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

[Chris Wilson]

On Tue, Jul 21, 2015 at 04:17:05PM +0200, Daniel Vetter wrote:
> 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!

In a few years, when mmu-notifiers are enabled by default.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre