Hardware detection

[DigitalSmile]

We need some type of code that handles of auto detection part. Three main purposes:

1. Provide debugging information if something goes wrong.
2. List all available periphery, that pi4j can consume.
3. Get rid of "context" code and autoload corresponding providers depending on interfaces found.

There still should be a way to override this behaviour, but the main reason is to simply API interfaces for a regular user and provide log messages with hints.
I can see a three way steps in detection process:

1. Scan live nodes of interfaces located at /dev/... and ioctl. Most of enabled interfaces will be detected.
2. Scan device tree to find potential interfaces, but disabled for some reason.
3. Fallback to ACPI search in sysfs for systems without device tree (e.g. x86 PC)

@eitch @FDelporte @stefanhaustein guys, what do you think?

[stefanhaustein]

From the user/API side, I think for each IO type (GPIO, SPI, I2C, PWM, ...) I'd expect a list of available configurations (bus number / bcm address -- initially I'd start with the absolute basics).

Does linux know the mapping to physical pins?

What I am wondering: Is there a way to know that I2C uses GPIO pins 1&2 -- i.e. is there a way to know that we can't use them for GPIO if I2C is enabled? Or does enabling I2C at the driver level block GPIO on these pins in any case?

[DigitalSmile]

Or does enabling I2C at the driver level block GPIO on these pins in any case?

It does. There is a label put on each line with application/driver used. E.g.

gpiochip4 - 54 lines:
	line   0:     "ID_SDA"       unused   input  active-high 
	line   1:     "ID_SCL"       unused   input  active-high 
	line   2:      "GPIO2"       unused   input  active-high 
	line   3:      "GPIO3"       unused   input  active-high 
	line   4:      "GPIO4"       unused   input  active-high 
	line   5:      "GPIO5"       unused   input  active-high 
	line   6:      "GPIO6"       unused   input  active-high 
	line   7:      "GPIO7"   "spi0 CS1"  output   active-low [used]
	line   8:      "GPIO8"   "spi0 CS0"  output   active-low [used]
	line   9:      "GPIO9"       unused   input  active-high 
	line  10:     "GPIO10"       unused   input  active-high 
	line  11:     "GPIO11"       unused   input  active-high 
	line  12:     "GPIO12"       unused   input  active-high 
	line  13:     "GPIO13"       unused   input  active-high 

[DigitalSmile]

Does linux know the mapping to physical pins?

I doubt it knows anything about physical world.

[stefanhaustein]

Do the line numbers have any meaning? Are these the pcm numbers?

Just to confirm: If I enable i2c in the rpi boot settings, the corresponding pins won't be available for gpio at all? Or just when I open I2c at runtime?

[DigitalSmile]

Do the line numbers have any meaning? Are these the pcm numbers?

They are configured in device tree to match special addresses in DMA controller. So it is very board specific and you always can add a device tree overlay to override this mapping.

Just to confirm: If I enable i2c in the rpi boot settings, the corresponding pins won't be available for gpio at all? Or just when I open I2c at runtime?

Yes, that's right. They will be occupied in boot time while parsing config.txt and device tree.