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

[Thomas Zimmermann <tzimmermann@suse.de>]

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Hi

Am 07.10.20 um 15:10 schrieb Daniel Vetter:
> 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?

The calls to ttm_bo_kmap/_kunmap() require an instance of struct
ttm_bo_kmap_obj that is stored in each driver's private bo structure
(e.g., struct drm_gem_vram_object, struct radeon_bo, etc). When I made
patch 3, I flirted with the idea of unifying the driver's _vmap code in
a shared helper, but I couldn't find a simple way of doing it. That's
why it's open-coded in the first place.

Best regards
Thomas

> -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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>>>>>>>>>> _______________________________________________
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>>>>>>>>> _______________________________________________
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>>>>>>>>>
>>>>>>>> _______________________________________________
>>>>>>>> amd-gfx mailing list
>>>>>>>> amd-gfx@lists.freedesktop.org
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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
>>
> 
> 

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


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