Re: [PATCH 1/2] spi: bcm2835: add spi-bcm2835aux driver for the auxiliar spi1 and spi2

On 24.07.2015, at 06:09, Stephen Warren [off-list ref] wrote:

I think I'd expect the shared registers to be:

bcm2835aux: misc@0x7e215000 {
   compatible = "brcm,bcm2835-aux";
   reg = <0x7e215000 0x08>;
};

There are two 4-byte registers outside the UART/SPI blocks, and the
compatible value should reflect what the block is, not that Linux may
use a syscon driver to implement the driver for it.

In the client, I'd expect a more semantic naming for the reference;
something like:

	brcm,aux = <&bcm2835aux 4>;

brcm, since it's a custom/vendor-specific property. aux is the name of
the object that's referenced. Packing the phandle and data together into
a single property reduces the number of separate properties, and is a
typical thing to do in a client of a service in DT.

So in the end you are saying we need a separate driver to get written
(because of ‘compatible = "brcm,bcm2835-aux”;’)

That is unless you would allow:
compatible = compatible = "brcm,bcm2835-aux”, “syscon”;

If this is not acceptable, then where should such a driver go in the
kernel tree?

It would essentially implement the following:
bcm2835aux_enable(dev, device-id);
bcm2835aux_disable(dev, device-id);

Which would just set/clean the bits in the register while holding a lock.

As an alternative: maybe we could implement it as an IRQ driver
and when the irq is requested for that device, then the HW-block gets
enabled automatically (and disabled when released).

That way we may not need to have a separate driver that would enable
the uart1, but it would be sufficient to configure it as follows:

uart1: uart@7e215040 {
	compatible = "brcm,bcm2835-aux-uart", "ns16550";
	reg = <0x7e215040 0x40>;
	interrupts = <X 0>;
	clock-frequency = <500000000>;
	reg-shift = <2>;
	no-loopback-test;
	status = "disabled";
};

(taken from the foundation device-tree)

Please clarify

Thanks,
Martin--
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