Re: [PATCH 7/8] drm/i915: fixup the initial fb base on DG1

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Mon, Mar 07, 2022 at 06:26:32PM +0000, Matthew Auld wrote:
> On 07/03/2022 17:06, Ville Syrjälä wrote:
> > On Mon, Mar 07, 2022 at 10:32:36AM +0000, Matthew Auld wrote:
> >> On 04/03/2022 19:33, Ville Syrjälä wrote:
> >>> On Fri, Mar 04, 2022 at 05:23:32PM +0000, Matthew Auld wrote:
> >>>> The offset we get looks to be the exact start of DSM, but the
> >>>> inital_plane_vma expects the address to be relative.
> >>>>
> >>>> Signed-off-by: Matthew Auld <matthew.auld@intel.com>
> >>>> Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> >>>> ---
> >>>>    .../drm/i915/display/intel_plane_initial.c    | 22 +++++++++++++++----
> >>>>    1 file changed, 18 insertions(+), 4 deletions(-)
> >>>>
> >>>> diff --git a/drivers/gpu/drm/i915/display/intel_plane_initial.c b/drivers/gpu/drm/i915/display/intel_plane_initial.c
> >>>> index f797fcef18fc..b39d3a8dfe45 100644
> >>>> --- a/drivers/gpu/drm/i915/display/intel_plane_initial.c
> >>>> +++ b/drivers/gpu/drm/i915/display/intel_plane_initial.c
> >>>> @@ -56,10 +56,24 @@ initial_plane_vma(struct drm_i915_private *i915,
> >>>>    	if (!mem || plane_config->size == 0)
> >>>>    		return NULL;
> >>>>    
> >>>> -	base = round_down(plane_config->base,
> >>>> -			  I915_GTT_MIN_ALIGNMENT);
> >>>> -	size = round_up(plane_config->base + plane_config->size,
> >>>> -			mem->min_page_size);
> >>>> +	base = plane_config->base;
> >>>> +	if (IS_DGFX(i915)) {
> >>>> +		/*
> >>>> +		 * On discrete the base address should be somewhere in LMEM, but
> >>>> +		 * depending on the size of LMEM the base address might
> >>>> +		 * intersect with the start of DSM, like on DG1, in which case
> >>>> +		 * we need the relative address. In such cases we might also
> >>>> +		 * need to choose between inital fb vs fbc, if space is limited.
> >>>> +		 *
> >>>> +		 * On future discrete HW, like DG2, we should be able to just
> >>>> +		 * allocate directly from LMEM, due to larger LMEM size.
> >>>> +		 */
> >>>> +		if (base >= i915->dsm.start)
> >>>> +			base -= i915->dsm.start;
> >>>
> >>> Subsequent code expects the object to actually be inside stolen.
> >>> If that is not the case we should just give up.
> >>
> >> Thanks for taking a look at this. Is that subsequent code outside
> >> initial_plane_vma()? In the next patch this is now using LMEM directly
> >> for dg2. Would that blow up somewhere else?
> > 
> > It uses i915_gem_object_create_stolen_for_preallocated() which assumes
> > the stuff is inside stolen.
> 
> At the start of the series that gets ripped out and replaced with 
> i915_gem_object_create_region_at(), where we can now just pass in the 
> intel_memory_region, and the backend hopefully takes care of the rest.

Why? Is the BIOS no longer allocating its fbs from stolen?

> 
> > 
> >>> The fact that we fail to confirm any of that on integrated
> >>> parts has always bugged me, but not enough to actually do
> >>> anything about it. Such a check would be somewhat more involved
> >>> since we'd have to look at the PTEs. But on discrete sounds like
> >>> we can get away with a trivial check.
> >>
> >> Which PTEs?
> > 
> > The PTEs the plane is actually using. We have no idea where they
> > actually point to and just assume they represent a 1:1 mapping of
> > stolen.
> > 
> > I suppose with lmem we'll just start assuming a 1:1 mapping of
> > the whole lmem rather than just stolen.
> 
> So IIUC the base that we read is actually some GGTT address(I guess it 
> comes pre-programmed or something?), and that hopefully 1:1 maps to 
> stolen. Ok, so as you say, I guess we only want to subtract the 
> dsm.start for the physical allocation, and not the GGTT address, when 
> dealing with stolen lmem.
> 
> > 

-- 
Ville Syrjälä
Intel