On 01/03/2012 03:27 PM, Alex Deucher wrote:
On Mon, Jan 2, 2012 at 5:07 PM, Helge Deller<del...@gmx.de> wrote:
I'm facing the problem with the radeon drm driver, that I now manually need
to set the kernel module parameter radeon.no_wb to 1 at bootup, else X just
hangs in average up to 8 seconds per minute without any real activity (X or
the video driver just seems to wait for something..).
Fedora 13 (kernel 2.6.34.9-69.fc13.x86_64) worked without problems, while
all following Fedora distributions including F16 have this problem.
I'm using a dual-DVI ATI RV280 [FireMV 2200 PCI].
I did compared the sources of those kernels and the only obvious change to
me is in radeon_ring.c: radeon_ring_free_size() where those lines were added
at the top of the function:
if (rdev->wb.enabled)
rdev->cp.rptr =
le32_to_cpu(rdev->wb.wb[RADEON_WB_CP_RPTR_OFFSET/4]);
Given the problems I'm seeing (X-Windows hangs for a few seconds every time)
this fits with the idea, that the driver is waiting for a free slot but
can't find any (maybe due to wrong values returned by not-working WB?).
I'm wondering, if "rdev->wb.enabled" is correct in this place and if
"dev_priv->writeback_works" shouldn't be used instead here?
It's possible that writeback doesn't work on your system in which case
no_wb=1 is apprioriate. dev_priv->writeback_works is part of the old
UMS drm and is not used by KMS. The KMS code does not test if
writeback works prior to enabling it like UMS did. The slow down you
are seeing is caused by the driver waiting for the fence to be written
back to memory. If writeback does not work, the fence is never
written by the hw and the driver has to wait for the fence to time
out.
Alex, thanks for the explanations.
In my opinion this is a regression then. The old code worked without problems,
while with the new driver (or only because of the added code lines) the driver
doesn't work out of the box.
Wouldn't it be an idea to port over the old UMS writeback-check-test to the new
KMS code base to avoid the issues I'm seeing?
I would be willing to test such code or even provide an initial patch if
necessary.
Helge
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