Hi

Am 15.02.21 um 10:49 schrieb Thomas Zimmermann:

Hi

Am 15.02.21 um 09:58 schrieb Christian König:

quoted

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

quoted

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

quoted

After all the system memory access pattern is a PCIe extension and as 
such something generic.

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