Re: [PATCH] media: staging: ipu3: Enable IOVA API only when IOMMU support is enabled

[Robin Murphy]

On 24/07/2019 15:09, Dmitry Osipenko wrote:
> 24.07.2019 17:03, Yuehaibing ÐÐÑÐÑ:
> > On 2019/7/24 21:49, Robin Murphy wrote:
> > > On 24/07/2019 11:30, Sakari Ailus wrote:
> > > > Hi Yue,
> > > >
> > > > On Mon, Jul 22, 2019 at 09:47:49PM +0800, YueHaibing wrote:
> > > > > If IOMMU_SUPPORT is not set, ipu3 driver may select IOMMU_IOVA to m.
> > > > > But for many drivers, they use "select IOMMU_IOVA if IOMMU_SUPPORT"
> > > > > in the Kconfig, for example, CONFIG_TEGRA_VDE is set to y but IOMMU_IOVA
> > > > > is m, then the building fails like this:
> > > > >
> > > > > drivers/staging/media/tegra-vde/iommu.o: In function `tegra_vde_iommu_map':
> > > > > iommu.c:(.text+0x41): undefined reference to `alloc_iova'
> > > > > iommu.c:(.text+0x56): undefined reference to `__free_iova'
> > > > >
> > > > > Reported-by: Hulk Robot <hulkci@xxxxxxxxxx>
> > > > > Fixes: 7fc7af649ca7 ("media: staging/intel-ipu3: Add imgu top level pci device driver")
> > > > > Signed-off-by: YueHaibing <yuehaibing@xxxxxxxxxx>
> > > > > ---
> > > > >    drivers/staging/media/ipu3/Kconfig | 2 +-
> > > > >    1 file changed, 1 insertion(+), 1 deletion(-)
> > > > >
> > > > > diff --git a/drivers/staging/media/ipu3/Kconfig b/drivers/staging/media/ipu3/Kconfig
> > > > > index 4b51c67..b7df18f 100644
> > > > > --- a/drivers/staging/media/ipu3/Kconfig
> > > > > +++ b/drivers/staging/media/ipu3/Kconfig
> > > > > @@ -4,7 +4,7 @@ config VIDEO_IPU3_IMGU
> > > > >        depends on PCI && VIDEO_V4L2
> > > > >        depends on MEDIA_CONTROLLER && VIDEO_V4L2_SUBDEV_API
> > > > >        depends on X86
> > > > > -    select IOMMU_IOVA
> > > > > +    select IOMMU_IOVA if IOMMU_SUPPORT
> > > >
> > > > This doesn't seem right: the ipu3-cio2 driver needs IOMMU_IOVA
> > > > independently of IOMMU_SUPPORT.
> > > >
> > > > Looking at tegra-vde, it seems to depend on IOMMU_SUPPORT but that's not
> > > > declared in its Kconfig entry. I wonder if adding that would be the right
> > > > way to fix this.
> > > >
> > > > Cc'ing the IOMMU list.
> IOMMU_SUPPORT is optional for the Tegra-VDE driver.
>
> > > Right, I also had the impression that we'd made the IOVA library completely standalone. And what does the IPU3 driver's Kconfig have to do with some *other* driver failing to link anyway?
>
> I can see it failing if IPU3 is compiled as a loadable module, while
> Tegra-VDE is a built-in driver. Hence IOVA lib should be also a kernel
> module and thus the IOVA symbols will be missing during of linkage of
> the VDE driver.
>
> > Oh, I misunderstand that IOMMU_IOVA is depend on IOMMU_SUPPORT, thank you for clarification.
> >
> > I will try to fix this in tegra-vde.
>
> Probably IOVA could be selected independently of IOMMU_SUPPORT, but IOVA
> library isn't needed for the VDE driver if IOMMU_SUPPORT is disabled.

Oh, I think I get the problem now - tegra-vde/iommu.c is built 
unconditionally and relies on the static inline stubs for IOMMU and IOVA 
calls if !IOMMU_SUPPORT, but in a compile-test config where IOVA=m for 
other reasons, it then picks up the real declarations from linux/iova.h 
instead of the stubs, and things go downhill from there. So there is a 
real issue, but indeed it's Tegra-VDE which needs to be restructured to 
cope with such configurations, and not IPU3's (or anyone else who may 
select IOVA=m in future) job to work around it.

Robin.