From: Ahmad Fatoum <[email protected]> This is an adoption of the corresponding Linux commit:
| commit da321133b53caf7889ed3ca1dabe4cc368db2604 | Author: Uwe Kleine-König <[email protected]> | Date: Sat Feb 21 11:40:23 2015 +0100 | | clk: divider: fix calculation of maximal parent rate for a given divider | | The rate provided at the output of a clk-divider is calculated as: | | DIV_ROUND_UP(parent_rate, div) | | since commit b11d282dbea2 (clk: divider: fix rate calculation for | fractional rates). So to yield a rate not bigger than r parent_rate | must be <= r * div. | | The effect of choosing a parent rate that is too big as was done before | this patch results in wrongly ruling out good dividers. | | Note that this is not a complete fix as __clk_round_rate might return a | value >= its 2nd parameter. Also for dividers with | CLK_DIVIDER_ROUND_CLOSEST set the calculation is not accurate. But this | fixes the test case by Sascha Hauer that uses a chain of three dividers | under a fixed clock. | | Fixes: b11d282dbea2 (clk: divider: fix rate calculation for fractional rates) | Suggested-by: Sascha Hauer <[email protected]> | Signed-off-by: Uwe Kleine-König <[email protected]> | Acked-by: Sascha Hauer <[email protected]> | Signed-off-by: Michael Turquette <[email protected]> The "not a complete fix" caveat applies here as well: barebox' clk_round_rate() falls back to clk_get_rate() for a clock without a round_rate op, and clk_mux_round_rate() returns the closest parent rate, so both can return more than they were asked for and clk_divider_bestdiv() can still end up without a candidate. CLK_DIVIDER_ROUND_CLOSEST doesn't exist in barebox, so that half of the caveat doesn't apply. With the previous commit, the i.MX6 IPU pixel clocks now hit their requested rates exactly, e.g. on a SABRE Lite: clk_round_rate ipu1_di0 65000000 -> 65000000 (was 40500000) clk_round_rate ipu1_di0 148500000 -> 148500000 (was 148500001) Fixes: d4aaca3647fe ("clk: clk-divider: sync with kernel code") Reported-by: Claude:opus-5 Signed-off-by: Ahmad Fatoum <[email protected]> --- drivers/clk/clk-divider.c | 9 +-------- 1 file changed, 1 insertion(+), 8 deletions(-) diff --git a/drivers/clk/clk-divider.c b/drivers/clk/clk-divider.c index 8e630ccde4e6..2c97742cec0e 100644 --- a/drivers/clk/clk-divider.c +++ b/drivers/clk/clk-divider.c @@ -112,12 +112,6 @@ static unsigned long clk_divider_recalc_rate(struct clk_hw *hw, divider->flags, divider->width); } -/* - * The reverse of DIV_ROUND_UP: The maximum number which - * divided by m is r - */ -#define MULT_ROUND_UP(r, m) ((r) * (m) + (m) - 1) - static bool _is_valid_table_div(const struct clk_div_table *table, unsigned int div) { @@ -211,8 +205,7 @@ static int clk_divider_bestdiv(struct clk *clk, unsigned long rate, *best_parent_rate = parent_rate_saved; return i; } - parent_rate = clk_round_rate(clk_get_parent(clk), - MULT_ROUND_UP(rate, i)); + parent_rate = clk_round_rate(clk_get_parent(clk), rate * i); now = DIV_ROUND_UP_ULL((u64)parent_rate, i); if (now <= rate && now > best) { bestdiv = i; -- 2.47.3
