On Fri, Aug 25, 2017 at 6:52 PM, Rick Altherr <raltherr@xxxxxxxxxx> wrote: >> Incidentally, people are sending patches to expose the FTDI >> expanders as common GPIO chips under Linux, so we can >> internally in the kernel or from the usersapce character device >> access them as "some GPIOs". > > I know my team at Google has an internal patch for exactly that. FTDI > expanders are complicated as they can be used as UART, GPIO, I2C, SPI > depending on configuration. Our project was using a mix of I2C and > GPIO so I directly my team to approach it as an MFD. I'd like to see > all of these use cases handled by the kernel but I understand the > other viewpoint of relying on libusb for cross-platform compatiblity. Hm. I see. But I see people pushing the in-kernel method so I think it will eventually win out. >>>> In my worst nightmare they export GPIO lines using >>>> the horrid ABI in /sys/gpio/* >>> >>> https://sourceforge.net/p/openocd/code/ci/v0.10.0/tree/src/jtag/drivers/sysfsgpio.c >> >> Gnah! >> Whoever writes a slot-in replacement making the character device >> take precendence wins lots of karma. > > If they show up at Linux Plumbers or visit San Jose, I'll take them to > dinner. I didn't see any docs for the chardev in Documentation. I > _think_ I understand how it works from reading the relevant sections > of gpiolib.c but I can see how users end up using sysfs instead. I intended tools/gpio/* to be the documentation: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/gpio If we need more written documentation we can do it I guess, Yours, Linus Walleij -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
