Re: [PATCH 4/9] drm/i915: Introduce fb->min_alignment

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

On Tue, May 28, 2024 at 02:27:52PM +0300, Imre Deak wrote:
> On Mon, May 13, 2024 at 08:59:37PM +0300, Ville Syrjala wrote:
> > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > 
> > Different planes could have different alignment requirements
> > even for the same format/modifier. Collect the alignment
> > requirements across all planes capable of scanning out the
> > fb such that the alignment used when pinning the normal ggtt
> > view is satisfactory to all those planes.
> > 
> > When pinning per-plane views we only have to satisfy the
> > alignment requirements of the specific plane.
> > 
> > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > ---
> >  .../drm/i915/display/intel_display_types.h    |  2 ++
> >  drivers/gpu/drm/i915/display/intel_fb.c       | 23 ++++++++++++++++
> >  drivers/gpu/drm/i915/display/intel_fb_pin.c   | 27 +++++++++++++++++--
> >  drivers/gpu/drm/i915/display/intel_fbdev.c    | 18 +------------
> >  4 files changed, 51 insertions(+), 19 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/display/intel_display_types.h b/drivers/gpu/drm/i915/display/intel_display_types.h
> > index 40d6e5f4c350..58bb65832adf 100644
> > --- a/drivers/gpu/drm/i915/display/intel_display_types.h
> > +++ b/drivers/gpu/drm/i915/display/intel_display_types.h
> > @@ -145,6 +145,8 @@ struct intel_framebuffer {
> >  	};
> >  
> >  	struct i915_address_space *dpt_vm;
> > +
> > +	unsigned int min_alignment;
> >  };
> >  
> >  enum intel_hotplug_state {
> > diff --git a/drivers/gpu/drm/i915/display/intel_fb.c b/drivers/gpu/drm/i915/display/intel_fb.c
> > index 3f3a9cd534f4..c5bae05cbbc3 100644
> > --- a/drivers/gpu/drm/i915/display/intel_fb.c
> > +++ b/drivers/gpu/drm/i915/display/intel_fb.c
> > @@ -10,6 +10,7 @@
> >  #include <linux/dma-resv.h>
> >  
> >  #include "i915_drv.h"
> > +#include "intel_atomic_plane.h"
> >  #include "intel_display.h"
> >  #include "intel_display_types.h"
> >  #include "intel_dpt.h"
> > @@ -1616,6 +1617,26 @@ bool intel_fb_supports_90_270_rotation(const struct intel_framebuffer *fb)
> >  	       fb->base.modifier == I915_FORMAT_MOD_Yf_TILED;
> >  }
> >  
> > +static unsigned int intel_fb_min_alignment(const struct drm_framebuffer *fb)
> > +{
> > +	struct drm_i915_private *i915 = to_i915(fb->dev);
> > +	struct intel_plane *plane;
> > +	unsigned int min_alignment = 0;
> > +
> > +	for_each_intel_plane(&i915->drm, plane) {
> > +		if (!drm_plane_has_format(&plane->base, fb->format->format, fb->modifier))
> > +			continue;
> > +
> > +		if (intel_plane_needs_physical(plane))
> > +			continue;
> > +
> > +		min_alignment = max(min_alignment,
> > +				    plane->min_alignment(plane, fb, 0));
> > +	}
> > +
> > +	return min_alignment;
> > +}
> > +
> >  int intel_fill_fb_info(struct drm_i915_private *i915, struct intel_framebuffer *fb)
> >  {
> >  	struct drm_i915_gem_object *obj = intel_fb_obj(&fb->base);
> > @@ -1698,6 +1719,8 @@ int intel_fill_fb_info(struct drm_i915_private *i915, struct intel_framebuffer *
> >  		return -EINVAL;
> >  	}
> >  
> > +	fb->min_alignment = intel_fb_min_alignment(&fb->base);
> > +
> >  	return 0;
> >  }
> >  
> > diff --git a/drivers/gpu/drm/i915/display/intel_fb_pin.c b/drivers/gpu/drm/i915/display/intel_fb_pin.c
> > index 9b0f1ea41b70..1ae02de906f5 100644
> > --- a/drivers/gpu/drm/i915/display/intel_fb_pin.c
> > +++ b/drivers/gpu/drm/i915/display/intel_fb_pin.c
> > @@ -230,13 +230,36 @@ void intel_fb_unpin_vma(struct i915_vma *vma, unsigned long flags)
> >  	i915_vma_put(vma);
> >  }
> >  
> > +static bool gtt_view_is_per_plane(const struct intel_plane_state *plane_state)
> > +{
> > +	const struct intel_framebuffer *fb = to_intel_framebuffer(plane_state->hw.fb);
> > +
> > +	if (plane_state->view.gtt.type == I915_GTT_VIEW_REMAPPED &&
> > +	    intel_fb_needs_pot_stride_remap(fb))
> > +		return false;
> 
> The above view is created only once for the FB, I suppose this is how
> you differentiate it from views created each time due to a stride
> limit (based on intel_plane_needs_remap()).
> 
> > +
> > +	return plane_state->view.gtt.type != I915_GTT_VIEW_NORMAL;
> 
> So the rotated and remapped views created for a stride limit are
> per-plane based on the above. There is also a rotated view created only
> once for the FB, is it intentional to regard this kind of view as
> per-plane as well?

No. Forgot those exist. I guess I should just remove this per-plane
alignment logic for now. Need to think of a proper way to add it back,
or just quietly bury the whole idea.

> 
> > +}
> > +
> >  static unsigned int
> >  intel_plane_fb_min_alignment(const struct intel_plane_state *plane_state)
> >  {
> >  	struct intel_plane *plane = to_intel_plane(plane_state->uapi.plane);
> > -	const struct drm_framebuffer *fb = plane_state->hw.fb;
> > +	const struct intel_framebuffer *fb = to_intel_framebuffer(plane_state->hw.fb);
> >  
> > -	return plane->min_alignment(plane, fb, 0);
> > +	/*
> > +	 * Only use plane specific alignment for binding
> > +	 * a per-plane gtt view (remapped or rotated),
> > +	 * otherwise make sure the alignment is suitable
> > +	 * for all planes.
> > +	 */
> > +	if (!gtt_view_is_per_plane(plane_state))
> > +		return fb->min_alignment;
> > +
> > +	if (intel_plane_needs_physical(plane))
> > +		return 0;
> 
> I guess the above is ok, though looks like an unrelated change: the
> cursor plane min_alignment() for relevant platforms is <= 4k, which will
> be rounded up to 4k anyway when binding the vma.

When intel_plane_needs_physical()==true the alignment declared
by the plane only applies to the physical/dma address, as that
is what the hardware will consume. Doesn't actually matter
where it gets bound in the ggtt.

> 
> > +
> > +	return plane->min_alignment(plane, &fb->base, 0);
> 
> The commit could've had more details about the rational for the above.
> As I understand it avoids having to rebind the vma for different plane
> types, though this is already handled to some degree by
> i915_vma::display_alignment.

It was also semi-handled by intel_surf_alignment() trying to
return the max alignment for all the planes more or less.
But it was a fairly big mess.

I did't really remember that the display_alignment
thing even exists. Hmm. I wonder if it's even needed 
anymore. I suppose we can have cases where the display was
previously using the vma, which was subsequency unbound,
and later rebound due to some other reason. We probably
want to preserve the alignment to make sure it'll again
be ready to be used by the display without an extra
rebind.  I guess that only really happens with pre-ppgtt
platforms and/or software rendering via ggtt.

Hmm. We could perpaps change the implementation to adjust
display_alignment when the framebuffer is created instead
of doing it when the vma actually gets pinned. Might not
matter for real world uses cases though.

> 
> >  }
> >  
> >  static unsigned int
> > diff --git a/drivers/gpu/drm/i915/display/intel_fbdev.c b/drivers/gpu/drm/i915/display/intel_fbdev.c
> > index ff685aebbd1a..124aac172acb 100644
> > --- a/drivers/gpu/drm/i915/display/intel_fbdev.c
> > +++ b/drivers/gpu/drm/i915/display/intel_fbdev.c
> > @@ -46,7 +46,6 @@
> >  #include "gem/i915_gem_mman.h"
> >  
> >  #include "i915_drv.h"
> > -#include "intel_crtc.h"
> >  #include "intel_display_types.h"
> >  #include "intel_fb.h"
> >  #include "intel_fb_pin.h"
> > @@ -172,21 +171,6 @@ static const struct fb_ops intelfb_ops = {
> >  
> >  __diag_pop();
> >  
> > -static unsigned int intel_fbdev_min_alignment(const struct drm_framebuffer *fb)
> > -{
> > -	struct drm_i915_private *i915 = to_i915(fb->dev);
> > -	struct intel_plane *plane;
> > -	struct intel_crtc *crtc;
> > -
> > -	crtc = intel_first_crtc(i915);
> > -	if (!crtc)
> > -		return 0;
> > -
> > -	plane = to_intel_plane(crtc->base.primary);
> > -
> > -	return plane->min_alignment(plane, fb, 0);
> > -}
> > -
> >  static int intelfb_create(struct drm_fb_helper *helper,
> >  			  struct drm_fb_helper_surface_size *sizes)
> >  {
> > @@ -244,7 +228,7 @@ static int intelfb_create(struct drm_fb_helper *helper,
> >  	 * BIOS is suitable for own access.
> >  	 */
> >  	vma = intel_fb_pin_to_ggtt(&fb->base, &view,
> > -				   intel_fbdev_min_alignment(&fb->base), 0,
> > +				   fb->min_alignment, 0,
> >  				   false, &flags);
> >  	if (IS_ERR(vma)) {
> >  		ret = PTR_ERR(vma);
> > -- 
> > 2.43.2
> > 

-- 
Ville Syrjälä
Intel