Hello Conor, On 19.12.24 20:49, Conor Dooley wrote: > On Thu, Dec 19, 2024 at 08:27:32AM +0100, Ahmad Fatoum wrote: >> The imx8m-clock.yaml binding covers the clock controller inside all >> of the i.MX8M Q/M/N/P SoCs. All of them have in common that they >> support two operating modes: nominal and overdrive mode. > > This implies that only the two modes you mention are possible, but you > leave the option open to a dts author to use either. How come? > > Makes it seem like we only need one of these, for whatever the > non-default option is? There is no real default. The mode is configured implicitly by the bootloader setting VDD_SOC and then kernel needs to adhere to the limits that imposes. For i.MX8M Mini and Nano, the kernel SoC DTSIs has assigned-clock-rates that are all achievable in nominal mode. For i.MX8MP, there are some rates only validated for overdrive mode. But even for the i.MX8M Mini/Nano boards, we don't know what rates they may configure at runtime, so it's not possible to infer from just the device tree what the mode is, which is why I need to allow for absence of either property. I can make it a single property with two possible values though if that's preferable. Theoretically, we could infer mode at runtime from VDD_SOC voltage, but we need to set up clocks to read out the PMIC and I want to apply the constraints as early as possible as I don't want the SoC to run outside of spec even for a short while. Thanks, Ahmad > >> >> While the overdrive mode allows for higher frequencies for many IPs, >> the nominal mode needs a lower SoC voltage, thereby reducing >> heat generation and power usage. >> >> In any case, software should respect the maximum clock rate limits >> described in the datasheet for each of the two operating modes. >> >> To allow device tree consumers to enforce these limits, document two new >> optional properties that can be used to sanity check the clock tree. >> >> Signed-off-by: Ahmad Fatoum <a.fatoum@xxxxxxxxxxxxxx> >> --- >> Documentation/devicetree/bindings/clock/imx8m-clock.yaml | 14 ++++++++++++++ >> 1 file changed, 14 insertions(+) >> >> diff --git a/Documentation/devicetree/bindings/clock/imx8m-clock.yaml b/Documentation/devicetree/bindings/clock/imx8m-clock.yaml >> index c643d4a81478..a6ae5257ef53 100644 >> --- a/Documentation/devicetree/bindings/clock/imx8m-clock.yaml >> +++ b/Documentation/devicetree/bindings/clock/imx8m-clock.yaml >> @@ -43,6 +43,14 @@ properties: >> ID in its "clocks" phandle cell. See include/dt-bindings/clock/imx8m-clock.h >> for the full list of i.MX8M clock IDs. >> >> + fsl,nominal-mode: >> + description: Set if SoC is operated in nominal mode >> + $ref: /schemas/types.yaml#/definitions/flag >> + >> + fsl,overdrive-mode: >> + description: Set if SoC is operated in overdrive mode >> + $ref: /schemas/types.yaml#/definitions/flag >> + >> required: >> - compatible >> - reg >> @@ -95,6 +103,12 @@ allOf: >> - const: clk_ext2 >> - const: clk_ext3 >> - const: clk_ext4 >> + - if: >> + required: >> + - fsl,overdrive-mode >> + then: >> + properties: >> + fsl,nominal-mode: false >> >> additionalProperties: false >> >> >> -- >> 2.39.5 >> -- Pengutronix e.K. | | Steuerwalder Str. 21 | http://www.pengutronix.de/ | 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
