linux-kernel - Re: [PATCH v2 05/18] gpiolib: cdev: support GPIO_GET_LINE_IOCTL and GPIOLINE_GET_VALUES

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Message-ID: <20200729022814.GA1750878@sol>
Date:   Wed, 29 Jul 2020 10:28:14 +0800
From:   Kent Gibson <warthog618@...il.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Linus Walleij <linus.walleij@...aro.org>
Subject: Re: [PATCH v2 05/18] gpiolib: cdev: support GPIO_GET_LINE_IOCTL and
 GPIOLINE_GET_VALUES_IOCTL

On Sun, Jul 26, 2020 at 09:12:44AM +0800, Kent Gibson wrote:
> On Sat, Jul 25, 2020 at 11:51:54PM +0300, Andy Shevchenko wrote:
> > On Sat, Jul 25, 2020 at 7:24 AM Kent Gibson <warthog618@...il.com> wrote:
> > >

[ snip ]

> > > +                   test_bit(line_idx, (unsigned long *)lc->attrs[i].mask))
> > 
> > This casting is not good. What about BE 32-bit architecture?
> > 
> 
> I agree the casting is hideous, but I thought the outcome was correct
> as it is manipulating addresses, not data.
> You think the address of a 64-bit differs based on endian??
> Happy to change it - but not sure what to.
> 

You are right - using bitops on u64 is problematic for BE-32 - the 32-bit
words will be swapped if userspace treats the flags as the u64 it is
defined as.

I'll rework that for v3.

Cheers,
Kent.