Re: [PATCH v3 2/7] drm/ttm: Add ttm_kmap_obj_to_dma_buf_map() for type conversion

Daniel Vetter
2020-10-02T09:58:44Z

On Wed, Sep 30, 2020 at 02:51:46PM +0200, Daniel Vetter wrote:
> On Wed, Sep 30, 2020 at 2:34 PM Christian König
> <christian.koenig@amd.com> wrote:
> >
> > Am 30.09.20 um 11:47 schrieb Daniel Vetter:
> > > On Wed, Sep 30, 2020 at 10:34:31AM +0200, Christian König wrote:
> > >> Am 30.09.20 um 10:19 schrieb Thomas Zimmermann:
> > >>> Hi
> > >>>
> > >>> Am 30.09.20 um 10:05 schrieb Christian König:
> > >>>> Am 29.09.20 um 19:49 schrieb Thomas Zimmermann:
> > >>>>> Hi Christian
> > >>>>>
> > >>>>> Am 29.09.20 um 17:35 schrieb Christian König:
> > >>>>>> Am 29.09.20 um 17:14 schrieb Thomas Zimmermann:
> > >>>>>>> The new helper ttm_kmap_obj_to_dma_buf() extracts address and location
> > >>>>>>> from and instance of TTM's kmap_obj and initializes struct dma_buf_map
> > >>>>>>> with these values. Helpful for TTM-based drivers.
> > >>>>>> We could completely drop that if we use the same structure inside TTM as
> > >>>>>> well.
> > >>>>>>
> > >>>>>> Additional to that which driver is going to use this?
> > >>>>> As Daniel mentioned, it's in patch 3. The TTM-based drivers will
> > >>>>> retrieve the pointer via this function.
> > >>>>>
> > >>>>> I do want to see all that being more tightly integrated into TTM, but
> > >>>>> not in this series. This one is about fixing the bochs-on-sparc64
> > >>>>> problem for good. Patch 7 adds an update to TTM to the DRM TODO list.
> > >>>> I should have asked which driver you try to fix here :)
> > >>>>
> > >>>> In this case just keep the function inside bochs and only fix it there.
> > >>>>
> > >>>> All other drivers can be fixed when we generally pump this through TTM.
> > >>> Did you take a look at patch 3? This function will be used by VRAM
> > >>> helpers, nouveau, radeon, amdgpu and qxl. If we don't put it here, we
> > >>> have to duplicate the functionality in each if these drivers. Bochs
> > >>> itself uses VRAM helpers and doesn't touch the function directly.
> > >> Ah, ok can we have that then only in the VRAM helpers?
> > >>
> > >> Alternative you could go ahead and use dma_buf_map in ttm_bo_kmap_obj
> > >> directly and drop the hack with the TTM_BO_MAP_IOMEM_MASK.
> > >>
> > >> What I want to avoid is to have another conversion function in TTM because
> > >> what happens here is that we already convert from ttm_bus_placement to
> > >> ttm_bo_kmap_obj and then to dma_buf_map.
> > > Hm I'm not really seeing how that helps with a gradual conversion of
> > > everything over to dma_buf_map and assorted helpers for access? There's
> > > too many places in ttm drivers where is_iomem and related stuff is used to
> > > be able to convert it all in one go. An intermediate state with a bunch of
> > > conversions seems fairly unavoidable to me.
> >
> > Fair enough. I would just have started bottom up and not top down.
> >
> > Anyway feel free to go ahead with this approach as long as we can remove
> > the new function again when we clean that stuff up for good.
>
> Yeah I guess bottom up would make more sense as a refactoring. But the
> main motivation to land this here is to fix the __mmio vs normal
> memory confusion in the fbdev emulation helpers for sparc (and
> anything else that needs this). Hence the top down approach for
> rolling this out.

Ok I started reviewing this a bit more in-depth, and I think this is a bit
too much of a de-tour.

Looking through all the callers of ttm_bo_kmap almost everyone maps the
entire object. Only vmwgfx uses to map less than that. Also, everyone just
immediately follows up with converting that full object map into a
pointer.

So I think what we really want here is:
- new function

int ttm_bo_vmap(struct ttm_buffer_object *bo, struct dma_buf_map *map);

_vmap name since that's consistent with both dma_buf functions and
what's usually used to implement this. Outside of the ttm world kmap
usually just means single-page mappings using kmap() or it's iomem
sibling io_mapping_map* so rather confusing name for a function which
usually is just used to set up a vmap of the entire buffer.

- a helper which can be used for the drm_gem_object_funcs vmap/vunmap
functions for all ttm drivers. We should be able to make this fully
generic because a) we now have dma_buf_map and b) drm_gem_object is
embedded in the ttm_bo, so we can upcast for everyone who's both a ttm
and gem driver.

This is maybe a good follow-up, since it should allow us to ditch quite
a bit of the vram helper code for this more generic stuff. I also might
have missed some special-cases here, but from a quick look everything
just pins the buffer to the current location and that's it.

Also this obviously requires Christian's generic ttm_bo_pin rework
first.

- roll the above out to drivers.

Christian/Thomas, thoughts on this?

I think for the immediate need of rolling this out for vram helpers and
fbdev code we should be able to do this, but just postpone the driver wide
roll-out for now.

Cheers, Daniel

> -Daniel
>
> >
> > Christian.
> >
> > > -Daniel
> > >
> > >> Thanks,
> > >> Christian.
> > >>
> > >>> Best regards
> > >>> Thomas
> > >>>
> > >>>> Regards,
> > >>>> Christian.
> > >>>>
> > >>>>> Best regards
> > >>>>> Thomas
> > >>>>>
> > >>>>>> Regards,
> > >>>>>> Christian.
> > >>>>>>
> > >>>>>>> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
> > >>>>>>> ---
> > >>>>>>> include/drm/ttm/ttm_bo_api.h | 24 ++++++++++++++++++++++++
> > >>>>>>> include/linux/dma-buf-map.h | 20 ++++++++++++++++++++
> > >>>>>>> 2 files changed, 44 insertions(+)
> > >>>>>>>
> > >>>>>>> diff --git a/include/drm/ttm/ttm_bo_api.h b/include/drm/ttm/ttm_bo_api.h
> > >>>>>>> index c96a25d571c8..62d89f05a801 100644
> > >>>>>>> --- a/include/drm/ttm/ttm_bo_api.h
> > >>>>>>> +++ b/include/drm/ttm/ttm_bo_api.h
> > >>>>>>> @@ -34,6 +34,7 @@
> > >>>>>>> #include <drm/drm_gem.h>
> > >>>>>>> #include <drm/drm_hashtab.h>
> > >>>>>>> #include <drm/drm_vma_manager.h>
> > >>>>>>> +#include <linux/dma-buf-map.h>
> > >>>>>>> #include <linux/kref.h>
> > >>>>>>> #include <linux/list.h>
> > >>>>>>> #include <linux/wait.h>
> > >>>>>>> @@ -486,6 +487,29 @@ static inline void *ttm_kmap_obj_virtual(struct
> > >>>>>>> ttm_bo_kmap_obj *map,
> > >>>>>>> return map->virtual;
> > >>>>>>> }
> > >>>>>>> +/**
> > >>>>>>> + * ttm_kmap_obj_to_dma_buf_map
> > >>>>>>> + *
> > >>>>>>> + * @kmap: A struct ttm_bo_kmap_obj returned from ttm_bo_kmap.
> > >>>>>>> + * @map: Returns the mapping as struct dma_buf_map
> > >>>>>>> + *
> > >>>>>>> + * Converts struct ttm_bo_kmap_obj to struct dma_buf_map. If the memory
> > >>>>>>> + * is not mapped, the returned mapping is initialized to NULL.
> > >>>>>>> + */
> > >>>>>>> +static inline void ttm_kmap_obj_to_dma_buf_map(struct ttm_bo_kmap_obj
> > >>>>>>> *kmap,
> > >>>>>>> + struct dma_buf_map *map)
> > >>>>>>> +{
> > >>>>>>> + bool is_iomem;
> > >>>>>>> + void *vaddr = ttm_kmap_obj_virtual(kmap, &is_iomem);
> > >>>>>>> +
> > >>>>>>> + if (!vaddr)
> > >>>>>>> + dma_buf_map_clear(map);
> > >>>>>>> + else if (is_iomem)
> > >>>>>>> + dma_buf_map_set_vaddr_iomem(map, (void __force __iomem *)vaddr);
> > >>>>>>> + else
> > >>>>>>> + dma_buf_map_set_vaddr(map, vaddr);
> > >>>>>>> +}
> > >>>>>>> +
> > >>>>>>> /**
> > >>>>>>> * ttm_bo_kmap
> > >>>>>>> *
> > >>>>>>> diff --git a/include/linux/dma-buf-map.h b/include/linux/dma-buf-map.h
> > >>>>>>> index fd1aba545fdf..2e8bbecb5091 100644
> > >>>>>>> --- a/include/linux/dma-buf-map.h
> > >>>>>>> +++ b/include/linux/dma-buf-map.h
> > >>>>>>> @@ -45,6 +45,12 @@
> > >>>>>>> *
> > >>>>>>> * dma_buf_map_set_vaddr(&map. 0xdeadbeaf);
> > >>>>>>> *
> > >>>>>>> + * To set an address in I/O memory, use dma_buf_map_set_vaddr_iomem().
> > >>>>>>> + *
> > >>>>>>> + * .. code-block:: c
> > >>>>>>> + *
> > >>>>>>> + * dma_buf_map_set_vaddr_iomem(&map. 0xdeadbeaf);
> > >>>>>>> + *
> > >>>>>>> * Test if a mapping is valid with either dma_buf_map_is_set() or
> > >>>>>>> * dma_buf_map_is_null().
> > >>>>>>> *
> > >>>>>>> @@ -118,6 +124,20 @@ static inline void dma_buf_map_set_vaddr(struct
> > >>>>>>> dma_buf_map *map, void *vaddr)
> > >>>>>>> map->is_iomem = false;
> > >>>>>>> }
> > >>>>>>> +/**
> > >>>>>>> + * dma_buf_map_set_vaddr_iomem - Sets a dma-buf mapping structure to
> > >>>>>>> an address in I/O memory
> > >>>>>>> + * @map: The dma-buf mapping structure
> > >>>>>>> + * @vaddr_iomem: An I/O-memory address
> > >>>>>>> + *
> > >>>>>>> + * Sets the address and the I/O-memory flag.
> > >>>>>>> + */
> > >>>>>>> +static inline void dma_buf_map_set_vaddr_iomem(struct dma_buf_map *map,
> > >>>>>>> + void __iomem *vaddr_iomem)
> > >>>>>>> +{
> > >>>>>>> + map->vaddr_iomem = vaddr_iomem;
> > >>>>>>> + map->is_iomem = true;
> > >>>>>>> +}
> > >>>>>>> +
> > >>>>>>> /**
> > >>>>>>> * dma_buf_map_is_equal - Compares two dma-buf mapping structures
> > >>>>>>> for equality
> > >>>>>>> * @lhs: The dma-buf mapping structure
> > >>>>>> _______________________________________________
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>
>
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch

--
Daniel Vetter
Software Engineer, Intel Corporation