Missing GPIO line names for newer Raspberry Pi models

nikonthethird commented 5 years ago

The device tree (DTS) files for newer Raspberry Pi models (e.g. Raspberry Pi 3 B) are missing the GPIO line name definitions.

For instance, here are the line names for the Raspberry Pi B.

But in the corresponding file for the Raspberry Pi 3 B, there are no line names.

For reference, commit 731b26a6ac17f24057c559361c6d0cb7cb79baed introduced the line names.

The problem with the missing line names is that the gpioinfo utility prints this for a Raspberry Pi B:

gpiochip0 - 54 lines:
    line   0:       "SDA0"       unused   input  active-high
    line   1:       "SCL0"       unused   input  active-high
    line   2:       "SDA1"       unused   input  active-high
    line   3:       "SCL1"       unused   input  active-high
    line   4:  "GPIO_GCLK"       unused   input  active-high
    line   5:  "CAM_GPIO1"       unused   input  active-high
    line   6:    "LAN_RUN"       unused   input  active-high
    line   7:  "SPI_CE1_N"       unused   input  active-high
...

but this for a Raspberry Pi 3 B, which makes it hard to figure out which line is what:

gpiochip0 - 54 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
...

pelwell commented 5 years ago

The gpio-line-names feature is currently only present in the upstream DTS files (those named bcm28*), and even then only for a subset of models (A, A+, B, B+, Zero and ZeroW).

If it's any help, all Pis with the 40-pin header have exactly the same pin functions available on GPIOs 0-27. But beware - although pin functions are easily modified using DT overlays, the pinctrl mechanism for drivers and other utilities such as raspi-gpio, that list of GPIO names is completely static.

nikonthethird commented 5 years ago

Thank you, that does help.

I was just wondering, since the sysfs interface for GPIOs will be removed in 2020, then the only available interface for GPIOs will be the character device one, if the pin numbers will be the same.

So echo 26 > export is basically the same as exporting line offset 26 of gpio chip 0? Looking at the schematic, that seems to be the case.

pelwell commented 5 years ago

Yes, thank goodness - each gpiochip has a fixed numbering scheme (the Broadcom numbers for the on-board GPIOs), and the main gpiochip always seems to start at offset 0 in the global space.

N.B. gpiochip0 is named that way because it manages the global GPIO space starting at 0, so your statement above is trivially true, but it is also true that the onboard GPIO controller is always gpiochip0.

nikonthethird commented 5 years ago

That solves everything for me then. 👍

Feel free to close the issue since it seems to me now that the actual line names are not that important anyways.

seamusdemora commented 2 years ago

@pelwell ,

The gpio-line-names feature is currently only present in the upstream DTS files (those named bcm28*), and even then only for a subset of models (A, A+, B, B+, Zero and ZeroW).

If it's any help, all Pis with the 40-pin header have exactly the same pin functions available on GPIOs 0-27. But beware - although pin functions are easily modified using DT overlays, the pinctrl mechanism for drivers and other utilities such as raspi-gpio, that list of GPIO names is completely static.

I'm just beginning to explore the GPIO character device API. and discovered that gpioinfo provides only unnamed on my 3B+ (bullseye), but provides useful names on my 4B (buster). If I understand your input correctly, it seems that this is due to the fact that the pin names are absent from the dts file supplied for the 3B+... is that correct?

If so, can you point me to any documentation that explains where to find the applicable dts file for 3B+, and how to make these changes?

Another question wrt to the pinctrl mechanism: What are the implications of that if the names are added to the 3B+ dts?

Thanks!