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Subject: Re: [MeeGo-Dev][PATCH] Topcliff: Update PCH_I2C driver to 2.6.35
From: Joe Perches <joe@perches.com>
To: Masayuki Ohtake <masa-korg@dsn.okisemi.com>
Cc: "Jean Delvare (PC drivers, core)" <khali@linux-fr.org>,
        "Ben Dooks (embedded platforms)" <ben-linux@fluff.org>,
        Crane Cai <crane.cai@amd.com>, Samuel Ortiz <sameo@linux.intel.com>,
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        Ralf Baechle <ralf@linux-mips.org>,
        srinidhi kasagar <srinidhi.kasagar@stericsson.com>,
        linux-i2c@vger.kernel.org, linux-kernel@vger.kernel.org,
        "Wang Yong Y\"" <yong.y.wang@intel.com>,
        "Wang Qi\"" <qi.wang@intel.com>,
        "Andrew\"" <andrew.chih.howe.khor@intel.com>, arjan@linux.intel.com,
        Tomoya MORINAGA <morinaga526@dsn.okisemi.com>,
        Arnd Bergmann <arnd@arndb.de>
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Date: Tue, 31 Aug 2010 22:24:14 -0700
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On Wed, 2010-09-01 at 14:08 +0900, Masayuki Ohtake wrote:
> I have a question.
> Current our I2C driver  has the following 2 patterns dev_err().
> (1) dev_err(adap->pch_adapter.dev.parent, "...");
> (2) dev_err(&pdev->dev, "...");
> > #define pch_err(adap, fmt, arg...) \
> > dev_err(adap->pch_adapter.dev.parent, fmt, ##arg)
> In case of using the above code, pattern (1) can apply, but (2) can't.
> As to (2),
> Should we use as dev_err or define another macro?

Hello Ohtake.

To me, it's a visual complexity vs std pattern trade-off.

A 2 level dereference like dev_info(&dev->dev, ...)
isn't overly difficult to read.
3 or more dereferences can be harder and a bit error prone.
So I would only use pch_<level> for (1) and dev_err for (2).

There are also times when there are additional standard
arguments that you want to prefix to dev_<level> calls
and that can be simplified with a custom XXX_<level>
define for dev_<level>

Look at the current uses in the tree and see what you like.

$ grep -rP --include=*.[ch] "#define\s*.+\s+dev_[a-z]{3,7}\s*\(" *

These aren't requirements, do what you think best.

cheers, Joe