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media: ccs-pll: Avoid overflow in pre-PLL divisor lower bound search 

The external clock frequency times the PLL multiplier may exceed the value
range of 32-bit unsigned integers. Instead perform the same calculation y
using two divisions.

The result has some potential to be different, but that's ok: this number
is used to limit the range of pre-PLL divisors to find optimal values. So
the effect of the rare case of a different result here would mean an
invalid pre-PLL divisor is tried. That will be found out a little later in
any case.

Also guard against dividing by zero if the external clock frequency is
higher than the maximum OP PLL output clock --- a rather improbable case.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
This commit is contained in:
Sakari Ailus 2020-07-07 10:31:56 +02:00 committed by Mauro Carvalho Chehab
parent fe52ece8d2
commit 482e75e7b3
1 changed files with 9 additions and 2 deletions
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11
drivers/media/i2c/ccs-pll.c
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@ -40,6 +40,11 @@ static inline uint32_t is_one_or_even(uint32_t a)
return 1;
}
static inline uint32_t one_or_more(uint32_t a)
{
return a ?: 1;
}
static int bounds_check(struct device *dev, uint32_t val,
uint32_t min, uint32_t max, char *str)
{
@ -458,8 +463,10 @@ int ccs_pll_calculate(struct device *dev, const struct ccs_pll_limits *lim,
min_op_pre_pll_clk_div =
max_t(uint16_t, min_op_pre_pll_clk_div,
clk_div_even_up(
DIV_ROUND_UP(mul * pll->ext_clk_freq_hz,
op_lim_fr->max_pll_op_clk_freq_hz)));
mul /
one_or_more(
DIV_ROUND_UP(op_lim_fr->max_pll_op_clk_freq_hz,
pll->ext_clk_freq_hz))));
dev_dbg(dev, "pll_op check: min / max op_pre_pll_clk_div: %u / %u\n",
min_op_pre_pll_clk_div, max_op_pre_pll_clk_div);