Re: GEM allocation for para-virtualized DRM driver

[Oleksandr Andrushchenko <andr2000@gmail.com>]

Hi, Rob

On 03/18/2017 02:22 PM, Rob Clark wrote:
> On Fri, Mar 17, 2017 at 1:39 PM, Oleksandr Andrushchenko
> <andr2000@gmail.com> 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,
yes, this is the case. but, I can "map" buffers between host and guests

>   then TTM might be useful.
I was looking into it, but it seems to be an overkill in my case
And isn't it that GEM should be used for new drivers, not TTM?
>    Otherwise
> this sounds like the right approach.
Thank you. Actually, I am playing with alloc_pages + remap_pfn_range now,
but what DRM provides (_get_pages + shmem_read) seem to be more portable
and generic. So, I'll probably stick to it
> BR,
> -R
Thank you for helping,
Oleksandr Andrushchenko
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