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

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Date:   Mon, 24 Aug 2020 13:14:54 +0300
From:   Andy Shevchenko <andriy.shevchenko@...el.com>
To:     "Tanwar, Rahul" <rahul.tanwar@...ux.intel.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

On Mon, Aug 24, 2020 at 05:36:47PM +0800, Tanwar, Rahul wrote:
> On 24/8/2020 4:17 pm, Andy Shevchenko wrote:
> > On Mon, Aug 24, 2020 at 11:36:37AM +0800, Rahul Tanwar wrote:

...

> >> +	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.

It does even more. Look at the existing examples.

> 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() ?

There are three drivers that are using it in Linux Next. All of them utilizing
it correctly, look at them.

> >> +	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.

Yes, and my suggestion follows this.

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

You have:
 devm r1
 devm r2
 enable r1
 enable r2 (and here you have broken error path)

My suggestion has it like this (and no broken error path):
 devm r1
 enable r1
 devm r2
 enable r2

-- 
With Best Regards,
Andy Shevchenko