On Tue, Jul 12, 2016 at 11:21:39AM -0700, Matt Roper wrote: > On Tue, Jul 12, 2016 at 01:36:03PM -0400, Lyude wrote: > > Since the watermark calculations for Skylake are still broken, we're apt > > to hitting underruns very easily under multi-monitor configurations. > > While it would be lovely if this was fixed, it's not. Another problem > > that's been coming from this however, is the mysterious issue of > > underruns causing full system hangs. An easy way to reproduce this with > > a skylake system: > > > > - Get a laptop with a skylake GPU, and hook up two external monitors to > > it > > - Move the cursor from the built-in LCD to one of the external displays > > as quickly as you can > > - You'll get a few pipe underruns, and eventually the entire system will > > just freeze. > > > > After doing a lot of investigation and reading through the bspec, I > > found the existence of the SAGV, which is responsible for adjusting the > > system agent voltage and clock frequencies depending on how much power > > we need. According to the bspec: > > > > "The display engine access to system memory is blocked during the > > adjustment time. SAGV defaults to enabled. Software must use the > > GT-driver pcode mailbox to disable SAGV when the display engine is not > > able to tolerate the blocking time." > > > > The rest of the bspec goes on to explain that software can simply leave > > the SAGV enabled, and disable it when we use interlaced pipes/have more > > then one pipe active. > > > > Sure enough, with this patchset the system hangs resulting from pipe > > underruns on Skylake have completely vanished on my T460s. Additionally, > > the bspec mentions turning off the SAGV with more then one pipe enabled > > as a workaround for display underruns. While this patch doesn't entirely > > fix that, it looks like it does improve the situation a little bit so > > it's likely this is going to be required to make watermarks on Skylake > > fully functional. > > > > Changes since v2: > > - Really apply minor style nitpicks to patch this time > > Changes since v1: > > - Added comments about this probably being one of the requirements to > > fixing Skylake's watermark issues > > - Minor style nitpicks from Matt Roper > > - Disable these functions on Broxton, since it doesn't have an SAGV > > > > Cc: Matt Roper <matthew.d.roper@xxxxxxxxx> > > Cc: Daniel Vetter <daniel.vetter@xxxxxxxx> > > Cc: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx> > > Signed-off-by: Lyude <cpaul@xxxxxxxxxx> > > I don't have a SKL to try this out on (only BXT here), but this matches > my interpretation of the current bspec text, so > > Reviewed-by: Matt Roper <matthew.d.roper@xxxxxxxxx> > > I think this also applies to > > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=94625 > > And maybe a +cc stable? > Oops, one more minor issue below that I missed the first time around. ... > > + /* bspec says to keep retrying for at least 1 ms */ > > + timeout = jiffies + msecs_to_jiffies(1); > > + do { > > + ret = sandybridge_pcode_write(dev_priv, GEN9_PCODE_SAGV_CONTROL, > > + GEN9_SAGV_DISABLE); > > + if (ret) { > > + DRM_ERROR("Failed to disable the SAGV\n"); > > + goto out; > > + } > > + > > + ret = sandybridge_pcode_read(dev_priv, GEN9_PCODE_SAGV_CONTROL, > > + &temp); > > + if (ret) { > > + DRM_ERROR("Failed to check the status of the SAGV\n"); > > + goto out; > > + } > > + } while (!(temp & 0x1) && jiffies < timeout); We shouldn't compare jiffies directly here due to wraparound; you can use time_before() to handle that safely. Matt > > + > > + if (temp & 0x1) { > > + dev_priv->skl_sagv_enabled = false; > > + } else { > > + ret = -1; > > + DRM_ERROR("Request to disable SAGV timed out\n"); > > + } > > + > > +out: > > + mutex_unlock(&dev_priv->rps.hw_lock); > > + return ret; > > +} > > + > > +static void > > skl_ddb_get_pipe_allocation_limits(struct drm_device *dev, > > const struct intel_crtc_state *cstate, > > struct skl_ddb_entry *alloc, /* out */ > > @@ -3686,6 +3789,11 @@ static void skl_write_wm_values(struct drm_i915_private *dev_priv, > > struct drm_device *dev = &dev_priv->drm; > > struct intel_crtc *crtc; > > > > + if (dev_priv->active_crtcs == 1) > > + skl_enable_sagv(dev_priv); > > + else > > + skl_disable_sagv(dev_priv); > > + > > for_each_intel_crtc(dev, crtc) { > > int i, level, max_level = ilk_wm_max_level(dev); > > enum pipe pipe = crtc->pipe; > > @@ -4228,6 +4336,8 @@ void skl_wm_get_hw_state(struct drm_device *dev) > > /* Easy/common case; just sanitize DDB now if everything off */ > > memset(ddb, 0, sizeof(*ddb)); > > } > > + > > + skl_sagv_get_hw_state(dev_priv); > > } > > > > static void ilk_pipe_wm_get_hw_state(struct drm_crtc *crtc) > > -- > > 2.7.4 > > > > -- > Matt Roper > Graphics Software Engineer > IoTG Platform Enabling & Development > Intel Corporation > (916) 356-2795 > _______________________________________________ > Intel-gfx mailing list > Intel-gfx@xxxxxxxxxxxxxxxxxxxxx > https://lists.freedesktop.org/mailman/listinfo/intel-gfx -- Matt Roper Graphics Software Engineer IoTG Platform Enabling & Development Intel Corporation (916) 356-2795 _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
