On Thu, Jan 12, 2017 at 12:13:51PM +0100, Arnd Bergmann wrote: > The tegra DRM driver is almost ok without an MMU, but there > is one small warning that I get: > > drivers/gpu/drm/tegra/gem.c: In function 'tegra_drm_mmap': > drivers/gpu/drm/tegra/gem.c:508:12: unused variable 'prot' > > This marks the variable as __maybe_unused instead. > > Signed-off-by: Arnd Bergmann <[email protected]> > --- > drivers/gpu/drm/tegra/gem.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/gpu/drm/tegra/gem.c b/drivers/gpu/drm/tegra/gem.c > index 7d853e6b5ff0..63f14b7a59a0 100644 > --- a/drivers/gpu/drm/tegra/gem.c > +++ b/drivers/gpu/drm/tegra/gem.c > @@ -505,7 +505,7 @@ int tegra_drm_mmap(struct file *file, struct > vm_area_struct *vma) > > vma->vm_pgoff = vm_pgoff; > } else { > - pgprot_t prot = vm_get_page_prot(vma->vm_flags); > + pgprot_t prot __maybe_unused = vm_get_page_prot(vma->vm_flags);
This seems to me like a suboptimal solution. The reason why this fails
is because pgprot_writecombine(prot) for NOMMU translates to __pgprot(0)
via a macro. This also means that we need to potentially add a
__maybe_unused annotation to every local variable that stores a value
that gets passed to pgprot_writecombine().
There fortunately aren't very many of those cases, but I still think
that a better solution would be to turn pgprot_writecombine() into a
static inline function, so that the parameter would get silently
ignored. Or perhaps if it must remain a macro, then doing the following
should still avoid the need to modify every call site:
#define pgprot_writecombine(prot) ({ (void)prot; __pgprot(0); })
Thierry
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