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

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Message-ID: <CAJ1xhMUhhri8W0EYQqf3ZNJ4BQfbtxB-ONQ1eBNP8cPVW+_VaQ@mail.gmail.com>
Date:   Sat, 6 Jan 2018 21:56:00 +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: Re: [PATCH] vboxvideo: Fix incorrect type in assignment sparse warning

On Sat, Jan 6, 2018 at 9:43 PM, Hans de Goede <hdegoede@...hat.com> wrote:
> 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.

Thanks for confirming my understanding of this.

>
>> What are your thoughts on this?
>
>
> Lets just move ahead with your original fix:

Did you want me to resend the patch, or is someone going to pull the
original one I sent into their tree?
Thanks.

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