On Mon, Mar 24, 2025 at 10:17:05AM -0700, Doug Anderson wrote: > On Mon, Mar 24, 2025 at 9:40 AM Laurent Pinchart wrote: > > On Tue, Mar 18, 2025 at 10:00:31PM +0100, Wolfram Sang wrote: > > > Hi Laurent, > > > > > > > > Read out and check the ID registers, so we can bail out if I2C > > > > > communication does not work or if the device is unknown. > > > > > > > > What's the advantage of that, what are you trying to guard against ? > > > > > > That a random chip at address 0x2c will be used. > > > > Is that really a problem ? That would only occur with a broken DT, is it > > worth guarding against a development-time issue with a runtime check > > that will increase boot time for every user ? > > FWIW, this can also happen simply due to broken / damaged hardware. If > a board gets stressed and causes a pin to become disconnected or if a > regulator ages and stops providing power then we can also end up in > this state. Getting a nice obvious error at probe when the device > isn't responding at all can make problems like this much easier to > debug.
I'm not fully convinced it's worth it, compared to an error at runtime, and especially given that there are way more pins than supplies or SCL/SDA that could suffer from a similar issue. I won't block the patch, but I think it's overkill. > It's not uncommon for i2c devices to probe to make sure the > device is really there at bootup. Checking for the full 8-byte ID is > probably a bit overkill, but at the same time if we're going to probe > something the ID is not a terrible thing to probe and reading 8 bytes > won't really take much longer than reading 1. -- Regards, Laurent Pinchart
