On Sun, Aug 27, 2017 at 3:30 PM, Linus Walleij <linus.walleij@xxxxxxxxxx> wrote: > 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. > SGTM. I'll see if my team can clean up the MFD-based FTDI driver and submit it upstream. >>>>> 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, I haven't been in the habit of looking in tools/. Guess I should be. > > 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
