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Subject: Re: [PATCH v3] clk: starfive: pll: Fix lower rate of CPUfreq by
 setting PLL0 rate to 1.5GHz
To: Krzysztof Kozlowski <krzk@kernel.org>,
 Xingyu Wu <xingyu.wu@starfivetech.com>,
 Michael Turquette <mturquette@baylibre.com>, Stephen Boyd
 <sboyd@kernel.org>, Conor Dooley <conor@kernel.org>,
 Emil Renner Berthing <emil.renner.berthing@canonical.com>,
 Rob Herring <robh@kernel.org>,
 Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>
Cc: Paul Walmsley <paul.walmsley@sifive.com>,
 Palmer Dabbelt <palmer@dabbelt.com>, Albert Ou <aou@eecs.berkeley.edu>,
 Hal Feng <hal.feng@starfivetech.com>, linux-kernel@vger.kernel.org,
 linux-clk@vger.kernel.org, linux-riscv@lists.infradead.org,
 devicetree@vger.kernel.org
References: <20240402090920.11627-1-xingyu.wu@starfivetech.com>
 <8d21b1bc-9402-41d4-bd81-c521c8a33d2d@kernel.org>
From: Bo Gan <ganboing@gmail.com>
Message-ID: <7e363fb9-5dff-b8de-fd4f-54b3596ad179@gmail.com>
Date: Tue, 2 Apr 2024 17:26:54 -0700
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On 4/2/24 9:18 AM, Krzysztof Kozlowski wrote:
> On 02/04/2024 11:09, Xingyu Wu wrote:
>> CPUfreq supports 4 cpu frequency loads on 375/500/750/1500MHz.
>> But now PLL0 rate is 1GHz and the cpu frequency loads become
>> 333/500/500/1000MHz in fact.
>>
>> So PLL0 rate should be default set to 1.5GHz. But setting the
>> PLL0 rate need certain steps:
>>
>> 1. Change the parent of cpu_root clock to OSC clock.
>> 2. Change the divider of cpu_core if PLL0 rate is higher than
>>     1.25GHz before CPUfreq boot.
>> 3. Change the parent of cpu_root clock back to PLL0 clock.
>>
>> Reviewed-by: Hal Feng <hal.feng@starfivetech.com>
>> Fixes: e2c510d6d630 ("riscv: dts: starfive: Add cpu scaling for JH7110 SoC")
>> Signed-off-by: Xingyu Wu <xingyu.wu@starfivetech.com>
>> ---
>>
>> Hi Stephen and Emil,
>>
>> This patch fixes the issue about lower rate of CPUfreq[1] by setting PLL0
>> rate to 1.5GHz.
>>
>> In order not to affect the cpu operation, setting the PLL0 rate need
>> certain steps. The cpu_root's parent clock should be changed first. And
>> the divider of the cpu_core clock should be set to 2 so they won't crash
>> when setting 1.5GHz without voltage regulation. Due to PLL driver boot
>> earlier than SYSCRG driver, cpu_core and cpu_root clocks are using by
>> ioremap().
>>
>> [1]: https://github.com/starfive-tech/VisionFive2/issues/55
>>
>> Previous patch link:
>> v2: https://lore.kernel.org/all/20230821152915.208366-1-xingyu.wu@starfivetech.com/
>> v1: https://lore.kernel.org/all/20230811033631.160912-1-xingyu.wu@starfivetech.com/
>>
>> Thanks,
>> Xingyu Wu
>> ---
>>   .../jh7110-starfive-visionfive-2.dtsi         |   5 +
>>   .../clk/starfive/clk-starfive-jh7110-pll.c    | 102 ++++++++++++++++++
> 
> Please do not mix DTS and driver code. That's not really portable. DTS
> is being exported and used in other projects.
> 
> ...
> 
>>   
>> @@ -458,6 +535,8 @@ static int jh7110_pll_probe(struct platform_device *pdev)
>>   	struct jh7110_pll_priv *priv;
>>   	unsigned int idx;
>>   	int ret;
>> +	struct device_node *np;
>> +	struct resource res;
>>   
>>   	priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
>>   	if (!priv)
>> @@ -489,6 +568,29 @@ static int jh7110_pll_probe(struct platform_device *pdev)
>>   			return ret;
>>   	}
>>   
>> +	priv->is_first_set = true;
>> +	np = of_find_compatible_node(NULL, NULL, "starfive,jh7110-syscrg");
> 
> Your drivers should not do it. It's fragile, hides true link/dependency.
> Please use phandles.
> 
> 
>> +	if (!np) {
>> +		ret = PTR_ERR(np);
>> +		dev_err(priv->dev, "failed to get syscrg node\n");
>> +		goto np_put;
>> +	}
>> +
>> +	ret = of_address_to_resource(np, 0, &res);
>> +	if (ret) {
>> +		dev_err(priv->dev, "failed to get syscrg resource\n");
>> +		goto np_put;
>> +	}
>> +
>> +	priv->syscrg_base = ioremap(res.start, resource_size(&res));
>> +	if (!priv->syscrg_base)
>> +		ret = -ENOMEM;
> 
> Why are you mapping other device's IO? How are you going to ensure
> synced access to registers?
> 
> 
> 
> Best regards,
> Krzysztof
> 
> 
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> 

Hi Xingyu,

Echoing Krzysztof's point. This piece code seems wrong to me. This logic belongs
to syscrg, rather than pll. Why don't you do the pll0->osc->pll0 switching from
syscrg side during probing?

Bo