linux-kernel - [PATCH] vboxvideo: Fix incorrect type in assignment sparse warning

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Date:   Sat, 6 Jan 2018 21:30:01 +0200
From:   Alexander Kapshuk <alexander.kapshuk@...il.com>
To:     Hans de Goede <hdegoede@...hat.com>
Cc:     Greg KH <gregkh@...uxfoundation.org>, michael.thayer@...cle.com,
        dri-devel@...ts.freedesktop.org, peda@...ntia.se,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Cihangir Aktürk <cakturk@...il.com>,
        Sean Paul <seanpaul@...omium.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: [PATCH] vboxvideo: Fix incorrect type in assignment sparse warning

On Sat, Jan 6, 2018 at 6:00 PM, Hans de Goede <hdegoede@...hat.com> wrote:
> Hi,
>
>
> On 06-01-18 15:20, Alexander Kapshuk wrote:
>>
>> On Mon, Dec 25, 2017 at 04:42:59PM +0200, Alexander Kapshuk wrote:
>>>
>>> Sparse emitted the following warning:
>>> ../drivers/staging/vboxvideo/vbox_fb.c:173:27: warning: incorrect type in
>>> assignment (different address spaces)
>>> ../drivers/staging/vboxvideo/vbox_fb.c:173:27:    expected char [noderef]
>>> <asn:2>*screen_base
>>> ../drivers/staging/vboxvideo/vbox_fb.c:173:27:    got void *virtual
>>>
>>> The vbox_bo buffer object kernel mapping is handled by a call
>>> to ttm_bo_kmap() prior to the assignment of bo->kmap.virtual to
>>> info->screen_base of type char __iomem*.
>>> Casting bo->kmap.virtual to char __iomem* in this assignment fixes
>>> the warning.
>>>
>>> vboxvideo: Fix address space of expression removal sparse warning
>>>
>>> Sparse emitted the following warning:
>>> ../drivers/staging/vboxvideo/vbox_main.c:64:25: warning: cast removes
>>> address space of expression
>>>
>>> vbox->vbva_buffers iomapping is handled by calling vbox_accel_init()
>>> from vbox_hw_init().
>>> __force attribute is used in assignment to vbva to fix the warning.
>>>
>>> Signed-off-by: Alexander Kapshuk <alexander.kapshuk@...il.com>
>>> ---
>>>   drivers/staging/vboxvideo/vbox_fb.c   | 2 +-
>>>   drivers/staging/vboxvideo/vbox_main.c | 2 +-
>>>   2 files changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/staging/vboxvideo/vbox_fb.c
>>> b/drivers/staging/vboxvideo/vbox_fb.c
>>> index 8aed248db6e2..43c39eca4ae1 100644
>>> --- a/drivers/staging/vboxvideo/vbox_fb.c
>>> +++ b/drivers/staging/vboxvideo/vbox_fb.c
>>> @@ -170,7 +170,7 @@ static int vboxfb_create(struct drm_fb_helper
>>> *helper,
>>>         drm_fb_helper_fill_var(info, &fbdev->helper, sizes->fb_width,
>>>                                sizes->fb_height);
>>>
>>> -       info->screen_base = bo->kmap.virtual;
>>> +       info->screen_base = (char __iomem *)bo->kmap.virtual;
>>>         info->screen_size = size;
>>>
>>>   #ifdef CONFIG_DRM_KMS_FB_HELPER
>
>
> This fix looks good to me.
>
>>> diff --git a/drivers/staging/vboxvideo/vbox_main.c
>>> b/drivers/staging/vboxvideo/vbox_main.c
>>> index 80bd039fa08e..973b3bcc04b1 100644
>>> --- a/drivers/staging/vboxvideo/vbox_main.c
>>> +++ b/drivers/staging/vboxvideo/vbox_main.c
>>> @@ -61,7 +61,7 @@ void vbox_enable_accel(struct vbox_private *vbox)
>>>                 if (vbox->vbva_info[i].vbva)
>>>                         continue;
>>>
>>> -               vbva = (void *)vbox->vbva_buffers + i *
>>> VBVA_MIN_BUFFER_SIZE;
>>> +               vbva = (void __force *)vbox->vbva_buffers + i *
>>> VBVA_MIN_BUFFER_SIZE;
>>>                 if (!vbva_enable(&vbox->vbva_info[i],
>>>                                  vbox->guest_pool, vbva, i)) {
>>>                         /* very old host or driver error. */
>
>
> Hmm, isn't there a cleaner way to fix this ? Maybe make vbva_enable's
> argument (and the local vbva variable) of type u8 __iomem * too ?
>
> Regards,
>
> Hans

Hi Hans,

Thanks for your prompt response.

I had a good look at the vbva_enable() function's definition and to
the best of my knowledge, changing vbva's type from 'struct
vbva_buffer *' to 'u8 __iomem *' wouldn't work.
vbva_enable() relies on vbva's type being a pointer to 'struct vbva_buffer':
vbva's memory gets set to zero;
some of vbva's members are initialised to particular values;
vbva_ctx->vbva expects vbva to be a pointer to 'struct vbva_buffer' as well;

Or am I misreading this?
What are your thoughts on this?
Thanks.

Alexander.