[PATCH v6 1/6] drm/i915/skl: Add support for the SAGV, fix underrun hangs

Lyude
2016-08-02T22:37:32Z

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 v5:
- Don't use is_power_of_2. Makes things confusing
- Don't use the old state to figure out whether or not to
enable/disable the sagv, use the new one
- Split the loop in skl_disable_sagv into it's own function
- Move skl_sagv_enable/disable() calls into intel_atomic_commit_tail()
Changes since v4:
- Use is_power_of_2 against active_crtcs to check whether we have > 1
pipe enabled
- Fix skl_sagv_get_hw_state(): (temp & 0x1) indicates disabled, 0x0
enabled
- Call skl_sagv_enable/disable() from pre/post-plane updates
Changes since v3:
- Use time_before() to compare timeout to jiffies
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

Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Lyude <cpaul@redhat.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: stable@vger.kernel.org
---
drivers/gpu/drm/i915/i915_drv.h | 2 +
drivers/gpu/drm/i915/i915_reg.h | 5 ++
drivers/gpu/drm/i915/intel_display.c | 11 ++++
drivers/gpu/drm/i915/intel_drv.h | 2 +
drivers/gpu/drm/i915/intel_pm.c | 112 +++++++++++++++++++++++++++++++++++
5 files changed, 132 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 65ada5d..87018d3 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -1962,6 +1962,8 @@ struct drm_i915_private {
struct i915_suspend_saved_registers regfile;
struct vlv_s0ix_state vlv_s0ix_state;

+ bool skl_sagv_enabled;
+
struct {
/*
* Raw watermark latency values:
diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index 2f93d4a..5fb1c63 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -7170,6 +7170,11 @@ enum {
#define HSW_PCODE_DE_WRITE_FREQ_REQ 0x17
#define DISPLAY_IPS_CONTROL 0x19
#define HSW_PCODE_DYNAMIC_DUTY_CYCLE_CONTROL 0x1A
+#define GEN9_PCODE_SAGV_CONTROL 0x21
+#define GEN9_SAGV_DISABLE 0x0
+#define GEN9_SAGV_LOW_FREQ 0x1
+#define GEN9_SAGV_HIGH_FREQ 0x2
+#define GEN9_SAGV_DYNAMIC_FREQ 0x3
#define GEN6_PCODE_DATA _MMIO(0x138128)
#define GEN6_PCODE_FREQ_IA_RATIO_SHIFT 8
#define GEN6_PCODE_FREQ_RING_RATIO_SHIFT 16
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index a8e8cc8..001c885 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -13692,6 +13692,14 @@ static void intel_atomic_commit_tail(struct drm_atomic_state *state)
intel_state->cdclk_pll_vco != dev_priv->cdclk_pll.vco))
dev_priv->display.modeset_commit_cdclk(state);

+ /*
+ * SKL workaround: bspec recommends we disable the SAGV when we
+ * have more then one pipe enabled
+ */
+ if (IS_SKYLAKE(dev_priv) &&
+ hweight32(intel_state->active_crtcs) > 1)
+ skl_disable_sagv(dev_priv);
+
intel_modeset_verify_disabled(dev);
}

@@ -13765,6 +13773,9 @@ static void intel_atomic_commit_tail(struct drm_atomic_state *state)
intel_modeset_verify_crtc(crtc, old_crtc_state, crtc->state);
}

+ if (hweight32(intel_state->active_crtcs) <= 1)
+ skl_enable_sagv(dev_priv);
+
drm_atomic_helper_commit_hw_done(state);

if (intel_state->modeset)
diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index 50cdc89..6b0532a 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -1709,6 +1709,8 @@ void ilk_wm_get_hw_state(struct drm_device *dev);
void skl_wm_get_hw_state(struct drm_device *dev);
void skl_ddb_get_hw_state(struct drm_i915_private *dev_priv,
struct skl_ddb_allocation *ddb /* out */);
+int skl_enable_sagv(struct drm_i915_private *dev_priv);
+int skl_disable_sagv(struct drm_i915_private *dev_priv);
uint32_t ilk_pipe_pixel_rate(const struct intel_crtc_state *pipe_config);
bool ilk_disable_lp_wm(struct drm_device *dev);
int sanitize_rc6_option(struct drm_i915_private *dev_priv, int enable_rc6);
diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index f610b71..68721a5 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -2884,6 +2884,116 @@ skl_wm_plane_id(const struct intel_plane *plane)
}

static void
+skl_sagv_get_hw_state(struct drm_i915_private *dev_priv)
+{
+ u32 temp;
+ int ret;
+
+ if (IS_BROXTON(dev_priv))
+ return;
+
+ mutex_lock(&dev_priv->rps.hw_lock);
+ ret = sandybridge_pcode_read(dev_priv, GEN9_PCODE_SAGV_CONTROL, &temp);
+ mutex_unlock(&dev_priv->rps.hw_lock);
+
+ if (!ret) {
+ dev_priv->skl_sagv_enabled = !(temp & 0x1);
+ } else {
+ /*
+ * If for some reason we can't access the SAGV state, follow
+ * the bspec and assume it's enabled
+ */
+ DRM_ERROR("Failed to get SAGV state, assuming enabled\n");
+ dev_priv->skl_sagv_enabled = true;
+ }
+}
+
+/*
+ * SAGV dynamically adjusts the system agent voltage and clock frequencies
+ * depending on power and performance requirements. The display engine access
+ * to system memory is blocked during the adjustment time. Having this enabled
+ * in multi-pipe configurations can cause issues (such as underruns causing
+ * full system hangs), and the bspec also suggests that software disable it
+ * when more then one pipe is enabled.
+ */
+int
+skl_enable_sagv(struct drm_i915_private *dev_priv)
+{
+ int ret;
+
+ if (IS_BROXTON(dev_priv))
+ return 0;
+ if (dev_priv->skl_sagv_enabled)
+ return 0;
+
+ mutex_lock(&dev_priv->rps.hw_lock);
+ DRM_DEBUG_KMS("Enabling the SAGV\n");
+
+ ret = sandybridge_pcode_write(dev_priv, GEN9_PCODE_SAGV_CONTROL,
+ GEN9_SAGV_DYNAMIC_FREQ);
+ if (!ret)
+ dev_priv->skl_sagv_enabled = true;
+ else
+ DRM_ERROR("Failed to enable the SAGV\n");
+
+ /* We don't need to wait for SAGV when enabling */
+ mutex_unlock(&dev_priv->rps.hw_lock);
+ return ret;
+}
+
+static int
+skl_do_sagv_disable(struct drm_i915_private *dev_priv)
+{
+ int ret;
+ uint32_t temp;
+
+ ret = sandybridge_pcode_write(dev_priv, GEN9_PCODE_SAGV_CONTROL,
+ GEN9_SAGV_DISABLE);
+ if (ret) {
+ DRM_ERROR("Failed to disable the SAGV\n");
+ return ret;
+ }
+
+ ret = sandybridge_pcode_read(dev_priv, GEN9_PCODE_SAGV_CONTROL,
+ &temp);
+ if (ret) {
+ DRM_ERROR("Failed to check the status of the SAGV\n");
+ return ret;
+ }
+
+ return temp & 0x1;
+}
+
+int
+skl_disable_sagv(struct drm_i915_private *dev_priv)
+{
+ int ret, result;
+
+ if (IS_BROXTON(dev_priv))
+ return 0;
+ if (!dev_priv->skl_sagv_enabled)
+ return 0;
+
+ mutex_lock(&dev_priv->rps.hw_lock);
+ DRM_DEBUG_KMS("Disabling the SAGV\n");
+
+ /* bspec says to keep retrying for at least 1 ms */
+ ret = wait_for(result = skl_do_sagv_disable(dev_priv), 1);
+ mutex_unlock(&dev_priv->rps.hw_lock);
+
+ if (ret == -ETIMEDOUT)
+ DRM_ERROR("Request to disable SAGV timed out\n");
+ else {
+ if (result == 1)
+ dev_priv->skl_sagv_enabled = false;
+
+ ret = result;
+ }
+
+ 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 */
@@ -4236,6 +4346,8 @@ 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)