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author | Quanyang Wang <quanyang.wang@windriver.com> | 2022-08-26 17:20:30 +0300 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2022-10-26 14:25:52 +0300 |
commit | 12d31182de8deb7a8e0be6246d661291773427c8 (patch) | |
tree | da5f039340f04e6f2a22f836b0e11195d33be661 /drivers/clk | |
parent | c2257c8a501537afab276c306cb717b7260276e1 (diff) | |
download | linux-12d31182de8deb7a8e0be6246d661291773427c8.tar.xz |
clk: zynqmp: pll: rectify rate rounding in zynqmp_pll_round_rate
[ Upstream commit 30eaf02149ecc3c5815e45d27187bf09e925071d ]
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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Diffstat (limited to 'drivers/clk')
-rw-r--r-- | drivers/clk/zynqmp/pll.c | 31 |
1 files changed, 15 insertions, 16 deletions
diff --git a/drivers/clk/zynqmp/pll.c b/drivers/clk/zynqmp/pll.c index abe6afbf3407..2ae7f9129b07 100644 --- a/drivers/clk/zynqmp/pll.c +++ b/drivers/clk/zynqmp/pll.c @@ -99,26 +99,25 @@ static long zynqmp_pll_round_rate(struct clk_hw *hw, unsigned long rate, unsigned long *prate) { u32 fbdiv; - long rate_div, f; + u32 mult, div; - /* Enable the fractional mode if needed */ - rate_div = (rate * FRAC_DIV) / *prate; - f = rate_div % FRAC_DIV; - if (f) { - if (rate > PS_PLL_VCO_MAX) { - fbdiv = rate / PS_PLL_VCO_MAX; - rate = rate / (fbdiv + 1); - } - if (rate < PS_PLL_VCO_MIN) { - fbdiv = DIV_ROUND_UP(PS_PLL_VCO_MIN, rate); - rate = rate * fbdiv; - } - return rate; + /* Let rate fall inside the range PS_PLL_VCO_MIN ~ PS_PLL_VCO_MAX */ + if (rate > PS_PLL_VCO_MAX) { + div = DIV_ROUND_UP(rate, PS_PLL_VCO_MAX); + rate = rate / div; + } + if (rate < PS_PLL_VCO_MIN) { + mult = DIV_ROUND_UP(PS_PLL_VCO_MIN, rate); + rate = rate * mult; } fbdiv = DIV_ROUND_CLOSEST(rate, *prate); - fbdiv = clamp_t(u32, fbdiv, PLL_FBDIV_MIN, PLL_FBDIV_MAX); - return *prate * fbdiv; + if (fbdiv < PLL_FBDIV_MIN || fbdiv > PLL_FBDIV_MAX) { + fbdiv = clamp_t(u32, fbdiv, PLL_FBDIV_MIN, PLL_FBDIV_MAX); + rate = *prate * fbdiv; + } + + return rate; } /** |