your GH page).
> 
> Well if that is your concern then you need to prevent functions which
> retrieve properties to use the wrong type.
> 
> E.g. to prevent retrieval of the u8 array as string, you'd have to
> amend drivers/base/property.c:pset_prop_read_string_array() to
> check the type of the property found and return -EINVAL if it's not
> string.

I think it's doable. I will hack a new version later this week.

But it still not a (best) solution for Apple properties. B/c as I told
already I saw in _your_ dump the _string_ properties. Someone might have
got an idea to use them as _strings_.

-- 
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Intel Finland Oy