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

Daniel Vetter
2020-10-07T13:11:04Z

On Wed, Oct 7, 2020 at 2:57 PM Thomas Zimmermann <tzimmermann@suse.de> wrote:
>
> Hi
>
> Am 02.10.20 um 11:58 schrieb Daniel Vetter:
> > 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 agree on the goals, but what is the immediate objective here?
>
> Adding ttm_bo_vmap() does not work out easily, as struct ttm_bo_kmap_obj
> is a central part of the internals of TTM. struct ttm_bo_kmap_obj has
> more internal state that struct dma_buf_map, so they are not easily
> convertible either. What you propose seems to require a reimplementation
> of the existing ttm_bo_kmap() code. That is it's own patch series.
>
> I'd rather go with some variant of the existing patch and add
> ttm_bo_vmap() in a follow-up.

ttm_bo_vmap would simply wrap what you currently open-code as
ttm_bo_kmap + ttm_kmap_obj_to_dma_buf_map. Removing ttm_kmap_obj would
be a much later step. Why do you think adding ttm_bo_vmap is not
possible?
-Daniel

> Best regards
> Thomas
>
> >
> > 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
> >
>
> --
> Thomas Zimmermann
> Graphics Driver Developer
> SUSE Software Solutions Germany GmbH
> Maxfeldstr. 5, 90409 Nürnberg, Germany
> (HRB 36809, AG Nürnberg)
> Geschäftsführer: Felix Imendörffer
>

--
Daniel Vetter
Software Engineer, Intel Corporation