On Thu, Dec 19, 2024 at 09:14:10PM +0100, Ahmad Fatoum wrote: > 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. Apologies for the delay responding to you, doing it today cos I feel guilty! I think what you've explained here is fine, but could you add a bit more of that info to the commit message, explaining why one cannot be default? With that, Acked-by: Conor Dooley <conor.dooley@xxxxxxxxxxxxx> Cheers, Conor. > > 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 |
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