linux-kernel - Re: [PATCH v3] clk: starfive: pll: Fix lower rate of CPUfreq by setting PLL0 rate to 1.5GHz

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Message-ID: <bcf12c0b-d569-4d64-adfb-bad053c182a8@kernel.org>
Date: Wed, 3 Apr 2024 09:23:33 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Xingyu Wu <xingyu.wu@...rfivetech.com>,
 Michael Turquette <mturquette@...libre.com>, Stephen Boyd
 <sboyd@...nel.org>, Conor Dooley <conor@...nel.org>,
 Emil Renner Berthing <emil.renner.berthing@...onical.com>,
 Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>
Cc: Paul Walmsley <paul.walmsley@...ive.com>,
 Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>,
 Hal Feng <hal.feng@...rfivetech.com>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "linux-clk@...r.kernel.org" <linux-clk@...r.kernel.org>,
 "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
 "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [PATCH v3] clk: starfive: pll: Fix lower rate of CPUfreq by
 setting PLL0 rate to 1.5GHz

On 03/04/2024 09:19, Xingyu Wu wrote:
> On 03/04/2024 0:18, 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@...rfivetech.com>
>>> Fixes: e2c510d6d630 ("riscv: dts: starfive: Add cpu scaling for JH7110
>>> SoC")
>>> Signed-off-by: Xingyu Wu <xingyu.wu@...rfivetech.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@starfive
>>> tech.com/
>>> v1:
>>> https://lore.kernel.org/all/20230811033631.160912-1-xingyu.wu@starfive
>>> tech.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.
> 
> OK, I will submit that in two patches.
> 
>>
>> ...
>>
>>>
>>> @@ -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?
> 
> Because setting PLL0 rate need specific steps and use the clocks of SYSCRG.

That's not a reason to map other device's IO. That could be a reason for
having syscon or some other sort of relationship, like clock or reset.

> But SYSCRG driver also need PLL clock to be clock source when adding clock
> providers. I tried to add SYSCRG clocks in 'clocks' property in DT and use
> clk_get() to get the clocks. But it could not run and crash. So I use ioremap()
> instead.

So instead of properly model the relationship, you entangle the drivers
even more.

Please come with a proper design for this. I have no clue about your
hardware, but that looks like you are asynchronously configuring the
same hardware in two different places.

Sorry, that's poor code.

Best regards,
Krzysztof