On Tue, Jan 30, 2018 at 8:34 PM, Steven Presser <steve@xxxxxxxxxxxxx> wrote: > Andy, > > I apologize for the long response, but there's several issues to address > here. NP, it it a good explanation why. That's what commit message missed apparently. > First, I believe the "bmc150" in the subject line is in some way a misnomer. > You'd have to ask Jeremy for more details on what he intended it to refer > to. However, I believe the device in question is actually the bma250[1], > which does not have a magnetometer component. I'm unfortunately away from > my notes, but I can check later if you need me to verify the exact chip. Please do, I would really be on the safe side here. > Second, we're seeing a difference between what's in the data sheet and > what's exposed in the wild via ACPI. I own the laptop that started the > process of building this patch and I did the original ACPI-tables > investigation. > > The device in question (BOSC0200) appears in the Lenovo Yoga 11e (and > possibly other laptops - this happens to be the one I own). These laptops > have a 360-degree hinge between the screen and the keyboard, letting them > convert into tablets, if the user desires. The 11e implements this > mode-switching by placing an accelerometer in each of the screen and > keyboard, then doing math with the resulting vectors to figure out the angle > between the two. This makes a lot of sense. > For whatever reason, Lenovo chose to expose these two > (physically separate) accelerometers via a single ACPI device which presents > two i2c devices at sequential addresses. > As part of my original investigation of the Yoga 11e, I wrote a > proof-of-concept of pulling accelerometer data from the two devices exposed > under the BOSC0200 ID and using that to calculate the position of the screen > relative to the keyboard. So based on my empirical experience, I can tell > you the BOSC0200 device ID can expose two accelerometers at sequential > addresses in the wild. > > I don't understand why Lenovo has reused the BOSC0200 ACPI device ID for a > device that is fundamentally different from the base device. The ID doesn't > belong to them and we're (apparently) now stuck in this situation where this > ACPI device ID could represent two different device layouts. Bad, bad Lenovo. (DMI strings might help here) > Finally - Andy, I apologize if I came across as challenging you in my > initial mail. I was trying to strike a balance between brevity/respecting > your time and asking a question. Evidently I struck the wrong balance and > should have given you more background on why I was doubting what you saw. > This is my fault and you have my sincerest apologies for any offense I have > caused. No need, the root cause is lack of description in the commit message. Nevertheless, the approach chosen I don't like. It looks like an ugly hack. What we can do here is: - do not contaminate core part with I2C/SPI/etc - do not create another driver via board_info, we already in *the same* driver, so, the better approach here AFAICS is to add DMI quirk into i2c-core-acpi > Steve > > [1] > https://ae-bst.resource.bosch.com/media/_tech/media/datasheets/BST-BMA250E-DS004-06.pdf -- With Best Regards, Andy Shevchenko -- To unsubscribe from this list: send the line "unsubscribe linux-iio" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
