http://bugs.freedesktop.org/show_bug.cgi?id=24837
Summary: Broken ring info in debugfs
Product: DRI
Version: unspecified
Platform: Other
OS/Version: All
Status: NEW
Severity: normal
Priority: medium
Component: DRM/Radeon
AssignedTo: dri-devel@lists.sourceforge.net
ReportedBy: zaj...@gmail.com
First I reported bug #24781 but that was invalid report, there was not bug in
code where I thought.
However there are for sure some issues in current ring info debugfs.
**********
1) We count buffer's elements in following way:
r600.c::r600_debugfs_cp_ring_info
count = (rdp + rdev->cp.ring_size - wdp) & rdev->cp.ptr_mask;
a) We don't divide cp.ring_size by 4 but fortunately this doesn't cause
problems as we use bit multiplication by mask. However maybe we should do so
for code readability?
b) What we count is actually amount of *free* dwords in buffer. This is the
same what gets done in radeon_ring_free_size. You can see results of this
mistake in bug #24535 comment #6 - amount of free and used dwords is the same
which is incorrect. The only exception when this work is empty ring situation.
In radeon_ring.c::radeon_ring_free_size we treat 0 as (rdev->cp.ring_size / 4)
so we get nice (correct):
> 262128 free dwords in ring
> 0 dwords in ring
then.
Ideally this probably should be:
count = (wdp + rdev->cp.ring_size - rdp) & rdev->cp.ptr_mask;
**********
2) We have inconsistent in reading CP_RB_WPTR and CP_RB_RPTR. This leads to
situations like:
> 262127 free dwords in ring
> 0 dwords in ring
where 262127 + 0 != 262144 (and 262144 is buffer size ofc).
That happens because we call radeon_ring_free_size where we calculate amount of
free dwords using rdev->cp.rptr and rdev->cp.wptr. Then we read CP_RB_RPTR and
CP_RB_WPTR and calculate used dwords. As ring changes often this causes
mentioned inconsistency.
I belive we should use rdev->cp.rptr and rdev->cp.wptr in
r600_debugfs_cp_ring_info and eventually consider updating rdev->cp.wptr in
radeon_ring_free_size.
**********
3) Finally we don't detect ring end in printing ring's content in
r600_debugfs_cp_ring_info.
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