On Mon, Sep 02, 2024 at 11:33:57PM GMT, Jie Luo wrote:

On 8/31/2024 6:24 AM, Stephen Boyd wrote:

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Quoting Jie Luo (2024-08-30 09:14:28)

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Hi Stephen,
Please find below a minor update to my earlier message on clk_ops usage.

Ok. Next time you can trim the reply to save me time.

OK.

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On 8/28/2024 1:44 PM, Jie Luo wrote:

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On 8/28/2024 7:50 AM, Stephen Boyd wrote:

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Quoting Luo Jie (2024-08-27 05:46:00)

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+       case 48000000:
+               val |= FIELD_PREP(CMN_PLL_REFCLK_INDEX, 7);
+               break;
+       case 50000000:
+               val |= FIELD_PREP(CMN_PLL_REFCLK_INDEX, 8);
+               break;
+       case 96000000:
+               val |= FIELD_PREP(CMN_PLL_REFCLK_INDEX, 7);
+               val &= ~CMN_PLL_REFCLK_DIV;
+               val |= FIELD_PREP(CMN_PLL_REFCLK_DIV, 2);
+               break;
+       default:
+               return -EINVAL;
+       }

Why isn't this done with struct clk_ops::set_rate() or clk_ops::init()?

OK, I will move this code into the clk_ops::init().

This code is expected to be executed once for initializing the CMN PLL
to enable output clocks, and requires the parent clock rate to be
available. However the parent clock rate is not available in the
clk_ops::init(). Hence clk_ops::set_rate() seems to be the right option
for this. Please let us know if this approach is fine. Thanks.

Sure. It actually sounds like the PLL has a mux to select different
reference clks. Is that right? If so, it seems like there should be
multiple 'clocks' for the DT property and many parents possible. If
that's the case then it should be possible to have something like

	clocks = <0>, <&refclk>, <0>;

in the DT node and then have clk_set_rate() from the consumer actually
set the parent index in hardware. If that's all static then it can be
done with assigned-clock-parents or assigned-clock-rates.

Thanks Stephen. The CMN PLL block always uses a single input reference
clock pin on any given IPQ SoC, however its rate may be different on
different IPQ SoC. For example, its rate is 48MHZ on IPQ9574 and 96MHZ
on IPQ5018.

Your second suggestion seems more apt for this device. I can define the
DT property 'assigned-clock-parents' to configure the clock parent of
CMN PLL. The code for reference clock selection will be added in
clk_ops::set_parent(). Please let us know if this approach is fine.

What is the source of this clock? Can you call clk_get_rate() on this
input?

-- 
With best wishes
Dmitry