About new gpio API in linux/gpio.h adopted by kernel 4.8

[Andrew Jeffery]

On Thu, 6 Sep 2018, at 22:17, Andrew Geissler wrote:
> Hey Kuiying, this seems like more of a 4.18 kernel question for
> Joel/AndrewJ. Put them on cc.
> On Thu, Sep 6, 2018 at 2:30 AM Wang, Kuiying <kuiying.wang at intel.com> wrote:
> >
> > Hi Brad/Andrew,
> > I found the new gpio API adopted by kernel 4.8, is not fully ready, all the lines are "unnamed".

I expect this is because no-one has given them an name in your devicetree. For example, here's some output from a system I have handy:

root at witherspoon:/tmp# gpioinfo /dev/gpiochip3
gpiochip3 - 16 lines:
        line   0: "PS_SMBUS_RESET_N" unused input active-high 
        line   1: "APSS_RESET_N" unused input active-high 
        line   2: "GPU0_TH_OVERT_N_BUFF" unused input active-high 
        line   3: "GPU1_TH_OVERT_N_BUFF" unused input active-high 
        line   4: "GPU2_TH_OVERT_N_BUFF" unused input active-high 
        line   5: "GPU3_TH_OVERT_N_BUFF" unused input active-high 
        line   6: "GPU4_TH_OVERT_N_BUFF" unused input active-high 
        line   7: "GPU5_TH_OVERT_N_BUFF" unused input active-high 
        line   8: "GPU0_PWR_GOOD_BUFF" unused input active-high 
        line   9: "GPU1_PWR_GOOD_BUFF" unused input active-high 
        line  10: "GPU2_PWR_GOOD_BUFF" unused input active-high 
        line  11: "GPU3_PWR_GOOD_BUFF" unused input active-high 
        line  12: "GPU4_PWR_GOOD_BUFF" unused input active-high 
        line  13: "GPU5_PWR_GOOD_BUFF" unused input active-high 
        line  14: "12V_BREAKER_FLT_N" unused input active-high 
        line  15: "THROTTLE_UNLATCHED_N" unused input active-high

Which corresponds to:

https://github.com/openbmc/linux/blob/dev-4.18/arch/arm/boot/dts/aspeed-bmc-opp-witherspoon.dts#L501

> > If that we cannot switch to it now.
> > Or there is special kernel based configuration I have to do?
> >
> > root at wolfpass:/tmp# ./gpiodetect
> > gpiochip0 [SGPIOA] (8 lines)
> > gpiochip1 [SGPIOB] (8 lines)
> > gpiochip10 [1e780000.gpio] (232 lines)
> > gpiochip2 [SGPIOC] (8 lines)
> > gpiochip3 [SGPIOD] (8 lines)
> > gpiochip4 [SGPIOE] (8 lines)
> > gpiochip5 [SGPIOF] (8 lines)
> > gpiochip6 [SGPIOG] (8 lines)
> > gpiochip7 [SGPIOH] (8 lines)
> > gpiochip8 [SGPIOI] (8 lines)
> > gpiochip9 [SGPIOJ] (8 lines)
> > root at wolfpass:/tmp# ./gpioinfo /dev/gpiochip1
> > gpiochip1 - 8 lines:
> >         line   0:      unnamed       unused  output  active-high
> >         line   1:      unnamed       unused  output  active-high
> >         line   2:      unnamed       unused  output  active-high
> >         line   3:      unnamed       unused  output  active-high
> >         line   4:      unnamed       unused  output  active-high
> >         line   5:      unnamed       unused  output  active-high
> >         line   6:      unnamed       unused  output  active-high
> >         line   7:      unnamed       unused  output  active-high
> > root at wolfpass:/tmp# ./gpioinfo /dev/gpiochip10
> > gpiochip10 - 232 lines:
> >         line   0:      unnamed       unused   input  active-high
> >         line   1:      unnamed       unused   input  active-high
> >         line   2:      unnamed       unused   input  active-high
> >         line   3:      unnamed       unused   input  active-high
> >         line   4:      unnamed       unused   input  active-high
> >         line   5:      unnamed       unused   input  active-high
> >         line   6:      unnamed       unused   input  active-high
> >         line   7:      unnamed       unused   input  active-high
> >         line   8:      unnamed       unused   input  active-high
> >         line   9:      unnamed       unused   input  active-high
> >         line  10:      unnamed       unused   input  active-high
> >         line  11:      unnamed       unused   input  active-high
> >         line  12:      unnamed       unused   input  active-high
> >         line  13:      unnamed       unused   input  active-high
> >         line  14:      unnamed       unused   input  active-high
> >         line  15:      unnamed       unused   input  active-high
> >         line  16:      unnamed       unused   input  active-high
> > root at wolfpass:/tmp# ./gpioget /dev/gpiochip10 219
> > ./gpioget: error reading GPIO values: Device or resource busy
> >

This all works fine for me. Busy is because the GPIO has been exported through some other means, for example the sysfs interface:

root at witherspoon:/tmp# ls /sys/class/gpio
export       gpio305      gpio347      gpio417      gpiochip238  gpiochip280
gpio281      gpio306      gpio353      gpiochip222  gpiochip254  unexport
root at witherspoon:/tmp# gpioget /dev/gpiochip0 $((305 - 280))
gpioget: error reading GPIO values: Device or resource busy

Hope that helps.

Andrew