Re: [PATCH 4/4] drm/i915: Preserve the state of power wells not explicitly enabled

[Ander Conselvan De Oliveira <conselvan2@gmail.com>]

On Wed, 2017-02-15 at 13:59 +0200, Imre Deak wrote:
> Atm, power wells that BIOS has enabled, but which we don't explicitly
> enable during power domain initialization would get disabled as we clear
> the BIOS request bit in the given power well sync_hw hook. To prevent
> this copy over any set request bits in the BIOS request register to the
> driver request register and clear the BIOS request bit only afterwards.
> 
> This doesn't make a difference now, since we enable all power wells
> during power domain initialization. A follow-up patchset will add power
> wells for which this isn't true, so fix up the inconsistency.
> 
> Cc: Ander Conselvan de Oliveira <conselvan2@gmail.com>
> Cc: David Weinehall <david.weinehall@linux.intel.com>
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Signed-off-by: Imre Deak <imre.deak@intel.com>
> ---
>  drivers/gpu/drm/i915/intel_runtime_pm.c | 18 ++++++++++++------
>  1 file changed, 12 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_runtime_pm.c b/drivers/gpu/drm/i915/intel_runtime_pm.c
> index b7b0e0f..e747215 100644
> --- a/drivers/gpu/drm/i915/intel_runtime_pm.c
> +++ b/drivers/gpu/drm/i915/intel_runtime_pm.c
> @@ -855,12 +855,14 @@ static void skl_set_power_well(struct drm_i915_private *dev_priv,
>  static void hsw_power_well_sync_hw(struct drm_i915_private *dev_priv,
>  				   struct i915_power_well *power_well)
>  {
> -	/*
> -	 * We're taking over the BIOS, so clear any requests made by it since
> -	 * the driver is in charge now.
> -	 */
> -	if (I915_READ(HSW_PWR_WELL_BIOS) & HSW_PWR_WELL_ENABLE_REQUEST)
> +	/* Take over the request bit if set by BIOS. */
> +	if (I915_READ(HSW_PWR_WELL_BIOS) & HSW_PWR_WELL_ENABLE_REQUEST) {
> +		if (!(I915_READ(HSW_PWR_WELL_DRIVER) &
> +		      HSW_PWR_WELL_ENABLE_REQUEST))
> +			I915_WRITE(HSW_PWR_WELL_DRIVER,
> +				   HSW_PWR_WELL_ENABLE_REQUEST);
>  		I915_WRITE(HSW_PWR_WELL_BIOS, 0);
> +	}
>  }
>  
>  static void hsw_power_well_enable(struct drm_i915_private *dev_priv,
> @@ -890,8 +892,12 @@ static void skl_power_well_sync_hw(struct drm_i915_private *dev_priv,
>  	uint32_t mask = SKL_POWER_WELL_REQ(power_well->id);
>  	uint32_t bios_req = I915_READ(HSW_PWR_WELL_BIOS);
>  
> -	/* Clear any request made by BIOS as driver is taking over */
> +	/* Take over the request bit if set by BIOS. */
>  	if (bios_req & mask) {
> +		uint32_t drv_req = I915_READ(HSW_PWR_WELL_DRIVER);
> +
> +		if (!(drv_req & mask))
> +			I915_WRITE(HSW_PWR_WELL_DRIVER, drv_req | mask);
>  		I915_WRITE(HSW_PWR_WELL_BIOS, bios_req & ~mask);
>  	}
>  }

With this change it will be possible for the hardware state readout code to
inherit the state of the DDI IO power wells in Geminilake, which is what I
wanted. I'm just thinking if there is a risk for inconsistency if the hardware
state readout doesn't fix the reference count to a domain that is left enabled.
Would it make sense to add a WARN or at least a debug message somewhere if this
happens, so it doesn't go unnoticed?

Ander

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