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SubjectRe: [PATCH 5/6] clk: at91: clk-generated: make gclk determine audio_pll rate
On Fri, 23 Jun 2017 11:00:58 +0200
Quentin Schulz <quentin.schulz@free-electrons.com> wrote:

> This allows gclk to determine audio_pll rate and set the parent rate
> accordingly.
>
> However, there are multiple children clocks that could technically
> change the rate of audio_pll. Since the clock rate is usually critical
> for IPs, it isn't a good idea to have multiple clocks changing audio_pll
> clock rate. There isn't any rate locking system for the moment, thus
> we enforce that classd_gclk be the only one allowed to change audio_pll
> rate. To remain consistent, we deny other clocks to be children of
> audio_pll so classd_gclk altering audio_pll rate does not impact any
> other device.
>
> This needs to be re-worked once we have a rate locking system so two
> clocks could be children of the same clock and be sure the clock rate
> isn't changed by one or the other.
>
> Signed-off-by: Quentin Schulz <quentin.schulz@free-electrons.com>
> ---
> drivers/clk/at91/clk-generated.c | 41 ++++++++++++++++++++++++++++++++++------
> 1 file changed, 35 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/clk/at91/clk-generated.c b/drivers/clk/at91/clk-generated.c
> index 6530a2e7e84d..e66ee735a569 100644
> --- a/drivers/clk/at91/clk-generated.c
> +++ b/drivers/clk/at91/clk-generated.c
> @@ -26,6 +26,9 @@
> #define GENERATED_SOURCE_MAX 6
> #define GENERATED_MAX_DIV 255
>
> +#define GCK_ID_CLASSD 59
> +#define GCK_INDEX_DT_AUDIO_PLL 5
> +
> struct clk_generated {
> struct clk_hw hw;
> struct regmap *regmap;
> @@ -126,15 +129,14 @@ static int clk_generated_determine_rate(struct clk_hw *hw,
> {
> struct clk_generated *gck = to_clk_generated(hw);
> struct clk_hw *parent = NULL;
> + struct clk_rate_request req_parent = *req;
> long best_rate = -EINVAL;
> - unsigned long min_rate;
> + unsigned long min_rate, parent_rate;
> int best_diff = -1;
> int i;
> + u32 div;
>
> - for (i = 0; i < clk_hw_get_num_parents(hw); i++) {
> - u32 div;
> - unsigned long parent_rate;
> -
> + for (i = 0; i < clk_hw_get_num_parents(hw) - 1; i++) {
> parent = clk_hw_get_parent_by_index(hw, i);
> if (!parent)
> continue;
> @@ -150,11 +152,37 @@ static int clk_generated_determine_rate(struct clk_hw *hw,
> clk_generated_best_diff(req, parent, parent_rate, div,
> &best_diff, &best_rate);
>
> + if (!best_diff)
> + break;
> + }
> +
> + /*
> + * The audio_pll rate can be modified unlike the five others clocks that
> + * should never be altered.
> + * The audio_pll can technically be used by multiple consumers. However,
> + * they all are likely to want to modify its rate while the rate is
> + * critical for each one. Since we do not have a rate locking for the
> + * moment, let classd_gclk be the only consumer of the audio_pll clock.
> + */
> +
> + if (gck->id != GCK_ID_CLASSD)
> + goto end;

As discussed on IRC with Nicolas and Cyrille, it seems we have other
potential users of the audio-pll: SSC and I2S. Can you extend the test
to let these GCK clks take the audio-pll?

> +
> + parent = clk_hw_get_parent_by_index(hw, GCK_INDEX_DT_AUDIO_PLL);
> + if (!parent)
> + goto end;
> +
> + for (div = 1; div < GENERATED_MAX_DIV + 2; div++) {
> + req_parent.rate = req->rate * div;
> + __clk_determine_rate(parent, &req_parent);
> + clk_generated_best_diff(req, parent, req_parent.rate, div,
> + &best_diff, &best_rate);
>
> if (!best_diff)
> break;
> }
>
> +end:
> pr_debug("GCLK: %s, best_rate = %ld, parent clk: %s @ %ld\n",
> __func__, best_rate,
> __clk_get_name((req->best_parent_hw)->clk),
> @@ -264,7 +292,8 @@ at91_clk_register_generated(struct regmap *regmap, spinlock_t *lock,
> init.ops = &generated_ops;
> init.parent_names = parent_names;
> init.num_parents = num_parents;
> - init.flags = CLK_SET_RATE_GATE | CLK_SET_PARENT_GATE;
> + init.flags = CLK_SET_RATE_GATE | CLK_SET_PARENT_GATE |
> + CLK_SET_RATE_PARENT;
>
> gck->id = id;
> gck->hw.init = &init;

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