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Date: Wed, 15 Oct 2014 06:46:30 -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 06:32 AM, Octavian Purdila wrote: > 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. > Ah, you are right. That's a new one for me. Thanks, I didn't notice earlier. Good to know ;-). Guenter -- 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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