[Intel-gfx] [PATCH igt] tests/gem_workarounds: Skip write only registers

[Chris Wilson]

Quoting Mika Kuoppala (2017-09-28 14:45:06)
> We have no means to check write only registers as
> this would need access through context image. For now we
> know that cnl has a one such register, 0xe5f0 which is used
> to set WaForceContextSaveRestoreNonCoherent:cnl. By inspecting
> the context image without and with workaround applied:
> 
> 0x0000a840: 0x0000e5f0 0xffff0800
> 0x0000a840: 0x0000e5f0 0xffff0820
> 
> we can conclude that the workaround setup is working right
> in this particular case.
> 
> Add a write only list and add register 0xe5f0 into this list.
> This is a temporary solution until a more capable context image
> checker emerges.
> 
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=102943
> Cc: Oscar Mateo <oscar.mateo at intel.com>
> Cc: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Rodrigo Vivi <rodrigo.vivi at intel.com>
> Signed-off-by: Mika Kuoppala <mika.kuoppala at linux.intel.com>

It makes sense given the discovery of the w/o register. I was thinking
of how we could communicate these through the debugfs, but I think any
changes in direction involve pulling this test into the kernel. So, this
appears to be the pragmatic solution.

Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>
-Chris