Hi Marc, Ben, On Tue, 7 Dec 2010 12:30:11 +0000, Ben Dooks wrote: > On Tue, Dec 07, 2010 at 12:10:10PM +0000, Mark Brown wrote: > > On Tue, Dec 07, 2010 at 11:07:05AM +0100, Jean Delvare wrote: > > > The I2C specification explicitly describes both SDA and SCL as > > > bidirectional lines. An I2C master with a read-only SCL is thus not > > > compliant. If a slow slave stretches the clock, errors will happen, > > > so the bus can't be considered as reliable. > > > > > > Signed-off-by: Jean Delvare <khali@xxxxxxxxxxxx> > > > > It'd be good to also flag this via sysfs so that it's more readily > > visible to things like diagnostic tools. In what form do you expect this, and what do you expect diagnostic tools to do about it? I can't think of anything straightforward and useful. We could abuse one functionality flag for unreliable masters, but then this is a boolean flag, with no way to report the actual problem to the customer. And write-only SCL is only one thing they can do wrongly. > Could be, I wonder how many other hardware based adapters just don't > do this. Quite a few devices i've seen don't use it as they're generally > fast enough, or implement some other status polling system. I don't know either, and I didn't mean to provide a general solution to this problem as I have no clue so far that a general problem exists. This patch is in response to the thread started by Matthias Zacharias where we were troubleshooting his I2C bus problems. I just wanted to make sure that the same problem doesn't happen again, i.e. developers don't set getscl to NULL in the hope that it will help in any way. I don't know of that many pieces of hardware driven by i2c-algo-bit and not having a bidirectional SCL line. In fact I only know of the i2c-parport, i2c-parport-light and i2c-gpio drivers doing this, and then again, only for some of the supported devices. So I'm not sure there is much point in spending a lot of time on this. Or, to make it clearer, you can spend as much time as _you_ want on this, but I won't. I'm busy enough as is. -- Jean Delvare -- To unsubscribe from this list: send the line "unsubscribe linux-i2c" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
