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SubjectRe: DMA-buf and uncached system memory
From
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Hi

Am 15.02.21 um 10:49 schrieb Thomas Zimmermann:
> Hi
>
> Am 15.02.21 um 09:58 schrieb Christian König:
>> Hi guys,
>>
>> we are currently working an Freesync and direct scan out from system
>> memory on AMD APUs in A+A laptops.
>>
>> On problem we stumbled over is that our display hardware needs to scan
>> out from uncached system memory and we currently don't have a way to
>> communicate that through DMA-buf.

Re-reading this paragrah, it sounds more as if you want to let the
exporter know where to move the buffer. Is this another case of the
missing-pin-flag problem?

Best regards
Thomas

>>
>> For our specific use case at hand we are going to implement something
>> driver specific, but the question is should we have something more
>> generic for this?
>
> For vmap operations, we return the address as struct dma_buf_map, which
> contains additional information about the memory buffer. In vram
> helpers, we have the interface drm_gem_vram_offset() that returns the
> offset of the GPU device memory.
>
> Would it be feasible to combine both concepts into a dma-buf interface
> that returns the device-memory offset plus the additional caching flag?
>
> There'd be a structure and a getter function returning the structure.
>
> struct dma_buf_offset {
>     bool cached;
>     u64 address;
> };
>
> // return offset in *off
> int dma_buf_offset(struct dma_buf *buf, struct dma_buf_off *off);
>
> Whatever settings are returned by dma_buf_offset() are valid while the
> dma_buf is pinned.
>
> Best regards
> Thomas
>
>>
>> After all the system memory access pattern is a PCIe extension and as
>> such something generic.
>>
>> Regards,
>> Christian.
>> _______________________________________________
>> dri-devel mailing list
>> dri-devel@lists.freedesktop.org
>> https://lists.freedesktop.org/mailman/listinfo/dri-devel
>
>
> _______________________________________________
> dri-devel mailing list
> dri-devel@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel
>

--
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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