Re: [PATCH 3/3] drm/i915: Use the ceil value for the additional clk divider

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

On Fri, Dec 04, 2015 at 07:47:39PM +0530, Deepak M wrote:
> Additional clock value divider should use the ceil
> value of the calulation to get the correct divider value.
> 
> Signed-off-by: Deepak M <m.deepak@intel.com>
> ---
>  drivers/gpu/drm/i915/intel_dsi_pll.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_dsi_pll.c b/drivers/gpu/drm/i915/intel_dsi_pll.c
> index cb3cf39..1322a71 100644
> --- a/drivers/gpu/drm/i915/intel_dsi_pll.c
> +++ b/drivers/gpu/drm/i915/intel_dsi_pll.c
> @@ -454,7 +454,7 @@ static void bxt_dsi_program_clocks(struct drm_device *dev, enum port port)
>  	dsi_rate = (BXT_REF_CLOCK_KHZ * pll_ratio) / 2;
>  
>  	/* Max possible output of clock is 39.5 MHz, program value -1 */
> -	divider = (dsi_rate / BXT_MAX_VAR_OUTPUT_KHZ) - 1;
> +	divider = DIV_ROUND_UP(dsi_rate, BXT_MAX_VAR_OUTPUT_KHZ) - 1;

I can't find anything to support the 39.5 MHz claim above. I do know the
tx escape clock should be <=20Mhz, so with the /2 extra divider it
seems we should aim for <=40Mhz here. So yes, round up does make sense,
but it seems to me that BXT_MAX_VAR_OUTPUT_KHZ should be 40 MHz.

>  	tmp |= BXT_MIPI_ESCLK_VAR_DIV(port, divider);
>  
>  	/*
> -- 
> 1.9.1
> 
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-- 
Ville Syrjälä
Intel OTC
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