svn commit: r323465 - head/usr.sbin/i2c

[Ian Lepore]

On Tue, 2017-10-10 at 19:20 +0300, Andriy Gapon wrote:
> On 10/10/2017 19:12, Ian Lepore wrote:
> > 
> > i2c -s is not a thing that's done routinely in a production system or
> > normal system operations... it's something a person does manually when
> > trying to configure or debug a system.  In that situation, there is
> > more harm in being told there are no working devices on the bus when in
> > fact everything is fine, than there is some some hypothetical device
> > doing some hypothetical "bad thing" in response to a read command.  In
> > all my years of working with i2c stuff I've never seen a device doing
> > anything more harmful than hanging the bus, requiring a reset (and even
> > causing that requires worse behavior than an unexpected read).  On the
> > other hand, I've seen a lot of people frustrated that i2c -s on freebsd
> > says there are no devices, while the equivelent command on linux shows
> > that everything is fine.
> Okay.
> 
> However, I will just mention that in the past I used to own a system where
> scanning the bus would make a slave that controlled CPU frequency to change it
> to some garbage.  The system "just" crashed, but theoretically the damage could
> have been worse.
> Also, I own a system right now where scanning the bus results in something like
> what you mentioned, but a little bit worse, the hanging bus that can be brought
> back only by a power cycle (not even a warm reset).
> 

These systems didn't used to hang on i2c -s, and now they do?

-- Ian