On Tue, Jul 04, 2017 at 11:04:56PM +0300, Priit Laes wrote:
> SATA clock on sun4i/sun7i is of type (parent) / M / 6 where
> 6 is fixed post-divider.
>
> Signed-off-by: Priit Laes <pl...@plaes.org>
> ---
> drivers/clk/sunxi-ng/ccu_div.c | 18 ++++++++++++++++--
> drivers/clk/sunxi-ng/ccu_div.h | 3 ++-
> 2 files changed, 18 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/clk/sunxi-ng/ccu_div.c b/drivers/clk/sunxi-ng/ccu_div.c
> index c0e5c10..054b12a 100644
> --- a/drivers/clk/sunxi-ng/ccu_div.c
> +++ b/drivers/clk/sunxi-ng/ccu_div.c
> @@ -21,6 +21,9 @@ static unsigned long ccu_div_round_rate(struct
> ccu_mux_internal *mux,
> {
> struct ccu_div *cd = data;
>
> + if (cd->common.features & CCU_FEATURE_FIXED_POSTDIV)
> + rate /= cd->fixed_post_div;
> +
> return divider_round_rate_parent(&cd->common.hw, parent,
> rate, parent_rate,
> cd->div.table, cd->div.width,
This doesn't work.
The rate formula is
rate = parent / div / 6
Which is equivalent to
div = rate * 6 / parent
You should be multiplying the rate, not dividing it (or dividing the
parent, but then you'll also need to multiply it back after the call
to divider_round_rate_parent).
Consider this, some driver wants to set a rate of 100MHz on this
clock. The parent is 1.2GHz, and you have your postdiv of 6.
The divider we want to compute is 2, obviously.
You're doing here:
rate / 6 = parent / div
Which means that you'll end up trying to find the divider between
1.2GHz and 16.6666MHz, which is going to be 72.
> @@ -62,8 +65,13 @@ static unsigned long ccu_div_recalc_rate(struct clk_hw *hw,
> parent_rate = ccu_mux_helper_apply_prediv(&cd->common, &cd->mux, -1,
> parent_rate);
>
> - return divider_recalc_rate(hw, parent_rate, val, cd->div.table,
> - cd->div.flags);
> + val = divider_recalc_rate(hw, parent_rate, val, cd->div.table,
> + cd->div.flags);
> +
> + if (cd->common.features & CCU_FEATURE_FIXED_POSTDIV)
> + val /= cd->fixed_post_div;
> +
> + return val;
> }
>
> static int ccu_div_determine_rate(struct clk_hw *hw,
> @@ -71,6 +79,9 @@ static int ccu_div_determine_rate(struct clk_hw *hw,
> {
> struct ccu_div *cd = hw_to_ccu_div(hw);
>
> + if (cd->common.features & CCU_FEATURE_FIXED_POSTDIV)
> + req->rate *= cd->fixed_post_div;
> +
I guess this is why you never really saw the issue. Combined with your
division in ccu_div_round_rate, it produces the exact rate you were
given as an argument.
> return ccu_mux_helper_determine_rate(&cd->common, &cd->mux,
> req, ccu_div_round_rate, cd);
> }
> @@ -89,6 +100,9 @@ static int ccu_div_set_rate(struct clk_hw *hw, unsigned
> long rate,
> val = divider_get_val(rate, parent_rate, cd->div.table, cd->div.width,
> cd->div.flags);
>
> + if (cd->common.features & CCU_FEATURE_FIXED_POSTDIV)
> + val /= cd->fixed_post_div;
> +
If you multiply the rate before calling divider_get_val, you won't
have to do the division of the divider, with all the rounding
weirdness it might create.
Maxime
--
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com
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