On Fri, Jul 12, 2013 at 06:08:25PM +0100, Chris Wilson wrote: > In theory, the different register blocks were meant to be only ever > touched when holding either the struct_mutex, mode_config.lock or even a > specific localised lock. This does not seem to be the case, and the > hardware reacts extremely badly if we attempt to concurrently access two > registers within the same cacheline. > > v2: Rebase onto uncore > > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=63914 > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk> > --- > drivers/gpu/drm/i915/intel_uncore.c | 9 ++++++--- > 1 file changed, 6 insertions(+), 3 deletions(-) > > diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c > index d7989b8..a89efc6 100644 > --- a/drivers/gpu/drm/i915/intel_uncore.c > +++ b/drivers/gpu/drm/i915/intel_uncore.c > @@ -342,21 +342,21 @@ hsw_unclaimed_reg_check(struct drm_i915_private *dev_priv, u32 reg) > > #define __i915_read(x, y) \ > u##x i915_read##x(struct drm_i915_private *dev_priv, u32 reg, bool trace) { \ > + unsigned long irqflags; \ > u##x val = 0; \ > + spin_lock_irqsave(&dev_priv->uncore.lock, irqflags); \ > if (IS_GEN5(dev_priv->dev)) \ > ilk_dummy_write(dev_priv); \ > if (NEEDS_FORCE_WAKE((dev_priv), (reg))) { \ > - unsigned long irqflags; \ > - spin_lock_irqsave(&dev_priv->uncore.lock, irqflags); \ Looking at this now, it looks like the old code was wrong. I think we needed the lock before ilk_dummy_write when introduced in commit a8b1397d717e36abd9e45f8fee61d800f7d236ec Author: Daniel Vetter <daniel.vetter at ffwll.ch> Date: Thu Oct 18 14:16:09 2012 +0200 drm/i915: implement WaIssueDummyWriteToWakeupFromRC6 While on this topic, did we really need a dummy write or a write, that seems very weird. That also has a bug where we don't issue the dummy write before doing a read of the fifo free entries. Anyway, it seems we had no bugs associated with it, so meh. I also think it might be time for per gen MMIO functions, but don't care enough to do anything more than state it. > if (dev_priv->uncore.forcewake_count == 0) \ > dev_priv->uncore.funcs.force_wake_get(dev_priv); \ > val = read##y(dev_priv->regs + reg); \ > if (dev_priv->uncore.forcewake_count == 0) \ > dev_priv->uncore.funcs.force_wake_put(dev_priv); \ > - spin_unlock_irqrestore(&dev_priv->uncore.lock, irqflags); \ > } else { \ > val = read##y(dev_priv->regs + reg); \ > } \ > + spin_unlock_irqrestore(&dev_priv->uncore.lock, irqflags); \ > if (trace) trace_i915_reg_rw(false, reg, val, sizeof(val)); \ > return val; \ > } > @@ -369,8 +369,10 @@ __i915_read(64, q) > > #define __i915_write(x, y) \ > void i915_write##x(struct drm_i915_private *dev_priv, u32 reg, u##x val, bool trace) { \ > + unsigned long irqflags; \ > u32 __fifo_ret = 0; \ > if (trace) trace_i915_reg_rw(true, reg, val, sizeof(val)); \ > + spin_lock_irqsave(&dev_priv->uncore.lock, irqflags); \ > if (NEEDS_FORCE_WAKE((dev_priv), (reg))) { \ > __fifo_ret = __gen6_gt_wait_for_fifo(dev_priv); \ > } \ I think for the sake of timing, doing the trace after the lock is more desirable. > @@ -382,6 +384,7 @@ void i915_write##x(struct drm_i915_private *dev_priv, u32 reg, u##x val, bool tr > gen6_gt_check_fifodbg(dev_priv); \ > } \ > hsw_unclaimed_reg_check(dev_priv, reg); \ > + spin_unlock_irqrestore(&dev_priv->uncore.lock, irqflags); \ > } > __i915_write(8, b) > __i915_write(16, w) Is there any reason you kept read##y instead of using the new raw functions? I would like to have only one place where we readl/writel if possible. Anyway, I can't find anything wrong with the patch otherwise, and I think we can try throwing it at all hangs from SNB->HSW since it should serialize the display accesses too. So let's say with all my comments at least read by someone, it's Reviewed-by: Ben Widawsky <ben at bwidawsk.net> -- Ben Widawsky, Intel Open Source Technology Center
