linux-kernel - Re: [PATCH v10 2/2] Add PWM fan controller driver for LGM SoC

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Date:   Mon, 24 Aug 2020 17:36:47 +0800
From:   "Tanwar, Rahul" <rahul.tanwar@...ux.intel.com>
To:     Andy Shevchenko <andriy.shevchenko@...el.com>
Cc:     u.kleine-koenig@...gutronix.de, linux-pwm@...r.kernel.org,
        lee.jones@...aro.org, thierry.reding@...il.com,
        p.zabel@...gutronix.de, robh+dt@...nel.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        songjun.Wu@...el.com, cheol.yong.kim@...el.com,
        qi-ming.wu@...el.com, rahul.tanwar.linux@...il.com,
        rtanwar@...linear.com
Subject: Re: [PATCH v10 2/2] Add PWM fan controller driver for LGM SoC


Hi Andy,

On 24/8/2020 4:17 pm, Andy Shevchenko wrote:
> On Mon, Aug 24, 2020 at 11:36:37AM +0800, Rahul Tanwar wrote:
>> Intel Lightning Mountain(LGM) SoC contains a PWM fan controller.
>> This PWM controller does not have any other consumer, it is a
>> dedicated PWM controller for fan attached to the system. Add
>> driver for this PWM fan controller.
> ...
>
>> +	pc->regmap = devm_regmap_init_mmio(dev, io_base, &lgm_pwm_regmap_config);
>> +	if (IS_ERR(pc->regmap)) {
>> +		ret = PTR_ERR(pc->regmap);
>> +		if (ret != -EPROBE_DEFER)
>> +			dev_err_probe(dev, ret, "failed to init register map\n");
>> +		return ret;
>> +	}
>> +
>> +	pc->clk = devm_clk_get(dev, NULL);
>> +	if (IS_ERR(pc->clk)) {
>> +		ret = PTR_ERR(pc->clk);
>> +		if (ret != -EPROBE_DEFER)
>> +			dev_err_probe(dev, ret, "failed to get clock\n");
>> +		return ret;
>> +	}
>> +
>> +	pc->rst = devm_reset_control_get_exclusive(dev, NULL);
>> +	if (IS_ERR(pc->rst)) {
>> +		ret = PTR_ERR(pc->rst);
>> +		if (ret != -EPROBE_DEFER)
>> +			dev_err_probe(dev, ret, "failed to get reset control\n");
>> +		return ret;
>> +	}
>> +
>> +	ret = reset_control_deassert(pc->rst);
>> +	if (ret) {
>> +		if (ret != -EPROBE_DEFER)
>> +			dev_err_probe(dev, ret, "cannot deassert reset control\n");
>> +		return ret;
>> +	}
> Please, spend a bit of time to understand the changes you are doing. There are
> already few examples how to use dev_err_probe() properly.

I guess your point is that the check of (ret !- -EPROBE_DEFER) is not needed
when using dev_err_probe() as it encapsulates it. Sorry, i missed it. Will
fix it. I am not able to find any other missing point after referring to
two driver examples which uses dev_err_probe() ?

>> +	ret = clk_prepare_enable(pc->clk);
>> +	if (ret) {
>> +		dev_err(dev, "failed to enable clock\n");
>> +		return ret;
>> +	}
>> +
>> +	ret = devm_add_action_or_reset(dev, lgm_pwm_action, pc);
>> +	if (ret)
>> +		return ret;
> You have also ordering issues here.
>
> So, what I can see about implementation is that
>
>
> 	static void ..._clk_disable(void *data)
> 	{
> 		clk_disable_unprepare(data);
> 	}
>
> 	static int ..._clk_enable(...)
> 	{
> 		int ret;
>
> 		ret = clk_preare_enable(...);
> 		if (ret)
> 			return ret;
> 		return devm_add_action_or_reset(..., ..._clk_disable);
> 	}
>
>
> Similar for reset control.
>
> Then in the ->probe() something like this:
>
> 	ret = devm_reset_control_get...;
> 	if (ret)
> 		return ret;
>
> 	ret = ..._reset_deassert(...);
> 	if (ret)
> 		return ret;
>
> followed by similar section for the clock.
>

Regarding ordering: In early rounds of review, feedback about ordering was that
it is recommended to be reverse of the sequence in probe i.e.
if in probe:
1. reset_control_deassert()
2. clk_prepare_enable()
then in remove:
1. clk_disable_uprepare()
2. reset_control_assert()

That's the reason i added a generic action() which reverses order.

I understand your suggested way as explained above but not sure if that would
ensure reverse ordering during unwind.

Thanks.

Regards,
Rahul