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

[Arun R Murthy <arun.r.murthy@intel.com>]

On Friday 06 March 2015 12:49 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>
> ---

Since this patch disabled DDR DVFS in the driver, can this be done
once. Here I assume that DDR DVFS gets disabled on each update
watermark call.
Moreover enabling DDR DVFS should be followed with updating
watermarks and display arbiter.

Thanks and Regards,
Arun R Murthy
-------------------
>   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);
>   

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