linux-kernel - Re: [PATCH 00/34] treewide: simplify getting the adapter of an I2C client

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Date:   Sun, 9 Jun 2019 16:37:52 +0000
From:   Peter Rosin <peda@...ntia.se>
To:     Wolfram Sang <wsa+renesas@...g-engineering.com>,
        "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>
CC:     "linux-renesas-soc@...r.kernel.org" 
        <linux-renesas-soc@...r.kernel.org>,
        "devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-clk@...r.kernel.org" <linux-clk@...r.kernel.org>,
        "linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-leds@...r.kernel.org" <linux-leds@...r.kernel.org>,
        "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
        "linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "linux-rtc@...r.kernel.org" <linux-rtc@...r.kernel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>
Subject: Re: [PATCH 00/34] treewide: simplify getting the adapter of an I2C
 client

On 2019-06-08 12:55, Wolfram Sang wrote:
> While preparing a refactoring series, I noticed that some drivers use a
> complicated way of determining the adapter of a client. The easy way is
> to use the intended pointer: client->adapter
> 
> These drivers do:
> 	to_i2c_adapter(client->dev.parent);
> 
> The I2C core populates the parent pointer as:
> 	client->dev.parent = &client->adapter->dev;
> 
> Now take into consideration that
> 	to_i2c_adapter(&adapter->dev);
> 
> is a complicated way of saying 'adapter', then we can even formally
> prove that the complicated expression can be simplified by using
> client->adapter.
> 
> The conversion was done using a coccinelle script with some manual
> indentation fixes applied on top.
> 
> To avoid a brown paper bag mistake, I double checked this on a Renesas
> Salvator-XS board (R-Car M3N) and verified both expression result in the
> same pointer. Other than that, the series is only build tested.

Similar things go on in:

drivers/hwmon/lm90.c
drivers/leds/leds-is31fl319x.c
drivers/of/unittest.c

Those have this pattern:

	struct device *dev = &client->dev;
	struct i2c_adapter *adapter = to_i2c_adapter(dev->parent);

And drivers/rtc/rtc-fm3130.c has a couple of these:

	tmp = i2c_transfer(to_i2c_adapter(fm3130->client->dev.parent),
			...);

where fm3130->client is of type "struct i2c_client *"

Cheers,
Peter