linux-kernel - Re: [PATCH 6/6] clk: imx8mp: inform CCF of maximum frequency of clocks

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Message-ID: <22faf38d-3e64-40b8-9896-dcccefcc181a@pengutronix.de>
Date: Fri, 20 Dec 2024 07:30:28 +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 6/6] clk: imx8mp: inform CCF of maximum frequency of
 clocks

Hi Peng,

On 20.12.24 07:18, Peng Fan wrote:
> On Thu, Dec 19, 2024 at 08:27:37AM +0100, Ahmad Fatoum wrote:
>> 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@...gutronix.de>

>> +	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
> 
>> +
>> 	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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