Re: [Intel-gfx] [PATCH 21/23] drm/i915: Add support for FBs requiring a POT stride alignment

[Imre Deak <imre.deak@intel.com>]

On Fri, Mar 12, 2021 at 08:02:36PM +0200, Ville Syrjälä wrote:
> [...]
> On Thu, Mar 11, 2021 at 12:17:34AM +0200, Imre Deak wrote:
> > diff --git a/drivers/gpu/drm/i915/display/intel_display_types.h b/drivers/gpu/drm/i915/display/intel_display_types.h
> > index fc02eca45e4d..08b348c9e3e1 100644
> > --- a/drivers/gpu/drm/i915/display/intel_display_types.h
> > +++ b/drivers/gpu/drm/i915/display/intel_display_types.h
> > @@ -94,6 +94,7 @@ struct intel_framebuffer {
> >  	struct drm_framebuffer base;
> >  	struct intel_frontbuffer *frontbuffer;
> >  	struct intel_rotation_info rot_info;
> > +	struct intel_remapped_info rem_info;
> >  
> >  	/* for each plane in the normal GTT view */
> >  	struct {
> > @@ -101,6 +102,8 @@ struct intel_framebuffer {
> >  	} normal[4];
> >  	/* for each plane in the rotated GTT view for no-CCS formats */
> >  	struct intel_fb_plane_remap_info rotated[2];
> > +	/* for each plane in the remapped GTT view. TODO: CCS formats */
> > +	struct intel_fb_plane_remap_info remapped[2];
> 
> We might want to look into restructuring this a it as a followup.
> Maybe we can collect all the rotation vs. remapping stuff into
> separate sub-structures. Not sure.

Do you mean

 struct intel_fb_plane_remap_info {
+       struct intel_remapped_plane_info gtt;
        unsigned int x, y;
        unsigned int pitch; /* pixels */
 };
@@ -93,8 +94,6 @@ struct intel_fb_plane_remap_info {
 struct intel_framebuffer {
        struct drm_framebuffer base;
        struct intel_frontbuffer *frontbuffer;
-       struct intel_rotation_info rot_info;
-       struct intel_remapped_info rem_info;
 
        /* for each plane in the normal GTT view */
        struct {

resulting in
https://github.com/ideak/linux/commit/0fd28d738f9

?

Looks better to me.

> [...] 
> > +static unsigned int plane_view_dst_stride(const struct intel_framebuffer *fb, int color_plane,
> > +					  int pitch_tiles)
> > +{
> > +	unsigned int dst_stride;
> > +
> > +	if (!intel_fb_needs_pot_stride_remap(fb)) {
> > +		dst_stride = pitch_tiles;
> > +	} else {
> > +		dst_stride = roundup_pow_of_two(pitch_tiles);
> > +		drm_WARN_ON(fb->base.dev, dst_stride < pitch_tiles);
> 
> Dunno if that WARN is particularly useful. We're talking in tiles here
> so seems extremely unlikely it could overflow.
> 
> So I'd probably just make this as simple as possible, like:
> if (needs_pot)
> 	return roundup(x);
> else
> 	return x;

Ok, maybe I was thinking of u16, but the overflow for that is checked
later.

I'll also s/int pitch_tiles/unsigned int pitch_tiles/.

> > +	};
> > +
> > +	return dst_stride;
> > +}
> > +
> [...]
> > @@ -1280,9 +1282,27 @@ rotate_pages(struct drm_i915_gem_object *obj, unsigned int offset,
> >  			sg_dma_address(sg) =
> >  				i915_gem_object_get_dma_address(obj, src_idx);
> >  			sg_dma_len(sg) = I915_GTT_PAGE_SIZE;
> > +
> >  			sg = sg_next(sg);
> > -			src_idx -= stride;
> > +			src_idx -= src_stride;
> >  		}
> > +
> > +		left = (dst_stride - height) * I915_GTT_PAGE_SIZE;
> > +
> > +		if (!left)
> > +			continue;
> > +
> > +		st->nents++;
> > +
> > +		/*
> > +		 * The DE ignores the PTEs for the padding tiles, the sg entry
> > +		 * here is just a conenience to indicate how many padding PTEs
> > +		 * to insert at this spot.
> > +		 */
> 
> OK. That certainly makes this nice and simple.

This was only confirmed to be the case on ADL_P, but that's the only
relevant place in any case.

> > +		sg_set_page(sg, NULL, left, 0);
> > +		sg_dma_address(sg) = 0;
> > +		sg_dma_len(sg) = left;
> > +		sg = sg_next(sg);
> 
> Do we have enough sg entries for these extras? Ah, yeah we allocate
> based on the worst case where each vma page needs its own entry.

Yes, and then i915_sg_trim() compacts it.

> Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> 
> >  	}
> >  
> >  	return sg;
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