linux-kernel - Re: [PATCH v2 6/9] mfd: max77714: Add driver for Maxim MAX77714 PMIC

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Date:   Wed, 27 Oct 2021 14:44:30 +0100
From:   Lee Jones <lee.jones@...aro.org>
To:     Luca Ceresoli <luca@...aceresoli.net>
Cc:     linux-kernel@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
        Alessandro Zummo <a.zummo@...ertech.it>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>,
        Guenter Roeck <linux@...ck-us.net>, devicetree@...r.kernel.org,
        linux-rtc@...r.kernel.org, linux-watchdog@...r.kernel.org,
        Chiwoong Byun <woong.byun@...sung.com>,
        Laxman Dewangan <ldewangan@...dia.com>,
        Randy Dunlap <rdunlap@...radead.org>
Subject: Re: [PATCH v2 6/9] mfd: max77714: Add driver for Maxim MAX77714 PMIC

On Wed, 27 Oct 2021, Luca Ceresoli wrote:

> Hi Lee,
> 
> On 21/10/21 20:43, Lee Jones wrote:
> > On Tue, 19 Oct 2021, Luca Ceresoli wrote:
> [...]
> >> diff --git a/drivers/mfd/max77714.c b/drivers/mfd/max77714.c
> >> new file mode 100644
> >> index 000000000000..4b49d16fe199
> >> --- /dev/null
> >> +++ b/drivers/mfd/max77714.c
> >> @@ -0,0 +1,165 @@
> >> +// SPDX-License-Identifier: GPL-2.0-only
> >> +/*
> >> + * Maxim MAX77714 MFD Driver
> >> + *
> >> + * Copyright (C) 2021 Luca Ceresoli
> >> + * Author: Luca Ceresoli <luca@...aceresoli.net>
> >> + */
> >> +
> >> +#include <linux/i2c.h>
> >> +#include <linux/interrupt.h>
> >> +#include <linux/mfd/core.h>
> >> +#include <linux/mfd/max77714.h>
> >> +#include <linux/module.h>
> >> +#include <linux/of.h>
> >> +#include <linux/regmap.h>
> >> +
> >> +struct max77714 {
> >> +	struct device *dev;
> >> +	struct regmap *regmap;
> >> +	struct regmap_irq_chip_data *irq_data;
> > 
> > Is this used outside of .probe()?
> 
> No.

Then you don't need to store it in a struct.

[...]

> >> +	/* Internal Crystal Load Capacitance, indexed by value of 32KLOAD bits */
> >> +	static const unsigned int load_cap[4] = {0, 10, 12, 22};
> > 
> > Probably best to define these magic numbers.
> 
> Since these numbers do not appear anywhere else I don't find added value in:
> 
>   #define MAX77714_LOAD_CAP_0   0
>   #define MAX77714_LOAD_CAP_10  10
>   #define MAX77714_LOAD_CAP_12  12
>   #define MAX77714_LOAD_CAP_22  22
>   [...]
>   static const unsigned int load_cap[4] = {
>       MAX77714_LOAD_CAP_0,
>       MAX77714_LOAD_CAP_10,
>       MAX77714_LOAD_CAP_12,
>       MAX77714_LOAD_CAP_12,
>   };

I don't find value in that nomenclature either! :)

I was suggesting that you used better, more forthcoming names.

 LOAD_CAPACITANCE_00_pF
 LOAD_CAPACITANCE_10_pF
 LOAD_CAPACITANCE_12_pF
 LOAD_CAPACITANCE_22_pF

> besides adding lots of lines and lots of "MAX77714_LOAD_CAP_". Even
> worse, there is potential for copy-paste errors -- can you spot it? ;)

Yes.  Straight away.

> Finally, consider this is not even global but local to a small function.
> 
> But I'd rather add the unit ("pF") to either the comment line of the
> array name (load_cap -> load_cap_pf) for clarity. Would that be OK for you?

I did have to read the code again to get a handle on things (probably
not a good sign).  To keep things simple, just add "/* pF */" onto the
end of the load_cap line for now.  That should clear things up at
first glance.

-- 
Lee Jones [李琼斯]
Senior Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
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