drm/i915: Try harder to get best m, n, p values with minimal error

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.

v2: Use signed variable for target and calculated dsi clock values

Signed-off-by: Vijayakumar Balakrishnan <vijayakumar.balakrishnan@intel.com>
Signed-off-by: Shobhit Kumar <shobhit.kumar@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

diff --git a/drivers/gpu/drm/i915/intel_dsi_pll.c b/drivers/gpu/drm/i915/intel_dsi_pll.c
index 0d1b17f..ba79ec1 100644 (file)
--- a/drivers/gpu/drm/i915/intel_dsi_pll.c
+++ b/drivers/gpu/drm/i915/intel_dsi_pll.c
@@ -169,8 +169,8 @@ static int dsi_calc_mnp(u32 dsi_clk, struct dsi_mnp *dsi_mnp)
        u32 ref_clk;
        u32 error;
        u32 tmp_error;
-       u32 target_dsi_clk;
-       u32 calc_dsi_clk;
+       int target_dsi_clk;
+       int calc_dsi_clk;
        u32 calc_m;
        u32 calc_p;
        u32 m_seed;
@@ -184,22 +184,32 @@ 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);
+
+                       if (tmp_error < error) {
+                               error = tmp_error;
+                               calc_m = m;
+                               calc_p = p;
                        }
                }
+
+               if (error == 0)
+                       break;
        }
 
        m_seed = lfsr_converts[calc_m - 62];