linux-kernel - Re: [PATCH v4] cpuidle: sunplus: Create cpuidle driver for sunplus sp7021

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Message-ID: <136f2087-10e7-c9e8-2292-3046711c8f68@canonical.com>
Date:   Mon, 14 Feb 2022 07:44:30 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>
To:     Edwin Chiu 邱垂峰 <edwin.chiu@...plus.com>,
        Edwin Chiu <edwinchiu0505tw@...il.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "rafael@...nel.org" <rafael@...nel.org>,
        "daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>
Subject: Re: [PATCH v4] cpuidle: sunplus: Create cpuidle driver for sunplus
 sp7021

On 14/02/2022 03:55, Edwin Chiu 邱垂峰 wrote:
> Hi Krzysztof:
> 
> Please see below answer.
> 
>>> +static struct cpuidle_driver sp7021_idle_driver = {
>>> +	.name = "sp7021_idle",
>>> +	.owner = THIS_MODULE,
>>> +	/*
>>> +	 * State at index 0 is standby wfi and considered standard
>>> +	 * on all ARM platforms. If in some platforms simple wfi
>>> +	 * can't be used as "state 0", DT bindings must be implemented
>>> +	 * to work around this issue and allow installing a special
>>> +	 * handler for idle state index 0.
>>> +	 */
>>> +	.states[0] = {
>>> +		.enter                  = sp7021_enter_idle_state,
>>> +		.exit_latency           = 1,
>>> +		.target_residency       = 1,
>>> +		.power_usage		= UINT_MAX,
>>> +		.name                   = "WFI",
>>> +		.desc                   = "ARM WFI",
>>
>> I have impression that there is no point in having custom driver with WFI...
>>
>> Still the main question from Daniel and Sudeep stays: why do you need this? You copied exactly
>> cpuildle-arm driver, there is nothing different here. At least I could not spot differences. Maybe except
>> that you use cpu_v7_do_idle explicitly.
>>
>> Unfortunately I cannot understand the explanation here:
>> https://lore.kernel.org/all/0812c44f777d4026b79df2e3698294be@sphcmbx02.sunplus.com.tw/
>> Why exactly cpuidle-arm does not work in your case?
>>
> Edwin=> I mean cpuidle-arm driver can't directly use with no modified.
>        If someone want to use cpuidle-arm driver, below modification seems necessary.
>        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>        Static int sp7021_cpuidle_suspend_enter(unsigned long index) {~}
>        Static int __init sp7021_cpuidle_init(struct device_node *cpu_node, int cpu) {~}
>        Static const struct cpuidle_ops sc_smp_ops __initconst = {
>             .suspend = sp7021_cpuidle_suspend_enter,
>             .init = sp7021_cpuidle_init,
>        };
>        CPUIDLE_METHOD_OF_DECLARE(sc_smp, "sunplus,sc-smp", &sc_smp_ops); //declare enable method
>        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>        
>        But change cpuilde-arm.c for sunplus driver seems not reasonable.
>        That is why I want to submit cpuidle-sunplus.c
>        Althought sunplus cpuidle only come in WFI, but it can complete the cpuidle framework.

I don't think it is correct. You can use cpuidle-arm, because it is
being always initialized with device_initcall(). You either use
appropriate compatible in DT or add your compatible to cpuidle-arm.

Even if this did not work, then the solution is to use common parts, not
to duplicate entire driver. Duplicating is not acceptable.

Best regards,
Krzysztof