On Wed, Feb 08, 2012 at 01:34:13PM +0000, Chris Wilson wrote: > This is a revert of 6aa56062eaba67adfb247cded244fd877329588d. > > This was originally introduced to workaround reads of the ringbuffer > registers returning 0 on SandyBridge causing hangs due to ringbuffer > overflow. The root cause here was reads through the GT powerwell require > the forcewake dance, something we only learnt of later. Now it appears > that reading the reported head position from the HWS is returning > garbage, leading once again to hangs. > > For example, on q35 the autoreported head reports: > [ 217.975608] head now 00010000, actual 00010000 > [ 436.725613] head now 00200000, actual 00200000 > [ 462.956033] head now 00210000, actual 00210010 > [ 485.501409] head now 00400000, actual 00400020 > [ 508.064280] head now 00410000, actual 00410000 > [ 530.576078] head now 00600000, actual 00600020 > [ 553.273489] head now 00610000, actual 00610018 > which appears reasonably sane. In contrast, if we look at snb: > [ 141.970680] head now 00e10000, actual 00008238 > [ 141.974062] head now 02734000, actual 000083c8 > [ 141.974425] head now 00e10000, actual 00008488 > [ 141.980374] head now 032b5000, actual 000088b8 > [ 141.980885] head now 03271000, actual 00008950 > [ 142.040628] head now 02101000, actual 00008b40 > [ 142.180173] head now 02734000, actual 00009050 > [ 142.181090] head now 00000000, actual 00000ae0 > [ 142.183737] head now 02734000, actual 00009050 > > In addition, the automatic reporting of the head position is scheduled > to be defeatured in the future. It has no more utility, remove it. > > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=45492 > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk> Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch> I'm on the fence whether we should include this in -fixes. On one hand it fixes a severe issue on snb, but introduces a perf regression without the second patch. Otoh we've never shipped snb without it broken like this. But if it turns out that this is broken on ilk and earlier, too, I think we definitely need these two patches in -fixes. -Daniel -- Daniel Vetter Mail: daniel at ffwll.ch Mobile: +41 (0)79 365 57 48
