Re: [PATCH] drm/i915/glk: CDCLK calculation changes for glk

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

On Tue, Feb 07, 2017 at 05:48:46AM -0500, Madhav Chauhan wrote:
> As per BSPEC, valid cdclk values for glk are 79.2, 158.4, 316.8 Mhz.
> Practically we can achive only 99% of these cdclk values. So cdclk
> should be calculated for the given pixclk as per that otherwise it may
> lead to screen corruption for some scenarios.

I this caused by the hw actually requiring some guardband or simply
because of our sucky DPLL code not updating the dotclock with the actual
value the hw is going to produce?

If it's a genuine hw limitation is it documented? And if not has
someone filed a spec issue for it? And what about other platforms
(GLK isn't the only one without a guardband in our code after all)?

> 
> Signed-off-by: Madhav Chauhan <madhav.chauhan@intel.com>
> ---
>  drivers/gpu/drm/i915/intel_display.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 45e5874..2e1bfe9 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -6544,9 +6544,9 @@ static int valleyview_calc_cdclk(struct drm_i915_private *dev_priv,
>  
>  static int glk_calc_cdclk(int max_pixclk)
>  {
> -	if (max_pixclk > 2 * 158400)
> +	if (max_pixclk > DIV_ROUND_UP(2 * 158400 * 99, 100))
>  		return 316800;
> -	else if (max_pixclk > 2 * 79200)
> +	else if (max_pixclk > DIV_ROUND_UP(2 * 79200 * 99, 100))
>  		return 158400;
>  	else
>  		return 79200;
> -- 
> 1.9.1
> 
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-- 
Ville Syrjälä
Intel OTC
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