On 03/18/2017 02:22 PM, Rob Clark wrote:
On Fri, Mar 17, 2017 at 1:39 PM, Oleksandr Andrushchenko
<andr2000@xxxxxxxxx> wrote:
Hello,
I am writing a para-virtualized DRM driver for Xen hypervisor
and it now works with DRM CMA helpers, but I would also like
to make it work with non-contigous memory: virtual machine
that the driver runs in can't guarantee that CMA is actually
physically contigous (that is not a problem because of IPMMU
and other means, the only constraint I have is that I cannot mmap
with pgprot == noncached). So, I am planning to use *drm_gem_get_pages* +
*shmem_read_mapping_page_gfp* to allocate memory for GEM objects
(scanout buffers + dma-bufs shared with virtual GPU)
Do you think this is the right approach to take?
I guess if you had some case where you needed to "migrate" buffers
between host and guest memory, then TTM might be useful. Otherwise
this sounds like the right approach.
Tried that today (drm_gem_get_pages), the result is interesting:
1. modetest
1.1. Runs, I can see page flips
1.2. vm_operations_struct.fault is called, I can vm_insert_page
2. kmscube (Rob, thanks for that :) + PowerVR SGX 6250
2.1. Cannot initialize EGL
2.2. vm_operations_struct.fault is NOT called
In both cases 2 dumbs are created and successfully mmaped,
in case of kmscube there are also handle_to_fd IOCTLs issued
and no DRM errors observed. No DMA-BUF mmap attempt seen
I re-checked 2) with alloc_pages + remap_pfn_range and it works
(it cannot unmap cleanly, but it could be because I didn't call
split_pages after alloc_pages), thus the setup is still good
Can it be that the buffer allocated with drm_gem_get_pages
doesn't suit PowerVR for some reason?
BR,
-R
Thank you,
Oleksandr
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