linux-kernel - Re: [PATCH v13 2/2] Add PWM fan controller driver for LGM SoC

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Date:   Thu, 24 Sep 2020 16:16:59 +0200
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     Andy Shevchenko <andriy.shevchenko@...el.com>
Cc:     Rahul Tanwar <rahul.tanwar@...ux.intel.com>,
        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 v13 2/2] Add PWM fan controller driver for LGM SoC

On Thu, Sep 24, 2020 at 04:23:34PM +0300, Andy Shevchenko wrote:
> On Thu, Sep 24, 2020 at 08:55:34AM +0200, Uwe Kleine-König wrote:
> > On Tue, Sep 15, 2020 at 04:23:37PM +0800, Rahul Tanwar wrote:
> 
> ...
> 
> > > +	ret = lgm_clk_enable(dev, pc);
> > > +	if (ret) {
> > > +		dev_err(dev, "failed to enable clock\n");
> > 
> > You used dev_err_probe four times for six error paths. I wonder why you
> > didn't use it here (and below for a failing pwmchip_add()).
> 
> dev_err_probe() makes sense when we might experience deferred probe. In neither
> of mentioned function this can be the case.
> 
> > > +		return ret;
> > > +	}
> 
> ...
> 
> > > +	ret = lgm_reset_control_deassert(dev, pc);
> > > +	if (ret)
> > > +		return dev_err_probe(dev, ret, "cannot deassert reset control\n");
> > 
> > After lgm_reset_control_deassert is called pc->rst is unused. So there
> > is no need to have this member in struct lgm_pwm_chip. The same applies
> > to ->clk. (You have to pass rst (or clk) to devm_add_action_or_reset for
> > that to work. Looks like a nice idea anyhow.)
> 
> True. And above dev_err_probe() is not needed.

You argue that dev_err_probe() gives no benefit as
lgm_reset_control_deassert won't return -EPROBE_DEFER, right?

Still I consider it a useful function because

 a) I (as an author or as a reviewer) don't need to think if the
    failing function might return -EPROBE_DEFER now or in the future.
    dev_err_probe does the right thing even for functions that don't
    return -EPROBE_DEFER.

 b) With dev_err_probe() I can accomplish things in a single line that
    need two lines when open coding it.

 c) dev_err_probe() emits the symbolic error name without having to
    resort to %pe + ERR_PTR.

 d) Using dev_err_probe() for all error paths gives a consistency that I
    like with a maintainer's hat on.

So I still want to request using dev_err_probe() in all error paths.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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