Re: Using cairo with image surface backend results hangs system

On Tue, 13 Nov 2012 09:57:57 +0000
Chris Wilson <[email protected]> wrote:

> On Mon, 12 Nov 2012 14:31:26 -0700, "Carl D. Blake" <[email protected]> wrote:
> > I'm trying to use cairo with a DM8168 based system.  I want to be able
> > to use it with the framebuffer so I've set it up to use the image
> > surface backend.  I've mmaped the framebuffer to a memory location and
> > passed that as the data pointer to cairo_image_surface_create_for_data.
> > It appears to work for a while, but it always hangs the system at some
> > point when any drawing is being done (cairo_show_text or cairo_stroke).
> > I realize that cairo is drawing directly to the framebuffer, but I
> > didn't think this would be a problem.  Am I doing something wrong here?
> 
> It should work, Cairo should not generate out-of-bounds write or reads.
> So I would suggest something is going wrong at the hardware/driver level
> if the machine stops responding.

Based on the symptoms, looks like it could be "Advisory 1.1.38 NEON
Instructions Executed on a Non-Cached Memory-Mapped Address Result in
Lockup" described in
    http://www.ti.com/lit/er/sprz329c/sprz329c.pdf
 
> However, I can not recommend that you use an UC or WC mapping for a
> Cairo surface, except for the final blit. Many of the operators that
> Cairo performs involve a readback from memory, which from a scanout will
> be very slow and may give the appearance of the machine freezing. (The
> usual solution is to use a shadow framebuffer for the composition with a
> blit (CAIRO_OPERATOR_SOURCE) onto the scanout for display.)

-- 
Best regards,
Siarhei Siamashka
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