linux-kernel - Re: [RFC PATCH v2 3/3] i2c: show and change bus frequency via sysfs

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Date:	Wed, 15 Oct 2014 06:13:54 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Octavian Purdila <octavian.purdila@...el.com>
CC:	Wolfram Sang <wsa@...-dreams.de>, Johan Hovold <johan@...nel.org>,
	linux-i2c <linux-i2c@...r.kernel.org>, linux-api@...r.kernel.org,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v2 3/3] i2c: show and change bus frequency via sysfs

On 10/15/2014 04:49 AM, Octavian Purdila wrote:
> On Tue, Oct 14, 2014 at 6:41 PM, Guenter Roeck <linux@...ck-us.net> wrote:
>>
>> On Tue, Oct 14, 2014 at 05:48:14PM +0300, Octavian Purdila wrote:
>>> This patch adds three new sysfs files: bus_frequency,
>>> bus_min_frequency and bus_max_frequency which allows the user to view
>>> or change the bus frequency on a per bus level.
>>>
>
> <snip>
>
>>> +
>>> +static DEVICE_ATTR(bus_frequency, S_IRUGO, i2c_sysfs_freq_show,
>>> +                i2c_sysfs_freq_store);
>>
>> Consider using DEVICE_ATTR_RO here. Also, extra empty line.
>>
>
> Unfortunately that won't work because we must transform bus_frequency
> to a RW entry (via is_visible) if the bus can change the frequency. We

Ah yes, you are right.

> can't use DEVIE_ATTR_RW either, because transforming a RW entry to a
> RO entry with is visible is not possible:
>

Why not ?

is_visible returns the desired mode. Just like you can return mode | S_IWUSR,
you can return mode & ~S_IWUSR.

Am I missing something ?

Guenter

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