On Wed, 25 Apr 2012 21:26:50 +0200, Daniel Vetter <daniel at ffwll.ch> wrote: > On Wed, Apr 25, 2012 at 06:14:37PM +0100, Chris Wilson wrote: > > On Fri, 20 Apr 2012 21:03:35 +0200, Daniel Vetter <daniel.vetter at ffwll.ch> wrote: > > > If we try to do that and the scanlines just wouldn't advance, we > > > busy-hang the machine holding the modeset mutex. Not great for > > > debugging. > > > > > > References: https://bugzilla.kernel.org/show_bug.cgi?id=43020 > > > Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch> > > > > Reviewer hangs head in shame: > > > > > + if (wait_for(I915_READ(pipe_dsl_reg) >= vactive, 1000)) > > > + DRM_ERROR("timed out waiting for vactive in " > > > + "load_detect, scanline: %u\n", > > > + I915_READ(pipe_dsl_reg)); > > > + if (wait_for((dsl = I915_READ(pipe_dsl_reg)) <= vsample, 1000)) > > > + DRM_ERROR("timed out waiting for vsample in " > > > + "load_detect, scanline: %u\n", > > > + I915_READ(pipe_dsl_reg)); > > > > wait_for() catches us out everytime we convert and existing while(), > > because the predicate is when it stops. Perhaps if we had a wait_until, > > but anyway the fix here is: > > > > if (wait_for(I915_READ(pipe_dsl_reg) < vactive, 1000)) > > ... > > if (wait_for((dsl = I915_READ(pipe_dsl_reg)) > vsample, 1000)) > > ... > dinq rectified, it never happened. Thanks for catching this. wait_for() has even more subtleties in store for us, the unwary coder. By default, it uses a 1ms sleep between polling the register, chosen to be kind whilst waiting for panel bits to power up which do take a fair amount of time. Here, that extra delay causes us to sample the vsync rather than the border. The quirk of the [vh]sync is that the monitor bit of ST00 is always true. And since we always seem to pick that row to read we always think there is a CRT present. The choice is either to use the busy-polling variant, wait_for_atomic, or restructure the entire block to use a single timeout with direct reads. And whilst you are modifying the code, convert the polling reads to I915_READ_NOTRACE(). -Chris -- Chris Wilson, Intel Open Source Technology Centre
