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Date: Sun, 12 Oct 2014 10:06:37 -0700 From: Guenter Roeck <linux@...ck-us.net> To: Octavian Purdila <octavian.purdila@...el.com> Cc: Mark Roszko <mark.roszko@...il.com>, linux-i2c <linux-i2c@...r.kernel.org>, linux-api@...r.kernel.org, lkml <linux-kernel@...r.kernel.org>, Johan Hovold <johan@...nel.org>, Wolfram Sang <wsa@...-dreams.de> Subject: Re: [RFC PATCH 3/3] i2c: show and change bus frequency via sysfs On Sun, Oct 12, 2014 at 12:32:56PM +0300, Octavian Purdila wrote: > On Sat, Oct 11, 2014 at 11:14 PM, Mark Roszko <mark.roszko@...il.com> wrote: > > > This seems limiting to arches with peripherals that can support a range of > > frequencies rather than fixed numbers. > > Also it creates some portability quirkiness between platforms when all the > > i2c bus drivers have different supported freq lists and you have to match > > exactly the right frequency. I.e. one guy does 60khz but another only has > > 80khz. > > Sorry, I don't understand your points here. If this limitations exists > they are not introduced by this patch. This patch just exposes the > frequency so that it can be read or changed in userspace. > > > Another issue is in systems where you have i2c devices on the same bus as > > the sysfs user space driver. User space could set a bus frequency that > > prevents operation with a system i2c device. > > Changing the frequency is limited to root. Also, bus drivers do not > have to implement set_freq if it is thought not to be safe. > > On a different not, I have noticed that a fixed set of frequencies > might not be the best API, since multiple drivers rather support a > rather large set of frequencies in a range. A better API might be to > expose a min-max range and let the bus driver adjust the requested > frequency. I will follow up with a second version that does that. As two separate sysfs attributes, maybe ? sysfs is supposed to provide one value per attribute. For the patch itself, I would find it better if you used is_visible to determine if the new attributes should be visible (and/or writable) instead of returning -EOPNOTSUPP. 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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