On 02/26/2016 11:19 AM, Eric Anholt wrote:

The BCM2835-ARM-Peripherals.pdf documentation specifies what the
function selects do for the pins, and there are a bunch of obvious
groupings to be made.  With these created, we'll be able to replace
bcm2835-rpi.dtsi's main "set all of these pins to alt0" with
references to specific groups we want enabled.

+			spi0_gpio7: spi0_gpio7 {
+				brcm,pins = <7 8 9 10 11>;
+				brcm,function = <BCM2835_FSEL_ALT0>;
+			};

This is too many pins.

- It includes both MOSI and MISO, although a particular use-case may 
only use 1 of those.

- It includes both chip-select signals, whereas a particular use-case 
may use 0, 1, or 2 of those. This is especially true since IIRC the 
mainline bcm283x SPI driver wants to only use GPIOs for chip-selects, 
not SPI-controller-generated chip-select signals, to avoid some issues 
with the HW generation of these signals.

I believe a similar comment applies to other SPI nodes too.

+			pcm_gpio18: pcm_gpio18 {
+				brcm,pins = <18 19 20 21>;
+				brcm,function = <BCM2835_FSEL_ALT0>;
+			};

Here too, I wonder if some people might want only one of DIN/DOUT and 
not both?

+			uart1_gpio36: uart1_gpio36 {
+				brcm,pins = <36 37 38 39>;
+				brcm,function = <BCM2835_FSEL_ALT2>;
+			};

Similarly, I think for UARTS, TX/RX and RTS/CTS should always be in 
different nodes so people can choose 2- or 4-wire mode. Most of the UART 
nodes are already split like this, but this one isn't.

+			emmc_gpio22: emmc_gpio22 {
+				brcm,pins = <22 23 24 25 26 27>;
+				brcm,function = <BCM2835_FSEL_ALT3>;
+			};

1-wire (1 data wire, plus CLK/CMD) eMMC is possible in theory, although 
I don't know whether it makes sense to support this?