Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <20200802005458-mutt-send-email-mst@kernel.org> <CAHp75Vfwhfrse47jRR9msFHA4ZqoVvE8RYHZNKxu-_ZiGyS9Sw@mail.gmail.com>
In-Reply-To: <CAHp75Vfwhfrse47jRR9msFHA4ZqoVvE8RYHZNKxu-_ZiGyS9Sw@mail.gmail.com>
From:   Arnd Bergmann <arnd@arndb.de>
Date:   Sun, 2 Aug 2020 12:48:33 +0200
Message-ID: <CAK8P3a0-gQEH3NpYUx=aFg6U8LagfYKuXqMMH4MvVS4SmaghOg@mail.gmail.com>
Subject: Re: sparse warnings in vop
To:     Andy Shevchenko <andy.shevchenko@gmail.com>
Cc:     "Michael S. Tsirkin" <mst@redhat.com>,
        "sudeep.dutt@intel.com" <sudeep.dutt@intel.com>,
        "ashutosh.dixit@intel.com" <ashutosh.dixit@intel.com>,
        "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Sun, Aug 2, 2020 at 9:25 AM Andy Shevchenko
<andy.shevchenko@gmail.com> wrote:
> On Sunday, August 2, 2020, Michael S. Tsirkin <mst@redhat.com> wrote:
>>
>> Hi!
>> Building vop with make C=1 produces the following:
>>
>> CHECK   drivers/misc/mic/vop/vop_main.c
>> drivers/misc/mic/vop/vop_main.c:551:58: warning: incorrect type in argument 1 (different address spaces)
>> drivers/misc/mic/vop/vop_main.c:551:58:    expected void const volatile [noderef] __iomem *addr
>> drivers/misc/mic/vop/vop_main.c:551:58:    got restricted __le64 *
>> drivers/misc/mic/vop/vop_main.c:560:49: warning: incorrect type in argument 1 (different address spaces)
>> drivers/misc/mic/vop/vop_main.c:560:49:    expected struct mic_device_ctrl *dc
>> drivers/misc/mic/vop/vop_main.c:560:49:    got struct mic_device_ctrl [noderef] __iomem *dc
>> drivers/misc/mic/vop/vop_main.c:579:49: warning: incorrect type in argument 1 (different address spaces)
>> drivers/misc/mic/vop/vop_main.c:579:49:    expected struct mic_device_ctrl *dc
>> drivers/misc/mic/vop/vop_main.c:579:49:    got struct mic_device_ctrl [noderef] __iomem *dc
>>
>> Would be nice to fix to silence the noise, but I'm not 100% sure
>> what the right thing to do here is. Tag struct members with __iomem or
>> cast with __force on use?
>
>
>
> Sounds right to me.

I don't think either of the above, adding __force is almost always wrong,
and __iomem never applies to struct members, only to pointers.

The first problem I see is with:

static struct _vop_vdev *vop_dc_to_vdev(struct mic_device_ctrl *dc)

The argument needs to be an __iomem pointer. In the structure, the
first member has type __le64, which gets mentioned in the warning.
We usually use __u64 instead (or don't use structures at all for __iomem
operations), but I don't think this would cause a warning if the argument
is fixed.

Then there is the question of why in the world you would have an MMIO
register contain a kernel pointer, but that is more a driver design question
than something that causes a warning.

      Arnd