Re: Patches for i830 flicker on panning

Daniel Vetter
2013-11-05T07:06:47Z

On Tue, Nov 05, 2013 at 12:20:58AM +0100, Thomas Richter wrote:
> Hi Daniel, dear intel experts,
>
> the following is a "solution" for the flicker on i830 panning. To
> remind you, when panning is enabled on an i830,
> the display shows an annoying 30Hz flicker on some "forbidden"
> positions. On such positions, half of the frames
> is black, and the other half shows a screen that is "ripped in
> half", with one half scrolled to the wrong
> position, and the other half displayed correctly, with a
> discontinuity in the middle.
> That is, every other frame is black, and the ones that are not black
> are "wrong".
>
> The patch is, arguably, ugly as hell, and creates a certain
> "yerkiness", though it does its job. One of the side
> effects this flicker causes is complete crashes and lockups with
> video overlays which are avoided by the patch.
> That is, if you play a video with xine, and then pan over a
> forbidden position, the machine crashes and comes
> to a complete stop.
>
> Sorry if the patch format isn't quite right, and the patch is not
> quite in a final state (not yet fully tested on all possible
> combinations of panning dimensions and display depths), but it's a
> start and "works good enough for me".

Patch is pretty badly whitespace mangled please format it according to
Documentation/SubmittingPatches (git format-patch preferred). Also I think
we should conditionalize this on i830M only, I don't see any other
reports.

One thing to try out still: Does this still work if you tell the ddx to
use a linear frontbuffer?
-Daniel

>
> For that, patch: i9xx_update_plane(...) in intel_display.c,
>
> if (INTEL_INFO(dev)->gen >= 4) {
> I915_MODIFY_DISPBASE(DSPSURF(plane),
> i915_gem_obj_ggtt_offset(obj) +
> intel_crtc->dspaddr_offset);
> I915_WRITE(DSPTILEOFF(plane), (y << 16) | x);
> I915_WRITE(DSPLINOFF(plane), linear_offset);
> + } else if (INTEL_INFO(dev)->gen == 2) {
> + int xflick = (x >> 4) & 0x03;
> + if (xflick == 3) { /* in forbidden column, probably a
> i830 bug */
> + int xfix = 16 + (x & ~(0x3f));
> + int fix_offset = y * fb->pitches[0] + xfix *
> (fb->bits_per_pixel / 8);
> + I915_WRITE(DSPADDR(plane), i915_gem_obj_ggtt_offset(obj) +
> fix_offset);
> + POSTING_READ(reg);
> + intel_wait_for_vblank(dev, intel_crtc->pipe);
> + }
> + I915_WRITE(DSPADDR(plane), i915_gem_obj_ggtt_offset(obj) +
> linear_offset);
> } else
> I915_WRITE(DSPADDR(plane), i915_gem_obj_ggtt_offset(obj) +
> linear_offset);
> POSTING_READ(reg);
>
> The trick is, as you see, first to display the one frame the display
> scrolled off *before* the forbidden column, and
> then scroll to the right position, going to the right. )-:
>
> *Why* that works is unclear to me. Don't ask, just observation.
>
> An improvement would be to check whether the x position did change,
> and if it did not, just avoid all the hack to
> allow smooth vertical scrolling. Still to be done. Maybe later the
> week if the above also works on the R31
> (affected by the same problem).
>
> Greetings,
> Thomas
>

--
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch