[Intel-gfx] [PATCH 2/3] drm/i915: Workaround to bump rc6 voltage to 450

[Jesse Barnes]

On Wed, 26 Sep 2012 10:34:01 -0700
Ben Widawsky <ben at bwidawsk.net> wrote:

> BIOS should be setting the minimum voltage for rc6 to be 450mV. Old or
> buggy BIOSen may not be doing this, so we correct it for them. Ideally
> customers should update the BIOS as only it would know the optimal
> values for the platform, so we leave that fact as a DRM_ERROR for the
> user to see.
> 
> Unfortunately this isn't fixing any of the issues it was targeted to
> fix, but it is documented that we must do it.
> 
> CC: Jesse Barnes <jbarnes at virtuousgeek.org>
> CC: Matt Turner <mattst88 at gmail.com>
> Signed-off-by: Ben Widawsky <ben at bwidawsk.net>
> ---
>  drivers/gpu/drm/i915/i915_reg.h |  4 ++++
>  drivers/gpu/drm/i915/intel_pm.c | 18 ++++++++++++++++--
>  2 files changed, 20 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
> index a828e90..13aafa5 100644
> --- a/drivers/gpu/drm/i915/i915_reg.h
> +++ b/drivers/gpu/drm/i915/i915_reg.h
> @@ -4213,6 +4213,10 @@
>  #define   GEN6_READ_OC_PARAMS			0xc
>  #define   GEN6_PCODE_WRITE_MIN_FREQ_TABLE	0x8
>  #define   GEN6_PCODE_READ_MIN_FREQ_TABLE	0x9
> +#define	  GEN6_PCODE_WRITE_RC6VIDS		0x4
> +#define	  GEN6_PCODE_READ_RC6VIDS		0x5
> +#define   GEN6_ENCODE_RC6_VID(mv)		(((mv) / 5) - 245) < 0 ?: 0
> +#define   GEN6_DECODE_RC6_VID(vids)		(((vids) * 5) > 0 ? ((vids) * 5) + 245 : 0)
>  #define GEN6_PCODE_DATA				0x138128
>  #define   GEN6_PCODE_FREQ_IA_RATIO_SHIFT	8
>  
> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> index 6488cd0..9a6edf0 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -2404,10 +2404,10 @@ static void gen6_enable_rps(struct drm_device *dev)
>  	struct intel_ring_buffer *ring;
>  	u32 rp_state_cap;
>  	u32 gt_perf_status;
> -	u32 pcu_mbox, rc6_mask = 0;
> +	u32 rc6vids, pcu_mbox, rc6_mask = 0;
>  	u32 gtfifodbg;
>  	int rc6_mode;
> -	int i;
> +	int i, ret;
>  
>  	WARN_ON(!mutex_is_locked(&dev->struct_mutex));
>  
> @@ -2526,6 +2526,20 @@ static void gen6_enable_rps(struct drm_device *dev)
>  	/* enable all PM interrupts */
>  	I915_WRITE(GEN6_PMINTRMSK, 0);
>  
> +	rc6vids = 0;
> +	ret = sandybridge_pcode_read(dev_priv, GEN6_PCODE_READ_RC6VIDS, &rc6vids);
> +	if (IS_GEN6(dev) && ret) {
> +		DRM_DEBUG_DRIVER("Couldn't check for BIOS workaround\n");
> +	} else if (IS_GEN6(dev) && (GEN6_DECODE_RC6_VID(rc6vids & 0xff) < 450)) {
> +		DRM_ERROR("You should update your BIOS. Correcting minimum rc6 voltage (%dmV->%dmV)\n",
> +			  GEN6_DECODE_RC6_VID(rc6vids & 0xff), 450);
> +		rc6vids &= 0xffff00;
> +		rc6vids |= GEN6_ENCODE_RC6_VID(450);
> +		ret = sandybridge_pcode_write(dev_priv, GEN6_PCODE_WRITE_RC6VIDS, rc6vids);
> +		if (ret)
> +			DRM_ERROR("Couldn't fix incorrect rc6 voltage\n");
> +	}
> +
>  	gen6_gt_force_wake_put(dev_priv);
>  }
>  

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

-- 
Jesse Barnes, Intel Open Source Technology Center