linux-kernel - Re: [PATCH v2 10/11] gpiolib: add new ioctl() for monitoring changes in line info

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Date:   Fri, 6 Dec 2019 22:20:42 +0100
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Kent Gibson <warthog618@...il.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 10/11] gpiolib: add new ioctl() for monitoring changes
 in line info

czw., 5 gru 2019 o 18:02 Andy Shevchenko <andy.shevchenko@...il.com> napisał(a):
>
> On Thu, Dec 5, 2019 at 3:47 PM Bartosz Golaszewski <brgl@...ev.pl> wrote:
> > czw., 5 gru 2019 o 11:27 Andy Shevchenko <andy.shevchenko@...il.com> napisał(a):
> > > On Thu, Dec 5, 2019 at 11:42 AM Bartosz Golaszewski
> > > <bgolaszewski@...libre.com> wrote:
> > > > śr., 4 gru 2019 o 23:34 Andy Shevchenko <andy.shevchenko@...il.com> napisał(a):
> > > > > On Wed, Dec 4, 2019 at 6:03 PM Bartosz Golaszewski <brgl@...ev.pl> wrote:
>
> > > So, the test cases, I can imagine of, should include (k - kernel, u - user):
> > > - 64k-64u: LE and BE
> > > - 64k-32u: LE and BE
> > > - 32k-32u: LE and BE
> >
> > I usually use qemu VMs built with yocto for testing but I don't see
> > any way of creating a 32-bit user-space with 64-bit kernel. Any ideas
> > on how to prepare a testing environment?
>
> In my case it's very easy. I do
> - compile kernel as 64-bit separately;
> - compile initramfs of Buildroot distro with external kernel build provided.
>

Any specific config options are needed on x86-64 kernel to use 32-bit
user-space? I'm not well versed in x86 architectures, that's why I'm
asking. I built a 32-bit userspace qemu image with yocto and then
manually built a 64-bit kernel. I tried running it but I'm getting a
kernel panic when the rootfs is being mounted.

On a different note: why would endianness be an issue here? 32-bit
variables with 64-bit alignment should still be in the same place in
memory, right?

Any reason not to use __packed for this structure and not deal with
this whole compat mess?

I also noticed that my change will only allow user-space to read one
event at a time which seems to be a regression with regard to the
current implementation. I probably need to address this too.

Bart

> That's setup in which I observed the issue.
>
> --
> With Best Regards,
> Andy Shevchenko