[Intel-gfx] [PATCH 2/2] drm/i915/bxt: Explicitly clear the Turbo control register

[Chris Wilson]

On Thu, Apr 21, 2016 at 12:33:41PM +0530, akash.goel at intel.com wrote:
> From: Akash Goel <akash.goel at intel.com>
> 
> As a part of WaGsvDisableTurbo, Driver makes an early exit from the
> Gen9 Turbo enabling function, so doesn't program the Turbo Control register.
> But BIOS could leave the Hw Turbo as enabled, so need to explicitly clear
> out the Control register just to avoid inconsitency with debugfs
> interface, which will show Turbo as enabled only and that is not expected
> after adding the WaGsvDisableTurbo. Apart from this there is no problem
> even if the Turbo is left enabled in the Control register, as the Up/Down
> interrupts would remain masked.
> 
> Signed-off-by: Akash Goel <akash.goel at intel.com>
> ---
>  drivers/gpu/drm/i915/intel_pm.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> index b7c2186..41d5586 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -4804,6 +4804,16 @@ static void gen9_enable_rps(struct drm_device *dev)
>  
>  	/* WaGsvDisableTurbo: Workaround to disable turbo on BXT A* */
>  	if (IS_BXT_REVID(dev, 0, BXT_REVID_A1)) {
> +		/*
> +		 * BIOS could leave the Hw Turbo enabled, so need to explicitly
> +		 * clear out the Control register just to avoid inconsitency
> +		 * with debugfs interface, which will show  Turbo as enabled
> +		 * only and that is not expected by the User after adding the
> +		 * WaGsvDisableTurbo. Apart from this there is no problem even
> +		 * if the Turbo is left enabled in the Control register, as the
> +		 * Up/Down interrupts would remain masked.
> +		 */
> +		I915_WRITE(GEN6_RP_CONTROL, 0);

First question. Do we not want to sanitize bios state for everybody
during init? That is the usual procedure.

None of the *_disable_rps() actually clear GEN6_RP_CONTROL. They should
according to the rationale above.  And then this should be a call to
gen9_disable_rps().
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre