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    SubjectRe: [PATCH] drm/i915,agp/intel: Do not clear stolen entries
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    On Sun, 23 Jan 2011 23:40:41 -0800 (PST), Hugh Dickins <hughd@google.com> wrote:
    > It improved matters for me (on a two-year-old Aspire One which had been
    > showing the same few characters of text repeated a large number of times
    > across the screen with 2.6.38-rc1 and rc2): the VESA framebuffer showing
    > good text at last. But crashed once I tried startx, netconsole showing:

    [snip]

    > But your comment above on clear_range was very helpful: your latest
    > patch fixed one call, but left two others unfixed. Please fold in:
    >
    > --- a/drivers/gpu/drm/i915/i915_gem_gtt.c 2011-01-23 11:52:47.350395154 -0800
    > +++ b/drivers/gpu/drm/i915/i915_gem_gtt.c 2011-01-23 20:13:01.457805176 -0800
    > @@ -36,7 +36,7 @@ void i915_gem_restore_gtt_mappings(struc
    >
    > /* First fill with scratch pages */
    > intel_gtt_clear_range(dev_priv->mm.gtt_start / PAGE_SIZE,
    > - dev_priv->mm.gtt_end / PAGE_SIZE);
    > + (dev_priv->mm.gtt_end - dev_priv->mm.gtt_start) / PAGE_SIZE);
    >
    > list_for_each_entry(obj, &dev_priv->mm.gtt_list, gtt_list) {
    > i915_gem_clflush_object(obj);
    > --- a/drivers/gpu/drm/i915/i915_gem.c 2011-01-23 11:52:47.346395154 -0800
    > +++ b/drivers/gpu/drm/i915/i915_gem.c 2011-01-23 20:10:58.081193280 -0800
    > @@ -149,7 +149,7 @@ void i915_gem_do_init(struct drm_device
    > dev_priv->mm.mappable_gtt_total = min(end, mappable_end) - start;
    >
    > /* Take over this portion of the GTT */
    > - intel_gtt_clear_range(start / PAGE_SIZE, end / PAGE_SIZE);
    > + intel_gtt_clear_range(start / PAGE_SIZE, (end - start) / PAGE_SIZE);
    > }

    The patch I finally applied did include those fixes. After making the
    mistake once, I had to double check the other call sites.

    > On this laptop I'm typing from (GM965 with KMS), I've had no trouble
    > getting X up; but when typing in one of the xterms, typed characters
    > often stop echoing, until I shift to a different window, whereupon
    > they appear. This condition cleared (for a while) by switching to
    > VESA fb console and back; no such problem observed on that console.
    >
    > Does that sound familiar? I have no evidence whatever that i915 is
    > to blame here. Several times I tried bisecting last week, but each
    > attempt ended up in a nonsensical place, because the effect does not
    > occur to order. So I'd sometimes mark a bisection point as good when
    > I guess it must actually have been bad. Perhaps it's a matter of
    > timing or an uninitialized variable. But while I'm here, worth asking
    > if that behaviour sounds like anything you might be responsible for?

    Sounds suspiciously like the batch buffer is not being dispatched and
    flushed to the scanout. A very similar bug was recently fixed for
    xf86-video-intel 2.14.0 which was causing deferred output.
    -Chris

    --
    Chris Wilson, Intel Open Source Technology Centre


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