Re: [PATCH 2/3] drm/i915: fix CFB size calculation

Ville Syrjälä
2015-10-01T12:14:17Z

On Wed, Sep 30, 2015 at 05:05:44PM -0300, Paulo Zanoni wrote:
> We were considering the whole framebuffer height, but the spec says we
> should only consider the active display height size. There were still
> some unclear questions based on the spec, but the hardware guys
> clarified them for us. According to them:
>
> - CFB size = CFB stride * Number of lines FBC writes to CFB
> - CFB stride = plane stride / compression limit
> - Number of lines FBC writes to CFB = MIN(plane source height, maximum
> number of lines FBC writes to CFB)
> - Plane source height =
> - pipe source height (PIPE_SRCSZ register) (before SKL)
> - plane size register height (PLANE_SIZE register) (SKL+)
> - Maximum number of lines FBC writes to CFB =
> - plane source height (before HSW)
> - 2048 (HSW+)
>
> For the plane source height, I could just have made our code do
> I915_READ() in order to be more future proof, but since it's not cool
> to do register reads I decided to just recalculate the values we use
> when we actually write to those registers.
>
> With this patch, depending on your machine configuration, a lot of the
> kms_frontbuffer_tracking subtests that used to result in a SKIP due to
> not enough stolen memory still start resulting in a PASS.
>
> v2: Use the clipped src size instead of pipe_src_h (Ville).
> v3: Use the appropriate information provided by the hardware guys.
>
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
> ---
> drivers/gpu/drm/i915/intel_fbc.c | 58 +++++++++++++++++++++++++++++++++++++---
> 1 file changed, 54 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_fbc.c b/drivers/gpu/drm/i915/intel_fbc.c
> index 1b2ebb2..d53f73f 100644
> --- a/drivers/gpu/drm/i915/intel_fbc.c
> +++ b/drivers/gpu/drm/i915/intel_fbc.c
> @@ -698,9 +698,60 @@ void intel_fbc_cleanup_cfb(struct drm_i915_private *dev_priv)
> mutex_unlock(&dev_priv->fbc.lock);
> }
>
> -static int intel_fbc_setup_cfb(struct drm_i915_private *dev_priv, int size,
> - int fb_cpp)
> +/*
> + * For SKL+, the plane source size used by the hardware is based on the value we
> + * write to the PIPE_SIZE register. For BDW-, the hardware looks at the value we
> + * wrote to PIPESRC.
> + */
> +static void intel_fbc_get_plane_source_sizes(struct intel_crtc *crtc,
> + int *width, int *height)

size in my mind already includes width and height, so plural _sizes
doesn't make much sense to me.

> {
> + struct drm_i915_private *dev_priv = crtc->base.dev->dev_private;
> + struct intel_plane_state *plane_state =
> + to_intel_plane_state(crtc->base.primary->state);
> + int w, h;
> +
> + if (INTEL_INFO(dev_priv)->gen >= 9) {
> + if (intel_rotation_90_or_270(plane_state->base.rotation)) {
> + w = drm_rect_height(&plane_state->src) >> 16;
> + h = drm_rect_width(&plane_state->src) >> 16;
> + } else {
> + w = drm_rect_width(&plane_state->src) >> 16;
> + h = drm_rect_height(&plane_state->src) >> 16;
> + }

You can just use this same code for all platforms.

Actually I'm not sure what we should do wrt. rotation. Do we support
FBC with 90/270 degree rotation? The scanout happens in a rotated
fashion, so swapping the dimensions like you do would seem like the
right thing. But not sure.

> + } else {
> + w = crtc->config->pipe_src_w;
> + h = crtc->config->pipe_src_h;
> + }
> +
> + if (width)
> + *width = w;
> + if (height)
> + *height = h;
> +}
> +
> +static int intel_fbc_calculate_cfb_size(struct intel_crtc *crtc)
> +{
> + struct drm_i915_private *dev_priv = crtc->base.dev->dev_private;
> + struct drm_framebuffer *fb = crtc->base.primary->fb;
> + int lines;
> +
> + intel_fbc_get_plane_source_sizes(crtc, NULL, &lines);
> + if (INTEL_INFO(dev_priv)->gen >= 7)
> + lines = min(lines, 2048);
> +
> + return lines * fb->pitches[0];
> +}
> +
> +static int intel_fbc_setup_cfb(struct intel_crtc *crtc)
> +{
> + struct drm_i915_private *dev_priv = crtc->base.dev->dev_private;
> + struct drm_framebuffer *fb = crtc->base.primary->fb;
> + int size, fb_cpp;
> +
> + size = intel_fbc_calculate_cfb_size(crtc);
> + fb_cpp = drm_format_plane_cpp(fb->pixel_format, 0);

Can we just all it 'cpp' please. We already have too many names for the
same thing. Someone could also do a small search&replace to unify the
whatever we have currently.

> +
> if (size <= dev_priv->fbc.uncompressed_size)
> return 0;
>
> @@ -897,8 +948,7 @@ static void __intel_fbc_update(struct drm_i915_private *dev_priv)
> goto out_disable;
> }
>
> - if (intel_fbc_setup_cfb(dev_priv, obj->base.size,
> - drm_format_plane_cpp(fb->pixel_format, 0))) {
> + if (intel_fbc_setup_cfb(intel_crtc)) {
> set_no_fbc_reason(dev_priv, FBC_STOLEN_TOO_SMALL);
> goto out_disable;
> }
> --
> 2.5.3

--
Ville Syrjälä
Intel OTC