linux-kernel - Re: [PATCH v3 5/6] ARM: pinctrl: Add Broadcom Capri pinctrl driver

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Message-ID: <52B4FD8E.1010009@broadcom.com>
Date:	Fri, 20 Dec 2013 18:31:42 -0800
From:	Sherman Yin <syin@...adcom.com>
To:	Linus Walleij <linus.walleij@...aro.org>,
	Mark Brown <broonie@...nel.org>
CC:	Mark Rutland <mark.rutland@....com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Christian Daudt <bcm@...thebug.org>,
	Russell King <linux@....linux.org.uk>,
	Heiko Stübner <heiko@...ech.de>,
	Pawel Moll <pawel.moll@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Stephen Warren <swarren@...dotorg.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Rob Herring <rob.herring@...xeda.com>,
	bcm-kernel-feedback-list <bcm-kernel-feedback-list@...adcom.com>,
	Rob Landley <rob@...dley.net>,
	Grant Likely <grant.likely@...aro.org>,
	Matt Porter <matt.porter@...aro.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v3 5/6] ARM: pinctrl: Add Broadcom Capri pinctrl driver

On 13-12-18 03:56 PM, Sherman Yin wrote:
> On 13-12-12 12:54 PM, Linus Walleij wrote:

>>> +/*
>>> + * Write to the register using the value and mask if current value
>>> is different
>>> + */
>>> +static void capri_reg_write(struct pinctrl_dev *pctldev,
>>> +                           void __iomem *reg,
>>> +                           u32 val,
>>> +                           u32 mask)
>>> +{
>>> +       u32 old_val;
>>> +       u32 new_val;
>>> +
>>> +       old_val = readl(reg);
>>> +       new_val = (old_val & ~mask) | (val & mask);
>>> +
>>> +       if (new_val == old_val) {
>>> +               dev_dbg(pctldev->dev,
>>> +                       "Reg 0x%p=0x%x (no change)\n",
>>> +                       reg, old_val);
>>> +               return;
>>> +       }
>>> +
>>> +       dev_dbg(pctldev->dev,
>>> +               "Reg 0x%p change from 0x%x to 0x%x\n",
>>> +               reg, old_val, new_val);
>>> +       writel(new_val, reg);
>>> +}
>>
>> This is a reimplementation of regmap for MMIO.
>> See drivers/base/regmap/regmap-mmio.c
>> Notice how regmap_update_bits() is used throughout the
>> kernel.
>>
>> If you want to do this, use regmap.
>
> Ok.

As you can see in v4 of my patchset, I've changed my driver to use the 
mmio regmap.  However, as I was tracing through regmap_update_bits(), it 
looks like I have to go through a lot of checks and function pointers 
just to do a simple write to a register.  Also, I have to select 
REGMAP_MMIO which brings in a bunch of code as well.

I understand the benefits of using common code, but in this case it 
seems there is a lot of extra code and run-time overhead to use regmap. 
  In the end it also doesn't buy much in terms of functionality.

Just a quick note - it looks like the 2nd parameter of 
regmap_update_bits() wants the offset of a register (offset from 
regmap_mmio_context.regs).  So calling the parameter "reg" is a little 
confusing, at least in the MMIO case.

Regards,
Sherman
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