On 03/20/2017 08:17 PM, Rob Clark wrote:
On Mon, Mar 20, 2017 at 2:01 PM, Oleksandr Andrushchenko
<andr2000@xxxxxxxxx> wrote:
On 03/20/2017 07:38 PM, Rob Clark wrote:
On Mon, Mar 20, 2017 at 1:18 PM, Oleksandr Andrushchenko
<andr2000@xxxxxxxxx> wrote:
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
jfwiw, pages will only get faulted in when CPU accesses them..
indeed, good catch
modetest "renders" the frame on the CPU but kmscube does it on gpu.
yes, I have already learned that modetest only renders once and
then just flips
So not seeing vm_operations_struct.fault is normal. The EGL fail is
not..
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?
I've no idea what the state of things is w/ pvr as far as gbm support
(not required/used by modetest, but anything that uses the gpu on
"bare metal" needs it). Or what the state of dmabuf-import is with
pvr.
Do you think there could be DMA related problems with
the buffer allocated with drm_gem_get_pages and DMA mapping,
use? So GPU is not able to handle those?
The only source of knowledge at the moment I have is
publicly available pvrsrvkm kernel module. But there are
other unknowns, e.g. user-space libraries, firmware which
are in binary form: thus kernel driver is mostly a bridge
between FW and libs. That being said, do you think I have to get
deeper into GPU use-case or should I switch back to alloc_pages+
remap_pfn_range? ;)
so, I suppose with pvr there is a whole host of potential pain... *but*..
if alloc_pages path actually works, then perhaps the issue is the
deferred allocation. Ie. most drivers don't drm_gem_get_pages() until
the buffer is passed to hw or until it is faulted in. You should make
sure it ends up getting called (if it hasn't been called already)
somewhere in gem_prime_pin.
I call drm_gem_get_pages as part of dumb creation, because I
need to pass the pages to the host OS. So, probably, this is not
because of the late allocation, but something else
BR,
-R
Thank you!
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