linux-kernel - Re: [PATCH 0/6] arm64: dts: freescale: imx8mp-skov: switch to nominal drive mode

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Message-ID: <44278a64-7578-4109-aef3-4888627166d1@pengutronix.de>
Date: Fri, 20 Dec 2024 07:21:36 +0100
From: Ahmad Fatoum <a.fatoum@...gutronix.de>
To: Peng Fan <peng.fan@....nxp.com>
Cc: Abel Vesa <abelvesa@...nel.org>, Peng Fan <peng.fan@....com>,
 Michael Turquette <mturquette@...libre.com>, Stephen Boyd
 <sboyd@...nel.org>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Shawn Guo <shawnguo@...nel.org>,
 Sascha Hauer <s.hauer@...gutronix.de>,
 Pengutronix Kernel Team <kernel@...gutronix.de>,
 Fabio Estevam <festevam@...il.com>, Abel Vesa <abel.vesa@...aro.org>,
 Marek Vasut <marex@...x.de>, linux-clk@...r.kernel.org, imx@...ts.linux.dev,
 devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/6] arm64: dts: freescale: imx8mp-skov: switch to nominal
 drive mode

Hello Peng,

On 20.12.24 07:16, Peng Fan wrote:
> On Thu, Dec 19, 2024 at 08:27:31AM +0100, Ahmad Fatoum wrote:
>> Unlike the i.MX8MM and i.MX8MN SoCs added earlier, the imx8mp.dtsi
>> configures some clocks at frequencies that are only validated for
>> overdrive mode, i.e., when VDD_SOC is 950 mV.
>>
>> For the Skov i.MX8MP board, we want to run the SoC at the lower voltage of
>> 850 mV though to reduce heat generation and power usage. For this to work,
>> clock rates need to adhere to the limits of the nominal drive mode.
>>
>> This is done by this series: A new imx8mp-nominal.dtsi reconfigures
>> the imx8mp.dtsi clock tree to be compatible with nominal mode, an adaptation
>> to the Linux clock driver makes it sanity check the actual clock rates against
>> the SoC operating mode's constraints and finally the Skov DT makes use
>> of it.
>>
>> Actual configuration of the VDD_SOC rail continues to happen prior to Linux
>> as well as PLL configuration that needs to happen earlier than the kernel
>> running. See the corresponding barebox patch series[1] for details.
>> Note that the barebox series didn't yet include VDD_SOC reconfiguration
>> to 850mV, that would follow once the kernel changes have been merged.
> 
> Good to see this. I had same plan to support i.MX9.
> 
> I see you introduce a new property, how about using a boot pararmeter,
> saying "mode=nominal" or "mode=overdrive". Then drivers could
> act accordingly.

I assume you would place that parameter in drivers/soc/imx/soc-imx8m.c?

That's certainly possible as well, but I think for such a hardware property,
the device tree is the natural place.

Thanks,
Ahmad

> 
> Regards,
> Peng
> 
>>
>> [1]: https://lore.kernel.org/barebox/20240503103717.1370636-1-a.fatoum@pengutronix.de/
>>
>> ---
>> Ahmad Fatoum (6):
>>      dt-bindings: clock: imx8m: document nominal/overdrive properties
>>      arm64: dts: imx8mp: Add optional nominal drive mode DTSI
>>      arm64: dts: imx8mp: add fsl,nominal-mode property into nominal.dtsi
>>      arm64: dts: freescale: imx8mp-skov: fix LDB clock rate configuration
>>      arm64: dts: freescale: imx8mp-skov: operate SoC in nominal mode
>>      clk: imx8mp: inform CCF of maximum frequency of clocks
>>
>> .../devicetree/bindings/clock/imx8m-clock.yaml     |  14 ++
>> arch/arm64/boot/dts/freescale/imx8mp-nominal.dtsi  |  64 +++++++++
>> .../arm64/boot/dts/freescale/imx8mp-skov-reva.dtsi |   5 +-
>> .../freescale/imx8mp-skov-revb-mi1010ait-1cp1.dts  |  19 +--
>> drivers/clk/imx/clk-imx8mp.c                       | 147 +++++++++++++++++++++
>> 5 files changed, 233 insertions(+), 16 deletions(-)
>> ---
>> base-commit: 78d4f34e2115b517bcbfe7ec0d018bbbb6f9b0b8
>> change-id: 20241217-imx8m-clk-9467763dfcd8
>>
>> Best regards,
>> -- 
>> Ahmad Fatoum <a.fatoum@...gutronix.de>
>>
> 


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