[PATCH v2 6/9] clk: at91: clk-generated: make gclk determine audio_pll rate

Nicolas Ferre
2017-07-06T15:29:22Z

On 04/07/2017 at 13:59, Quentin Schulz 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 (via gck). With the rate locking, the first
> consumer to enable the clock will be the one definitely setting the rate
> of the clock.
>
> Since audio IPs are most likely to request the same rate, we enforce
> that the only clks able to modify gck rate are those of audio IPs.
>
> To remain consistent, we deny other clocks to be children of audio_pll.
>
> Signed-off-by: Quentin Schulz <quentin.schulz@free-electrons.com>
> ---
>
> v2:
> - added conditions for audio pll rate setting restriction for SSC and
> I2S,
>
> drivers/clk/at91/clk-generated.c | 48 +++++++++++++++++++++++++++++++++++-----
> 1 file changed, 42 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/clk/at91/clk-generated.c b/drivers/clk/at91/clk-generated.c
> index 6530a2e7e84d..87866786a6ab 100644
> --- a/drivers/clk/at91/clk-generated.c
> +++ b/drivers/clk/at91/clk-generated.c
> @@ -26,6 +26,13 @@
> #define GENERATED_SOURCE_MAX 6
> #define GENERATED_MAX_DIV 255
>
> +#define GCK_ID_SSC0 43
> +#define GCK_ID_SSC1 44
> +#define GCK_ID_I2S0 54
> +#define GCK_ID_I2S1 55
> +#define GCK_ID_CLASSD 59
> +#define GCK_INDEX_DT_AUDIO_PLL 5

hum...

> +
> struct clk_generated {
> struct clk_hw hw;
> struct regmap *regmap;
> @@ -126,15 +133,14 @@ 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 +156,40 @@ 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,
> + * with the rate locking, the first consumer to enable to clock will be
> + * the one definitely setting the rate of the clock.
> + * Since audio IPs are most likely to request the same rate, we enforce
> + * that the only clks able to modify gck rate are those of audio IPs.
> + */
> +
> + if (gck->id != GCK_ID_SSC0 && gck->id != GCK_ID_SSC1 &&
> + gck->id != GCK_ID_I2S0 && gck->id != GCK_ID_I2S1 &&
> + gck->id != GCK_ID_CLASSD)
> + goto end;

...well... maybe for a temporary solution, but what about the next
product that will also have such feature but without the same set of IDs?

I know that the main use of this clock is the "audio" subsystem (so its
name) but in a machine without audio needs, it can be interesting to use
this fractional PLL for other devices that can handle a GCK (and I'm
thinking about the SDHCI interface that then could be configured with
maximum clock speed).

> + parent = clk_hw_get_parent_by_index(hw, GCK_INDEX_DT_AUDIO_PLL);
> + if (!parent)
> + goto end;

Here, if the audio pll id changes in the DT, we don't retrieve the
proper parent... And again, not very future proof.

> + 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 +299,8 @@ 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;
>

--
Nicolas Ferre