Re: [PATCH 12/12] drm/i915: Disable DDR DVFS on CHV

Jesse Barnes
2015-03-06T17:31:59Z

On 03/05/2015 11:19 AM, ville.syrjala@linux.intel.com wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
>
> DDR DVFS introduces massive memory latencies which can't be handled by
> the PND deadline stuff. Instead the watermarks will need to be
> programmed to compensate for the latency and the deadlines will need to
> be programmed to tight fixed values. That means DDR DVFS can only be
> enabled if the display FIFOs are large enough, and that pretty much
> means we have to manually repartition them to suit the needs of the
> moment.
>
> That's a lot of change, so in the meantime let's just disable DDR DVFS
> to get the display(s) to be stable.
>
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> ---
> drivers/gpu/drm/i915/i915_reg.h | 5 +++++
> drivers/gpu/drm/i915/intel_pm.c | 34 ++++++++++++++++++++++++++++++++++
> 2 files changed, 39 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
> index 5a20f58..744d162 100644
> --- a/drivers/gpu/drm/i915/i915_reg.h
> +++ b/drivers/gpu/drm/i915/i915_reg.h
> @@ -630,6 +630,11 @@ enum skl_disp_power_wells {
> #define FB_GFX_FMIN_AT_VMIN_FUSE 0x137
> #define FB_GFX_FMIN_AT_VMIN_FUSE_SHIFT 8
>
> +#define PUNIT_REG_DDR_SETUP2 0x139
> +#define FORCE_DDR_FREQ_REQ_ACK (1 << 8)
> +#define FORCE_DDR_LOW_FREQ (1 << 1)
> +#define FORCE_DDR_HIGH_FREQ (1 << 0)
> +
> #define PUNIT_GPU_STATUS_REG 0xdb
> #define PUNIT_GPU_STATUS_MAX_FREQ_SHIFT 16
> #define PUNIT_GPU_STATUS_MAX_FREQ_MASK 0xff
> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> index 1dd82ec..fc03e24 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -235,6 +235,28 @@ static const struct cxsr_latency *intel_get_cxsr_latency(int is_desktop,
> return NULL;
> }
>
> +static void chv_set_memory_dvfs(struct drm_i915_private *dev_priv, bool enable)
> +{
> + u32 val;
> +
> + mutex_lock(&dev_priv->rps.hw_lock);
> +
> + val = vlv_punit_read(dev_priv, PUNIT_REG_DDR_SETUP2);
> + if (enable)
> + val &= ~FORCE_DDR_HIGH_FREQ;
> + else
> + val |= FORCE_DDR_HIGH_FREQ;
> + val &= ~FORCE_DDR_LOW_FREQ;
> + val |= FORCE_DDR_FREQ_REQ_ACK;
> + vlv_punit_write(dev_priv, PUNIT_REG_DDR_SETUP2, val);
> +
> + if (wait_for((vlv_punit_read(dev_priv, PUNIT_REG_DDR_SETUP2) &
> + FORCE_DDR_FREQ_REQ_ACK) == 0, 3))
> + DRM_ERROR("timed out waiting for Punit DDR DVFS request\n");
> +
> + mutex_unlock(&dev_priv->rps.hw_lock);
> +}
> +
> static void chv_set_memory_pm5(struct drm_i915_private *dev_priv, bool enable)
> {
> u32 val;
> @@ -282,6 +304,7 @@ void intel_set_memory_cxsr(struct drm_i915_private *dev_priv, bool enable)
> enable ? "enabled" : "disabled");
> }
>
> +
> /*
> * Latency for FIFO fetches is dependent on several factors:
> * - memory configuration (speed, channels)
> @@ -992,6 +1015,17 @@ static void valleyview_update_wm(struct drm_crtc *crtc)
> wm.pipe[pipe].primary, wm.pipe[pipe].cursor,
> wm.sr.plane, wm.sr.cursor);
>
> + /*
> + * FIXME DDR DVFS introduces massive memory latencies which
> + * are not known to system agent so any deadline specified
> + * by the display may not be respected. To support DDR DVFS
> + * the watermark code needs to be rewritten to essentially
> + * bypass deadline mechanism and rely solely on the
> + * watermarks. For now disable DDR DVFS.
> + */
> + if (IS_CHERRYVIEW(dev_priv))
> + chv_set_memory_dvfs(dev_priv, false);
> +
> if (!cxsr_enabled)
> intel_set_memory_cxsr(dev_priv, false);
>
>

Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>