Re: [PATCH 1/3] drm/i915: Update CDCLK_FREQ register on BDW after changing cdclk frequency

[Mika Kahola <mika.kahola@intel.com>]

Indeed, BSpec says that this register should be programmed by CD clock
minus one.

Reviewed-by: Mika Kahola <mika.kahola@intel.com>

On Tue, 2016-04-26 at 19:46 +0300, ville.syrjala@linux.intel.com wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> 
> Update CDCLK_FREQ on BDW after changing the cdclk frequency. Not sure
> if this is a late addition to the spec, or if I simply overlooked this
> step when writing the original code.
> 
> This is what Bspec has to say about CDCLK_FREQ:
> "Program this field to the CD clock frequency minus one. This is used to
>  generate a divided down clock for miscellaneous timers in display."
> 
> And the "Broadwell Sequences for Changing CD Clock Frequency" section
> clarifies this further:
> "For CD clock 337.5 MHz, program 337 decimal.
>  For CD clock 450 MHz, program 449 decimal.
>  For CD clock 540 MHz, program 539 decimal.
>  For CD clock 675 MHz, program 674 decimal."
> 
> Cc: stable@vger.kernel.org
> Cc: Mika Kahola <mika.kahola@intel.com>
> Fixes: b432e5cfd5e9 ("drm/i915: BDW clock change support")
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/i915_reg.h      | 2 ++
>  drivers/gpu/drm/i915/intel_display.c | 2 ++
>  2 files changed, 4 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
> index 03264fd30fdd..41c9ae03652b 100644
> --- a/drivers/gpu/drm/i915/i915_reg.h
> +++ b/drivers/gpu/drm/i915/i915_reg.h
> @@ -7484,6 +7484,8 @@ enum skl_disp_power_wells {
>  #define  TRANS_CLK_SEL_DISABLED		(0x0<<29)
>  #define  TRANS_CLK_SEL_PORT(x)		(((x)+1)<<29)
>  
> +#define CDCLK_FREQ			_MMIO(0x46200)
> +
>  #define _TRANSA_MSA_MISC		0x60410
>  #define _TRANSB_MSA_MISC		0x61410
>  #define _TRANSC_MSA_MISC		0x62410
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 929fd93b3e5d..ea55dd331fac 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -9647,6 +9647,8 @@ static void broadwell_set_cdclk(struct drm_device *dev, int cdclk)
>  	sandybridge_pcode_write(dev_priv, HSW_PCODE_DE_WRITE_FREQ_REQ, data);
>  	mutex_unlock(&dev_priv->rps.hw_lock);
>  
> +	I915_WRITE(CDCLK_FREQ, DIV_ROUND_CLOSEST(cdclk, 1000) - 1);
> +
>  	intel_update_cdclk(dev);
>  
>  	WARN(cdclk != dev_priv->cdclk_freq,

-- 
Mika Kahola - Intel OTC