Re: [PATCH 2/2] drm/i915: fix D_COMP usage on BDW

[Damien Lespiau <damien.lespiau@intel.com>]

On Fri, Jul 04, 2014 at 11:59:58AM -0300, Paulo Zanoni wrote:
> From: Paulo Zanoni <paulo.r.zanoni@intel.com>
> 
> On HSW, the D_COMP register can be accessed through the mailbox (read
> and write) or through MMIO on a MCHBAR offset (read only). On BDW, the
> access should be done through MMIO on another address. So to account
> for all these cases, create hsw_read_dcomp() with the correct
> implementation for reading, and also fix hsw_write_dcomp() to do the
> correct thing on BDW.
> 
> With this patch, we can now get back from the PC8+ state on BDW. We
> were previously getting a black screen and lots of dmesg errors.
> Please notice that the bug only happens when you actually reach the
> PC8+ states, not when you only allow it.
> 
> Testcase: igt/pm_rpm/rte
> Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>

Reviewed-by: Damien Lespiau <damien.lespiau@intel.com>

-- 
Damien

> ---
>  drivers/gpu/drm/i915/i915_reg.h      |  5 ++++-
>  drivers/gpu/drm/i915/intel_display.c | 21 ++++++++++++++++-----
>  2 files changed, 20 insertions(+), 6 deletions(-)
> 
> I tested this before my BDW machine died and it worked. I couldn't test it again
> since then. Please notice that this is an important patch that prevents the
> machine from being useless after runtime PM is enabled (and we actually reach
> package C8 or deeper states). This will be even easier to reproduce after we
> merge Daniel's "RPM on DPMS" series.
> 
> diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
> index 3488567..3e4b13e 100644
> --- a/drivers/gpu/drm/i915/i915_reg.h
> +++ b/drivers/gpu/drm/i915/i915_reg.h
> @@ -5962,7 +5962,10 @@ enum punit_power_well {
>  #define  LCPLL_CD_SOURCE_FCLK		(1<<21)
>  #define  LCPLL_CD_SOURCE_FCLK_DONE	(1<<19)
>  
> -#define D_COMP				(MCHBAR_MIRROR_BASE_SNB + 0x5F0C)
> +/* Please see hsw_read_dcomp() and hsw_write_dcomp() before using this register,
> + * since on HSW we can't write to it using I915_WRITE. */
> +#define D_COMP_HSW			(MCHBAR_MIRROR_BASE_SNB + 0x5F0C)
> +#define D_COMP_BDW			0x138144
>  #define  D_COMP_RCOMP_IN_PROGRESS	(1<<9)
>  #define  D_COMP_COMP_FORCE		(1<<8)
>  #define  D_COMP_COMP_DISABLE		(1<<0)
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 6986594..3a8c9a7 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -7362,6 +7362,16 @@ static void assert_can_disable_lcpll(struct drm_i915_private *dev_priv)
>  	WARN(!dev_priv->pm.irqs_disabled, "IRQs enabled\n");
>  }
>  
> +static uint32_t hsw_read_dcomp(struct drm_i915_private *dev_priv)
> +{
> +	struct drm_device *dev = dev_priv->dev;
> +
> +	if (IS_HASWELL(dev))
> +		return I915_READ(D_COMP_HSW);
> +	else
> +		return I915_READ(D_COMP_BDW);
> +}
> +
>  static void hsw_write_dcomp(struct drm_i915_private *dev_priv, uint32_t val)
>  {
>  	struct drm_device *dev = dev_priv->dev;
> @@ -7373,9 +7383,9 @@ static void hsw_write_dcomp(struct drm_i915_private *dev_priv, uint32_t val)
>  			DRM_ERROR("Failed to write D_COMP\n");
>  		mutex_unlock(&dev_priv->rps.hw_lock);
>  	} else {
> -		I915_WRITE(D_COMP, val);
> +		I915_WRITE(D_COMP_BDW, val);
> +		POSTING_READ(D_COMP_BDW);
>  	}
> -	POSTING_READ(D_COMP);
>  }
>  
>  /*
> @@ -7413,12 +7423,13 @@ static void hsw_disable_lcpll(struct drm_i915_private *dev_priv,
>  	if (wait_for((I915_READ(LCPLL_CTL) & LCPLL_PLL_LOCK) == 0, 1))
>  		DRM_ERROR("LCPLL still locked\n");
>  
> -	val = I915_READ(D_COMP);
> +	val = hsw_read_dcomp(dev_priv);
>  	val |= D_COMP_COMP_DISABLE;
>  	hsw_write_dcomp(dev_priv, val);
>  	ndelay(100);
>  
> -	if (wait_for((I915_READ(D_COMP) & D_COMP_RCOMP_IN_PROGRESS) == 0, 1))
> +	if (wait_for((hsw_read_dcomp(dev_priv) & D_COMP_RCOMP_IN_PROGRESS) == 0,
> +		     1))
>  		DRM_ERROR("D_COMP RCOMP still in progress\n");
>  
>  	if (allow_power_down) {
> @@ -7467,7 +7478,7 @@ static void hsw_restore_lcpll(struct drm_i915_private *dev_priv)
>  		POSTING_READ(LCPLL_CTL);
>  	}
>  
> -	val = I915_READ(D_COMP);
> +	val = hsw_read_dcomp(dev_priv);
>  	val |= D_COMP_COMP_FORCE;
>  	val &= ~D_COMP_COMP_DISABLE;
>  	hsw_write_dcomp(dev_priv, val);
> -- 
> 2.0.0
> 
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