From 4d3f36c5e9ca0f947eed71660239c529c501141a Mon Sep 17 00:00:00 2001 From: Mike Looijmans Date: Thu, 31 May 2018 16:03:55 +0200 Subject: [PATCH] clk-si544: Properly round requested frequency to nearest match The si544 driver had a rounding problem that using the result of clk_round_rate may set the clock to yet another rate, for example: clk_round_rate(195000000) = 194999999 clk_round_rate(194999999) = 194999998 Clients would expect that after clk_set_rate(clk, freq2=clk_round_rate(clk, freq)) the chip will be running at exactly freq2. The problem was in the calculation of the feedback divider, it was always rounded down instead of to the nearest possible VCO value. After this change, the following holds true for any supported frequency: actual_freq = clk_round_rate(clk, freq); clk_set_rate(clk, actual_freq); clk_round_rate(clk, actual_freq) == actual_freq && clk_get_rate(clk) == actual_freq Signed-off-by: Mike Looijmans Fixes: 953cc3e81170 ("clk: Add driver for the si544 clock generator chip") Signed-off-by: Stephen Boyd --- drivers/clk/clk-si544.c | 1 + 1 file changed, 1 insertion(+) diff --git a/drivers/clk/clk-si544.c b/drivers/clk/clk-si544.c index 1c96a9f6c022..1e2a3b8f9454 100644 --- a/drivers/clk/clk-si544.c +++ b/drivers/clk/clk-si544.c @@ -207,6 +207,7 @@ static int si544_calc_muldiv(struct clk_si544_muldiv *settings, /* And the fractional bits using the remainder */ vco = (u64)tmp << 32; + vco += FXO / 2; /* Round to nearest multiple */ do_div(vco, FXO); settings->fb_div_frac = vco; -- 2.11.0