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

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Message-ID: <6f4de025-b126-9819-d789-ef611c9f82d9@redhat.com>
Date:   Sat, 6 Jan 2018 20:43:59 +0100
From:   Hans de Goede <hdegoede@...hat.com>
To:     Alexander Kapshuk <alexander.kapshuk@...il.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: Re: [PATCH] vboxvideo: Fix incorrect type in assignment sparse
 warning

HI,

On 06-01-18 20:30, Alexander Kapshuk wrote:
> 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?

No your not misreading this I did not check the function myself before
commenting myself, my bad.

> What are your thoughts on this?

Lets just move ahead with your original fix:

Reviewed-by: Hans de Goede <hdegoede@...hat.com>

Regards,

Hans