Hi Peng,

On 20.12.24 07:18, Peng Fan wrote:

On Thu, Dec 19, 2024 at 08:27:37AM +0100, Ahmad Fatoum wrote:

quoted

The IMX8MPCEC datasheet lists maximum frequencies allowed for different
modules. Some of these limits are universal, but some depend on
whether the SoC is operating in nominal or in overdrive mode.

The imx8mp.dtsi currently assumes overdrive mode and configures some
clocks in accordance with this. Boards wishing to make use of nominal
mode will need to override some of the clock rates manually.

As operating the clocks outside of their allowed range can lead to
difficult to debug issues, it makes sense to register the maximum rates
allowed in the driver, so the CCF can take them into account.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>

quoted

+	imx8mp_clocks_apply_constraints(imx8mp_clock_common_constraints);
+
+	if (of_property_read_bool(np, "fsl,nominal-mode"))
+		imx8mp_clocks_apply_constraints(imx8mp_clock_nominal_constraints);
+	else if (of_property_read_bool(np, "fsl,overdrive-mode"))
+		imx8mp_clocks_apply_constraints(imx8mp_clock_overdrive_constraints);

As I replied, a boot parameter should be better? the mode is a soc level mode,
not just clock controller.

I think it's counterproductive for a sanity check to be enforced via kernel
command-line.

The Skov board shouldn't run with overdrive frequencies and I prefer to encode
that in the same device tree, where I define the permissible VDD_SOC range
and configure the initial clock rates.

The mode is selected by the VDD_SOC voltage, but affects AFAICS only the clock
tree. IMO, the clock controller module is thus a natural place for the property.

Cheers,
Ahmad

Thanks,
Peng

quoted

+
	err = of_clk_add_hw_provider(np, of_clk_hw_onecell_get, clk_hw_data);
	if (err < 0) {
		dev_err(dev, "failed to register hws for i.MX8MP\n");

-- 
2.39.5

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