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>

diff --git a/drivers/media/i2c/ccs-pll.c b/drivers/media/i2c/ccs-pll.c
index b45e6b30c528c54401a1ce44b9f61d79ef45b004..78897a7c1448d71e988a92804bf9a8d8eb42c9a5 100644 (file)
--- a/drivers/media/i2c/ccs-pll.c
+++ b/drivers/media/i2c/ccs-pll.c
@@ -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);