http://bugs.freedesktop.org/show_bug.cgi?id=24781
Summary: Incorrect calculation of free dwords in ring buffer
Product: DRI
Version: XOrg CVS
Platform: Other
OS/Version: All
Status: NEW
Severity: normal
Priority: medium
Component: DRM/Radeon
AssignedTo: [email protected]
ReportedBy: [email protected]
Created an attachment (id=30782)
--> (http://bugs.freedesktop.org/attachment.cgi?id=30782)
drm/radeon/kms: fix calculation of free dwords in ring
There are two scenarios of read/write pointers relation:
1) read lower than write
/----------------------------\
| A B C D E F G |
| 1 2 3 4 5 6 7 8 9 10 11 12 |
\----------------------------/
R W
used = w - r
free = size - used
free = size - (w - r)
free = size - w + r
free = r + size - w
2) write lower than read
/----------------------------\
| E F G A B C D |
| 1 2 3 4 5 6 7 8 9 10 11 12 |
\----------------------------/
W R
free = r - w
I made there ascii pictures to make it clear, as noone believed me today on IRC
we have some bug there ;)
Problem is we calculate free dwords for first situation only (always). We have
to detect second situation and use other calculation then.
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