[Intel-gfx] [PATCH] drm/i915: Add an optional selection from i915 of CONFIG_MMU_NOTIFIER

[Daniel Vetter]

On Tue, Jul 21, 2015 at 01:31:47PM +0100, Tvrtko Ursulin wrote:
> 
> On 07/21/2015 01:16 PM, Chris Wilson wrote:
> >userptr requires mmu-notifier for full unprivileged support. Most
> >systems have mmu-notifier support already enabled as a requirement for
> >virtualisation support, but we should make the option for i915 to take
> >advantage of mmu-notifiers explicit (and enable by default so that
> >regular userspace can take advantage of passing client memory to the
> >GPU.)
> >
> >Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> >---
> >  drivers/gpu/drm/i915/Kconfig | 11 +++++++++++
> >  1 file changed, 11 insertions(+)
> >
> >diff --git a/drivers/gpu/drm/i915/Kconfig b/drivers/gpu/drm/i915/Kconfig
> >index eb87e2538861..1e33195e4a12 100644
> >--- a/drivers/gpu/drm/i915/Kconfig
> >+++ b/drivers/gpu/drm/i915/Kconfig
> >@@ -62,3 +62,14 @@ config DRM_I915_PRELIMINARY_HW_SUPPORT
> >  	  option changes the default for that module option.
> >
> >  	  If in doubt, say "N".
> >+
> >+config DRM_I915_USERPTR
> >+	bool "Always enable userptr support"
> >+	depends on DRM_I915
> >+	select MMU_NOTIFIER
> >+	default y
> >+	help
> >+	  This option selects CONFIG_MMU_NOTIFIER if it isn't already
> >+	  selected to enabled full userptr support.
> 
> s/enabled/enable/
> 
> I think it needs more text under help to explain what are you giving up if
> N, or to justify Y in other words. For distro kernels it is irrelevant but
> advanced users will want to know.
> 
> But since overall I think it is justified, in principle:
> 
> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>

Why not just select MMU_NOTIFIER and be done? Yes there's more overhead
but apparently everyone wants them anyway, so I don't see much point. And
it would give us nicely uniform test coverage, yay!
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch