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

[Guenter Roeck <linux-0h96xk9xTtrk1uMJSBkQmQ@public.gmane.org>]

On 10/15/2014 04:49 AM, Octavian Purdila wrote:
> On Tue, Oct 14, 2014 at 6:41 PM, Guenter Roeck <linux-0h96xk9xTtrk1uMJSBkQmQ@public.gmane.org> 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