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Date: Wed, 15 Oct 2014 16:32:39 +0300 From: Octavian Purdila <octavian.purdila@...el.com> To: Guenter Roeck <linux@...ck-us.net> 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 Wed, Oct 15, 2014 at 4:13 PM, Guenter Roeck <linux@...ck-us.net> wrote: > 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 ? > Here is how sysfs uses is_visible: static int create_files(struct kernfs_node *parent, struct kobject *kobj, ... if (grp->is_visible) { mode = grp->is_visible(kobj, *attr, i); if (!mode) continue; } error = sysfs_add_file_mode_ns(parent, *attr, false, (*attr)->mode | mode, NULL); so basically is the mode set is the original mode from the attributed "or-ed" with the mode return by is_visible. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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