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

[Hans de Goede]

HI,

On 06-01-18 20:30, Alexander Kapshuk wrote:
> On Sat, Jan 6, 2018 at 6:00 PM, Hans de Goede <hdegoede@xxxxxxxxxx> 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@xxxxxxxxx>
> > > > ---
> > > >    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@xxxxxxxxxx>

Regards,

Hans