Re: [PATCH v2] drm/i915/dsi: add support for DSI PLL N1 divisor values

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

On Wed, May 13, 2015 at 10:35:25AM +0300, Jani Nikula wrote:
> Currently DSI PLL N1 is hardcoded off. Make it possible to use it
> later. This should have no functional changes for now.
> 
> v2: s/ffz(~(n))/ffs(n) - 1/ (Ville)
> 
> Signed-off-by: Jani Nikula <jani.nikula@intel.com>

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

> ---
>  drivers/gpu/drm/i915/intel_dsi_pll.c | 17 +++++++++++------
>  1 file changed, 11 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_dsi_pll.c b/drivers/gpu/drm/i915/intel_dsi_pll.c
> index 9ada06ec88e5..3a6c2335991c 100644
> --- a/drivers/gpu/drm/i915/intel_dsi_pll.c
> +++ b/drivers/gpu/drm/i915/intel_dsi_pll.c
> @@ -160,7 +160,7 @@ static u32 dsi_clk_from_pclk(u32 pclk, int pixel_format, int lane_count)
>  static int dsi_calc_mnp(int target_dsi_clk, struct dsi_mnp *dsi_mnp)
>  {
>  	unsigned int calc_m = 0, calc_p = 0;
> -	unsigned int m, n, p;
> +	unsigned int m, n = 1, p;
>  	int ref_clk = 25000;
>  	int delta = target_dsi_clk;
>  	u32 m_seed;
> @@ -177,7 +177,7 @@ static int dsi_calc_mnp(int target_dsi_clk, struct dsi_mnp *dsi_mnp)
>  			 * Find the optimal m and p divisors with minimal delta
>  			 * +/- the required clock
>  			 */
> -			int calc_dsi_clk = (m * ref_clk) / p;
> +			int calc_dsi_clk = (m * ref_clk) / (p * n);
>  			int d = abs(target_dsi_clk - calc_dsi_clk);
>  			if (d < delta) {
>  				delta = d;
> @@ -187,10 +187,11 @@ static int dsi_calc_mnp(int target_dsi_clk, struct dsi_mnp *dsi_mnp)
>  		}
>  	}
>  
> +	/* register has log2(N1), this works fine for powers of two */
> +	n = ffs(n) - 1;
>  	m_seed = lfsr_converts[calc_m - 62];
> -	n = 1;
>  	dsi_mnp->dsi_pll_ctrl = 1 << (DSI_PLL_P1_POST_DIV_SHIFT + calc_p - 2);
> -	dsi_mnp->dsi_pll_div = (n - 1) << DSI_PLL_N1_DIV_SHIFT |
> +	dsi_mnp->dsi_pll_div = n << DSI_PLL_N1_DIV_SHIFT |
>  		m_seed << DSI_PLL_M1_DIV_SHIFT;
>  
>  	return 0;
> @@ -293,7 +294,7 @@ u32 vlv_get_dsi_pclk(struct intel_encoder *encoder, int pipe_bpp)
>  	struct intel_dsi *intel_dsi = enc_to_intel_dsi(&encoder->base);
>  	u32 dsi_clock, pclk;
>  	u32 pll_ctl, pll_div;
> -	u32 m = 0, p = 0;
> +	u32 m = 0, p = 0, n;
>  	int refclk = 25000;
>  	int i;
>  
> @@ -308,6 +309,10 @@ u32 vlv_get_dsi_pclk(struct intel_encoder *encoder, int pipe_bpp)
>  	pll_ctl &= DSI_PLL_P1_POST_DIV_MASK;
>  	pll_ctl = pll_ctl >> (DSI_PLL_P1_POST_DIV_SHIFT - 2);
>  
> +	/* N1 divisor */
> +	n = (pll_div & DSI_PLL_N1_DIV_MASK) >> DSI_PLL_N1_DIV_SHIFT;
> +	n = 1 << n; /* register has log2(N1) */
> +
>  	/* mask out the other bits and extract the M1 divisor */
>  	pll_div &= DSI_PLL_M1_DIV_MASK;
>  	pll_div = pll_div >> DSI_PLL_M1_DIV_SHIFT;
> @@ -335,7 +340,7 @@ u32 vlv_get_dsi_pclk(struct intel_encoder *encoder, int pipe_bpp)
>  
>  	m = i + 62;
>  
> -	dsi_clock = (m * refclk) / p;
> +	dsi_clock = (m * refclk) / (p * n);
>  
>  	/* pixel_format and pipe_bpp should agree */
>  	assert_bpp_mismatch(intel_dsi->pixel_format, pipe_bpp);
> -- 
> 2.1.4

-- 
Ville Syrjälä
Intel OTC
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