[igt-dev] [PATCH i-g-t] lib/i915/gem_mman: Add support for GEM_MMAP_OFFSET ioctl

[Tvrtko Ursulin]

On 05/12/2019 12:40, Chris Wilson wrote:
> Quoting Zbigniew Kempczyński (2019-12-05 12:31:13)
>> With introduction of new kernel ioctl we need to cover this in
>> the IGT's. Patch adds mmap functions appropriate for this.
>>
>> Signed-off-by: Lukasz Kalamarz <lukasz.kalamarz at intel.com>
>> Signed-off-by: Antonio Argenziano <antonio.argenziano at intel.com>
>> Signed-off-by: Zbigniew Kempczyński <zbigniew.kempczynski at intel.com>
>> Cc: Chris Wilson <chris at chris-wilson.co.uk>
> 
> Do we really have people outside of gem_mmap_wc.c and gem_mmap_offset.c
> that care whether their WC/WB mmapping is provided by MMAP_OFFSET_IOCTL
> or MMAP_IOCTL. They just expect it to work, I would have thought --
> basically just gem_mmap__device_coherent (and maybe the alternative would
> be gem_mmap__cache_coherent, don't quote me on that :)
> 
> It's not a huge deal, I think it falls under overengineering that will
> simply lead to confusion of "when do I use one and not the other?"

What shall we do with call sites which used to do:

   gem_mmap__gtt()
   get_set_domain(GTT)

And now do:

   gem_mmap__device_coherent()
   gem_set_domain(GTT)

?

Sounds like we need a helper to either lets the caller know which 
flavour of mmap was used so correct flushing can be done, or a 
synchronous helper where possible sounds much easier:

   gem_mmap__device_coherent_sync() - does the correct set_domain internally

Regards,

Tvrtko