[Bug 61182] r600g causes KWin crashes with kernel 3.8

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=61182

--- Comment #40 from D. Hugh Redelmeier <hugh at mimosa.com> ---
Thanks, Neils, for the patch in comment #38.

Warning: the following comments are made with no understanding of X code.

"writting" should be "writing"

What is 0x000fffff?  I would find the code clearer if this constant were given
a name (RADEON_MAX_DMA?).

Why code
  nfill = (size / 0x000fffff) + !!(size % 0x000fffff);
instead of the generally more efficient
  nfill = (size+ 0x000fffff - 1) / 0x000fffff;
My guess: to avoid overflow.  But if that is the case, then nfill should be
uint64_t (like size), not just unsigned (which might be only 32 bits).  Any
case where the second statement might have an overflow problem would also be a
problem with nfill being only unsigned 32.

If you know size is not 0, this is even better:
  nfill = ((size - 1) / 0x000fffff) + 1;
If size can be 0, it is probably worth an early-out test to avoid bothering the
GPU anyway:
  if (size == 0) return 0;

I find code is easier to read if the scope of a variable is minimized.  So I'd
make the assignment to fsize also its declaration.

Have you created a patch to get these functions called in place of the
currently broken code?

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