[PATCH 0/7] [RFC] drm/exynos: Add IOMMU support to DRM

[Inki Dae]

> -----Original Message-----
> From: Subash Patel [mailto:subash.ramaswamy at linaro.org]
> Sent: Friday, July 13, 2012 3:58 PM
> To: Inki Dae
> Cc: 'Prathyush K'; dri-devel at lists.freedesktop.org;
prathyush at chromium.org;
> m.szyprowski at samsung.com
> Subject: Re: [PATCH 0/7] [RFC] drm/exynos: Add IOMMU support to DRM
> 
> On 07/13/2012 12:09 PM, Inki Dae wrote:
> >
> >> -----Original Message-----
> >> From: Prathyush K [mailto:prathyush.k at samsung.com]
> >> Sent: Wednesday, July 11, 2012 6:40 PM
> >> To: dri-devel at lists.freedesktop.org
> >> Cc: prathyush at chromium.org; m.szyprowski at samsung.com;
> > inki.dae at samsung.com;
> >> subash.ramaswamy at linaro.org
> >> Subject: [PATCH 0/7] [RFC] drm/exynos: Add IOMMU support to DRM
> >>
> >> The dma-mapping framework needs a IOMMU mapping to be created for the
> >> device which allocates/maps/frees the non-contig buffer. In the DRM
> >> framework, a gem buffer is created by the DRM virtual device and not
> >> directly by any of the physical devices (FIMD, HDMI etc). Each gem
> object
> >> can be set as a framebuffer to one or many of the drm devices. So a gem
> >> object cannot be allocated for any one device. All the DRM devices
> should
> >> be able to access this buffer.
> >>
> > It's good to use unified iommu table so I agree to your opinion but we
> don't
> > decide whether we use dma mapping api or not. now dma mapping api has
> one
> > issue.
> > in case of using iommu with dma mapping api, we couldn't use physically
> > contiguous memory region with iommu. for this, there is a case that we
> > should use physically contiguous memory region with iommu. it is because
> we
> > sometime may use mfc(hw video codec) with secure zone such as ARM
> TrustZone.
> > Then, it needs physically contiguous memory region.
> >
> > Thanks,
> > Inki Dae
> I agree. In the mainline code, as of now only the arm_dma_ops has the
> support allocating
> from the CMA. But in the function arm_iommu_alloc_attrs(), there is no
> way to know if the
> device had declared a contiguous memory range. The reason, we don't
> store that cookie
> into the device during the dma_declare_contiguous(). So is it advisable
> to store such information
> like mapping(in the iommu operations) in the device.archdata?
> 
> Regards,
> Subash

There was my missing point. dma mapping api with iommu tries to allocate
pages contiguously if possible. as HW Video codec above, there is the case
that physically contiguous memory region is need necessarily but it seems
like that now dma mapping api doesn't guarantee fully physically contiguous
memory region(for example, if physically contiguous memory allocation is
failed then it should return an error so that we can check it)

Marek, for this, could you please give us comments?

Thanks,
Inki Dae

> >
> >> The proposed method is to create a common IOMMU mapping during drm
init.
> >> This
> >> mapping is then attached to all of the drm devices including the drm
> >> device.
> >> [PATCH 1/7] drm/exynos: create common IOMMU mapping for DRM
> >>
> >> During the probe of drm fimd, the driver retrieves a 'sysmmu' field
> >> in the device node for fimd. If such a field exists, the driver
> retrieves
> >> the
> >> platform device of the sysmmu device. This sysmmu is set as the sysmmu
> >> for fimd. The common mapping created is then attached to fimd.
> >> This needs to be done for all the other devices (hdmi, vidi etc).
> >> [PATCH 2/7] ARM: EXYNOS5: add sysmmu field to fimd device node
> >> [PATCH 3/7] drm/exynos: add IOMMU support to drm fimd
> >>
> >> During DRM's probe which happens last, the common mapping is set to its
> >> archdata
> >> and iommu ops are set as its dma ops. This requires a modification in
> the
> >> dma-mapping framework so that the iommu ops can be visible to all
> drivers.
> >> [PATCH 4/7] ARM: dma-mapping: rename and export iommu_ops
> >> [PATCH 5/7] drm/exynos: attach drm device with common drm mapping
> >>
> >> Currently allocation and free use the iommu framework by calling
> >> dma_alloc_writecombine and dma_free_writecombine respectively.
> >> For mapping the buffers to user space, the mmap functions assume that
> >> the buffer is contiguous. This is modified by calling
> >> dma_mmap_writecombine.
> >> [PATCH 6/7] drm/exynos: Add exynos drm specific fb_mmap function
> >> [PATCH 7/7] Add IOMMU support for mapping gem object
> >>
> >> The device tree based patches are based on Leela's patch which was
> posted
> >> last week for adding DT support to DRM FIMD. The patch to add sysmmu
> >> field is for reference only and will be posted to the device tree
> >> mailing list. Same with the rename and export iommu_ops patch.
> >>
> >> These patches are tested on Exynos5250 SMDK board and tested with
> modetest
> >> from libdrm tests.
> >>
> >> Prathyush K (7):
> >>    drm/exynos: create common IOMMU mapping for DRM
> >>    ARM: EXYNOS5: add sysmmu field to fimd device node
> >>    drm/exynos: add IOMMU support to drm fimd
> >>    ARM: dma-mapping: rename and export iommu_ops
> >>    drm/exynos: attach drm device with common drm mapping
> >>    drm/exynos: Add exynos drm specific fb_mmap function
> >>    drm/exynos: Add IOMMU support for mapping gem object
> >>
> >>   arch/arm/boot/dts/exynos5250.dtsi         |    1 +
> >>   arch/arm/include/asm/dma-mapping.h        |    1 +
> >>   arch/arm/mm/dma-mapping.c                 |    5 ++-
> >>   drivers/gpu/drm/exynos/exynos_drm_core.c  |    3 ++
> >>   drivers/gpu/drm/exynos/exynos_drm_drv.c   |   30 ++++++++++++++++
> >>   drivers/gpu/drm/exynos/exynos_drm_drv.h   |   10 +++++
> >>   drivers/gpu/drm/exynos/exynos_drm_fbdev.c |   16 ++++++++
> >>   drivers/gpu/drm/exynos/exynos_drm_fimd.c  |   54
> >> ++++++++++++++++++++++++++++-
> >>   drivers/gpu/drm/exynos/exynos_drm_gem.c   |   35 ++++++++----------
> >>   9 files changed, 133 insertions(+), 22 deletions(-)