On Tue, Oct 14, 2014 at 4:53 AM, Mark Roszko <mark.roszko@xxxxxxxxx> wrote: > > > 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. > > Ah, well right now you can have an i2c bus with driver 1 and 2. Say > the i2c bus is configured for 60khz in kernel space which normally > can't be changed. Driver 1 talks to a slave that cannot go above > 100khz. Now the userspace interface is added to the i2c bus. Some > userspace application decides to reconfigure the bus for 400khz and do > its communication to some slave device. Now the kernel tries to do > some background talking to the drive 1 slave and suddenly finds it can > no longer communicate with it. Right now with the kernel space only > configuration, the system is safe from being messed up easily. It's > more of a sanity of configuration issue. You need privileges to change the bus frequency, so this is a configuration issue. Which you still have today, since can still set the i2c frequency on some busses via a module parameter. > > > >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. > > I was actually thinking you could eliminate the table of supported > frequencies and just have the bus driver handle the set frequency > decision itself and just return an error code if it's invalid. There > are legitiamate drivers that cannot do more than a list of frequencies > already as well. One example is here: > http://lxr.free-electrons.com/source/drivers/i2c/busses/i2c-bcm-kona.c#L717 Yes, I will do that for v2 and in addition I will also add min and max attributes to make it easier to determine if a bus supports fast mode, fast plus, high, etc. -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
