Re: [PATCH 1/8] drm/i915: Don't factor in pixel multplier when deriving dotclock from link clock and M/N values

[Jani Nikula <jani.nikula@linux.intel.com>]

On Wed, 04 Sep 2013, ville.syrjala@linux.intel.com wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
>
> We feed the non-multiplied clock to intel_link_compute_m_n(), so the
> opposite operation should use the same order of operations. So we just
> multiply by pixel_multiplier in the end now.

Reviewed-by: Jani Nikula <jani.nikula@intel.com>


>
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/intel_display.c | 15 +++++++--------
>  1 file changed, 7 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index d88057e..b45c6e6 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -7340,20 +7340,18 @@ static void ironlake_crtc_clock_get(struct intel_crtc *crtc,
>  	struct drm_device *dev = crtc->base.dev;
>  	struct drm_i915_private *dev_priv = dev->dev_private;
>  	enum transcoder cpu_transcoder = pipe_config->cpu_transcoder;
> -	int link_freq, repeat;
> +	int link_freq;
>  	u64 clock;
>  	u32 link_m, link_n;
>  
> -	repeat = pipe_config->pixel_multiplier;
> -
>  	/*
>  	 * The calculation for the data clock is:
> -	 * pixel_clock = ((m/n)*(link_clock * nr_lanes * repeat))/bpp
> +	 * pixel_clock = ((m/n)*(link_clock * nr_lanes))/bpp
>  	 * But we want to avoid losing precison if possible, so:
> -	 * pixel_clock = ((m * link_clock * nr_lanes * repeat)/(n*bpp))
> +	 * pixel_clock = ((m * link_clock * nr_lanes)/(n*bpp))
>  	 *
>  	 * and the link clock is simpler:
> -	 * link_clock = (m * link_clock * repeat) / n
> +	 * link_clock = (m * link_clock) / n
>  	 */
>  
>  	/*
> @@ -7375,10 +7373,11 @@ static void ironlake_crtc_clock_get(struct intel_crtc *crtc,
>  	if (!link_m || !link_n)
>  		return;
>  
> -	clock = ((u64)link_m * (u64)link_freq * (u64)repeat);
> +	clock = ((u64)link_m * (u64)link_freq);
>  	do_div(clock, link_n);
>  
> -	pipe_config->adjusted_mode.clock = clock;
> +	pipe_config->adjusted_mode.clock = clock *
> +		pipe_config->pixel_multiplier;
>  }
>  
>  /** Returns the currently programmed mode of the given pipe. */
> -- 
> 1.8.1.5
>
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-- 
Jani Nikula, Intel Open Source Technology Center
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