Re: [PATCH v3] drm/i915: Added write-enable pte bit support

[Akash Goel <akash.goel@intel.com>]

On Wed, 2014-05-14 at 10:14 +0200, Daniel Vetter wrote:
> On Tue, May 13, 2014 at 03:43:12PM -0700, Jesse Barnes wrote:
> > On Wed, 14 May 2014 00:30:34 +0200
> > Daniel Vetter <daniel@ffwll.ch> wrote:
> > 
> > > On Tue, May 13, 2014 at 03:05:24PM -0700, Jesse Barnes wrote:
> > > > On Tue, 11 Feb 2014 14:19:03 +0530
> > > > akash.goel@intel.com wrote:
> > > > 
> > > > > @@ -810,6 +815,7 @@ static void gen6_ppgtt_insert_entries(struct i915_address_space *vm,
> > > > >  		pt_vaddr[act_pte] =
> > > > >  			vm->pte_encode(sg_page_iter_dma_address(&sg_iter),
> > > > >  				       cache_level, true);
> > > > > +
> > > > >  		if (++act_pte == I915_PPGTT_PT_ENTRIES) {
> > > > >  			kunmap_atomic(pt_vaddr);
> > > > >  			pt_vaddr = NULL;
> > > > 
> > > > Some extra whitespace here.

Thanks, will remove this.

> > > > 
> > > > Otherwise:
> > > > Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
> > > 
> > > Hm, looking at the patch again encoding this into the cache_level enum is
> > > fraught with fun. And due to IS_VLV aliasing chv this will blow up on chv
> > > very likely. My old idea was to eventually add a pte_flags param all over
> > > for this stuff with additional bits.
> > 
> > That works too; and yeah CHV is all different here isn't it.  But won't
> > it go through the gen8 paths anyway?
> 
> Yes, but we have a switch on the cache_level in the gen8 pte encode
> function. Since the bit31 gets or'ed in for VLV, it'll hit also chv and
> wreak havoc in that specific switch - we'll hit the default case when we
> don't expect to.
> 
> cache_level = functional behaviour relevant for the kernel's clflushing
> code
> 

As the 'IS_VALLEYVIEW' check will alias with CHV also, can I just update
the condition here, to include 'GEN7' also (IS_GEN7) in the check.

> > Ack on the cache_level abuse though; it's an implementation detail that
> > should be changed if/when this is properly exposed to userspace (or
> > maybe we shouldn't bother and just use CHV/BDW stuff going forward,
> > supporting a proper mprotect ioctl).
> 
> Not talking about exposing to userspace, but adding pte_flags to the
> low-level platform pte encode functions to prevent the above bugs. I'm ok
> with keeping obj->gt_ro.
> -Daniel