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![]() The function zynqmp_pll_round_rate is used to find a most appropriate PLL frequency which the hardware can generate according to the desired frequency. For example, if the desired frequency is 297MHz, considering the limited range from PS_PLL_VCO_MIN (1.5GHz) to PS_PLL_VCO_MAX (3.0GHz) of PLL, zynqmp_pll_round_rate should return 1.872GHz (297MHz * 5). There are two problems with the current code of zynqmp_pll_round_rate: 1) When the rate is below PS_PLL_VCO_MIN, it can't find a correct rate when the parameter "rate" is an integer multiple of *prate, in other words, if "f" is zero, zynqmp_pll_round_rate won't return a valid frequency which is from PS_PLL_VCO_MIN to PS_PLL_VCO_MAX. For example, *prate is 33MHz and the rate is 660MHz, zynqmp_pll_round_rate will not boost up rate and just return 660MHz, and this will cause clk_calc_new_rates failure since zynqmp_pll_round_rate returns an invalid rate out of its boundaries. 2) Even if the rate is higher than PS_PLL_VCO_MIN, there is still a risk that zynqmp_pll_round_rate returns an invalid rate because the function DIV_ROUND_CLOSEST makes some loss in the fractional part. If the parent clock *prate is 33333333Hz and we want to set the PLL rate to 1.5GHz, this function will return 1499999985Hz by using the formula below: value = *prate * DIV_ROUND_CLOSEST(rate, *prate)). This value is also invalid since it's slightly smaller than PS_PLL_VCO_MIN. because DIV_ROUND_CLOSEST makes some loss in the fractional part. Signed-off-by: Quanyang Wang <quanyang.wang@windriver.com> Link: https://lore.kernel.org/r/20220826142030.213805-1-quanyang.wang@windriver.com Reviewed-by: Shubhrajyoti Datta <shubhrajyoti.datta@amd.com> Signed-off-by: Stephen Boyd <sboyd@kernel.org> |
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.. | ||
clk-gate-zynqmp.c | ||
clk-mux-zynqmp.c | ||
clk-zynqmp.h | ||
clkc.c | ||
divider.c | ||
Kconfig | ||
Makefile | ||
pll.c |