Re: [PATCH] drm/i915: Use SWF06 to figure out max cdclk for BDW

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Fri, Feb 12, 2016 at 05:06:07PM +0200, ville.syrjala@linux.intel.com wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> 
> Bspec tells us that we can allow cdclk up to 540Mhz on BDW ULX, or
> up to 675 MHz on ULT, bu only if extra cooling is provided. There
> don't seem to be any strap or VBT bits to tells us this however.
> 
> But I did spot something potentially relevant in
> VBIOS_GOP_Driver_SWF_Registers.pdf. Apparently VBIOS/GOP can pass
> the max cdclk frequeny in SWF06 to the driver. Let's assume the firmware
> knows what its doing and trust the max cdclk in SWF06 if it's higher
> than the basic limit specified in Bspec. To avoid regressing anything
> let's ignore SWF06 if it indicates a lower limit than Bspec.
> 
> Cc: Clint Taylor <clinton.a.taylor@intel.com>
> Cc: "Thulasimani, Sivakumar" <sivakumar.thulasimani@intel.com>
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> ---
> 
> I'm not at all sure if this is the right way to go about it. Sivakumar,
> since you seem to have some ideas on this maybe you can have a look.
> I'm not aware of any complaints so far that people can't get the cdclk
> as high is they should on specific machines, so not sure if this is really
> even needed.
> 
> The other open question is what we should do if the VBIOS limit is
> lower than what we'd expect based on BSpec. Should we still trust it?
> Sadly we can't verify the SWF06 cdclk value in any way since it
> only has two bits and we have four possible cdclk values.

Oh, and I forgot to mention that this is totally untested.

> 
>  drivers/gpu/drm/i915/intel_display.c | 60 ++++++++++++++++++++++++++++--------
>  1 file changed, 47 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 836bbdc239b6..1d70f6bf2934 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -5407,21 +5407,55 @@ static void intel_update_max_cdclk(struct drm_device *dev)
>  			dev_priv->max_cdclk_freq = 450000;
>  		else
>  			dev_priv->max_cdclk_freq = 337500;
> -	} else if (IS_BROADWELL(dev))  {
> +	} else if (IS_BROADWELL(dev)) {
> +		int bios_max_cdclk_freq, max_cdclk_freq;
> +
>  		/*
> -		 * FIXME with extra cooling we can allow
> -		 * 540 MHz for ULX and 675 Mhz for ULT.
> -		 * How can we know if extra cooling is
> -		 * available? PCI ID, VTB, something else?
> +		 * With extra cooling we can allow 540 MHz for
> +		 * ULX and 675 Mhz for ULT. Assume VBIOS/GOP
> +		 * passes that information in SWF06.
>  		 */
> -		if (I915_READ(FUSE_STRAP) & HSW_CDCLK_LIMIT)
> -			dev_priv->max_cdclk_freq = 450000;
> -		else if (IS_BDW_ULX(dev))
> -			dev_priv->max_cdclk_freq = 450000;
> -		else if (IS_BDW_ULT(dev))
> -			dev_priv->max_cdclk_freq = 540000;
> -		else
> -			dev_priv->max_cdclk_freq = 675000;
> +		switch (I915_READ(SWF_ILK(0x06)) & 0x3) {
> +		case 0:
> +			bios_max_cdclk_freq = 450000;
> +			break;
> +		case 1:
> +			bios_max_cdclk_freq = 540000;
> +			break;
> +		case 2:
> +			bios_max_cdclk_freq = 337500;
> +			break;
> +		case 3:
> +			bios_max_cdclk_freq = 675000;
> +			break;
> +		}
> +
> +		if (I915_READ(FUSE_STRAP) & HSW_CDCLK_LIMIT) {
> +			if (WARN_ON(bios_max_cdclk_freq != 450000))
> +				bios_max_cdclk_freq = 450000;
> +			max_cdclk_freq = 450000;
> +		} else if (IS_BDW_ULX(dev_priv)) {
> +			if (WARN_ON(bios_max_cdclk_freq > 540000))
> +				bios_max_cdclk_freq = 540000;
> +			max_cdclk_freq = 450000;
> +		} else if (IS_BDW_ULT(dev_priv)) {
> +			max_cdclk_freq = 540000;
> +		} else {
> +			max_cdclk_freq = 675000;
> +		}
> +
> +		if (bios_max_cdclk_freq > max_cdclk_freq) {
> +			DRM_DEBUG_KMS("VBIOS/GOP max cdclk (%d kHz) higher than basic limit (%d kHz), "
> +				      "assuming extra cooling is present\n",
> +				      bios_max_cdclk_freq, max_cdclk_freq);
> +			max_cdclk_freq = bios_max_cdclk_freq;
> +		} else if (bios_max_cdclk_freq < max_cdclk_freq) {
> +			DRM_DEBUG_KMS("VBIOS/GOP max cdclk (%d kHz) lower than basic limit (%d kHz), "
> +				      "ignoring it\n",
> +				      bios_max_cdclk_freq, max_cdclk_freq);
> +		}
> +
> +		dev_priv->max_cdclk_freq = max_cdclk_freq;
>  	} else if (IS_CHERRYVIEW(dev)) {
>  		dev_priv->max_cdclk_freq = 320000;
>  	} else if (IS_VALLEYVIEW(dev)) {
> -- 
> 2.4.10

-- 
Ville Syrjälä
Intel OTC
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