Re: [v5,1/6] drm/i915/skl: Add support for the SAGV, fix underrun hangs

Hans de Goede
2016-08-02T19:51:48Z

Hi,

On 08/02/2016 08:52 PM, cpaul@redhat.com 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 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
> 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 | 12 ++++
> drivers/gpu/drm/i915/intel_drv.h | 2 +
> drivers/gpu/drm/i915/intel_pm.c | 112 +++++++++++++++++++++++++++++++++++
> 5 files changed, 133 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..76ba79f 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -4565,6 +4565,7 @@ static void intel_post_plane_update(struct intel_crtc_state *old_crtc_state)
> struct intel_crtc_state *pipe_config =
> to_intel_crtc_state(crtc->base.state);
> struct drm_device *dev = crtc->base.dev;
> + struct drm_i915_private *dev_priv = to_i915(dev);
> struct drm_plane *primary = crtc->base.primary;
> struct drm_plane_state *old_pri_state =
> drm_atomic_get_existing_plane_state(old_state, primary);
> @@ -4589,6 +4590,9 @@ static void intel_post_plane_update(struct intel_crtc_state *old_crtc_state)
> !old_primary_state->visible))
> intel_post_enable_primary(&crtc->base);
> }
> +
> + if (hweight32(dev_priv->active_crtcs) <= 1)
> + skl_enable_sagv(dev_priv);
> }
>
> static void intel_pre_plane_update(struct intel_crtc_state *old_crtc_state)
> @@ -4649,6 +4653,14 @@ static void intel_pre_plane_update(struct intel_crtc_state *old_crtc_state)
> }
>
> /*
> + * SKL workaround: bspec recommends we disable the SAGV when we have
> + * more then one pipe enabled
> + */
> + if (pipe_config->base.active &&
> + hweight32(dev_priv->active_crtcs | drm_crtc_mask(&crtc->base)) > 1)
> + skl_disable_sagv(dev_priv);
> +
> + /*

Why | drm_crtc_mask? Also if it is a mask I would expect & not | >
Last why are you using drm_crtc_mask here and not in post_plane_update ?

Regards,

Hans

> * If we're doing a modeset, we're done. No need to do any pre-vblank
> * watermark programming here.
> */
> 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)
>