On Sat, 09 Nov 2013, Shobhit Kumar <[email protected]> wrote:
> Basically check for both +ive and -ive deviation from target clock and
> pick the one with minimal error. If we get a direct match, break from
> loop to acheive some optimization.
>
> Signed-off-by: Vijayakumar Balakrishnan <[email protected]>
> Signed-off-by: Shobhit Kumar <[email protected]>
> ---
> drivers/gpu/drm/i915/intel_dsi_pll.c | 26 ++++++++++++++++++--------
> 1 file changed, 18 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_dsi_pll.c
> b/drivers/gpu/drm/i915/intel_dsi_pll.c
> index 9f3e6b0..16bc6b2 100644
> --- a/drivers/gpu/drm/i915/intel_dsi_pll.c
> +++ b/drivers/gpu/drm/i915/intel_dsi_pll.c
> @@ -243,22 +243,32 @@ static int dsi_calc_mnp(u32 dsi_clk, struct dsi_mnp
> *dsi_mnp)
> ref_clk = 25000;
> target_dsi_clk = dsi_clk;
> error = 0xFFFFFFFF;
> + tmp_error = 0xFFFFFFFF;
> calc_m = 0;
> calc_p = 0;
>
> for (m = 62; m <= 92; m++) {
> for (p = 2; p <= 6; p++) {
> -
> + /* Find the optimal m and p divisors
> + with minimal error +/- the required clock */
> calc_dsi_clk = (m * ref_clk) / p;
> - if (calc_dsi_clk >= target_dsi_clk) {
> - tmp_error = calc_dsi_clk - target_dsi_clk;
> - if (tmp_error < error) {
> - error = tmp_error;
> - calc_m = m;
> - calc_p = p;
> - }
> + if (calc_dsi_clk == target_dsi_clk) {
> + calc_m = m;
> + calc_p = p;
> + error = 0;
> + break;
> + } else
> + tmp_error = abs(target_dsi_clk - calc_dsi_clk);
This is fragile, and only works because of the kernel's implementation
of abs(). The substraction should be done with signed values.
BR,
Jani.
> +
> + if (tmp_error < error) {
> + error = tmp_error;
> + calc_m = m;
> + calc_p = p;
> }
> }
> +
> + if (error == 0)
> + break;
> }
>
> m_seed = lfsr_converts[calc_m - 62];
> --
> 1.7.9.5
>
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--
Jani Nikula, Intel Open Source Technology Center
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