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

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;