[PATCH v3 4/7] drm/i915: Try harder to get best m, n, p values with minimal error

Shobhit Kumar
2013-12-10T06:45:14Z

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>
---
drivers/gpu/drm/i915/intel_dsi_pll.c | 30 ++++++++++++++++++++----------
1 file changed, 20 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_dsi_pll.c b/drivers/gpu/drm/i915/intel_dsi_pll.c
index 0d1b17f..ba79ec1 100644
--- 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];
--
1.8.3.2