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

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@xxxxxxx> 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?


Calling this vmap instead of kmap certainly makes sense.
Not 100% sure about the generic helpers, but it sounds like this should indeed look rather clean in the end. 

Christian.



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@xxxxxxx>
---
     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

 

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