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    SubjectRe: [RFC PATCH v1 25/31] ARC: [plat-arcfpga] Hooking up platform to ARC UART
    Date
    On Monday 07 January 2013, Vineet Gupta wrote:
    > On Wednesday 07 November 2012 07:46 PM, Arnd Bergmann wrote:
    > > On Wednesday 07 November 2012, Vineet Gupta wrote:
    >
    > (1) Although I don't need the container "fpga" I'm forced to - because
    > of_platform_populate( ) -> of_match_node( ) expects the @match arg to be NOT NULL.
    > So we pass of_default_bus_match_table and have the compat string "simple-bus" in
    > the container. Per [1] it seemed it was possible to add the serial device directly
    > w/o the container.

    You could in theory make the serial port device itself be compatible to
    somthing that is being probed by of_platform_populate, but putting it
    under a bus is the preferred way. Usually each system has at least one
    bus that devices are connected to and I would recommend to represent all
    buses in the device tree like they are in hardware.

    > (2) I need the following OF_DEV_AUXDATA to be able to "name" the device correctly
    > so that the registered driver [4] can bind with device. How do I match the driver
    > and devicetree node w/o this glue - it seems compatible="<manuf>,<model>" is not
    > enough. This also requires the uart base address to be specified (otherwise
    > of_dev_lookup() fails to identify the auxdata) which IMHO defeats the purpose of
    > devicetree in first place.
    > b
    > static struct of_dev_auxdata arcuart_auxdata_lookup[] __initdata = {
    > OF_DEV_AUXDATA("snps,arc-uart", UART0_BASE, "arc-uart", arc_uart_info),
    > {}
    > };

    It should be enough to fill the drv->of_match_table member of the
    platform_driver with the match table.

    > (3) After above, driver's probe routine is getting called with platform_device->id
    > = -1 and it seems of_device_add() is doing that purposely. How do I handle that.

    What do you need the id for?

    > (4) Is above standalone "interrupts" string OK, or do I have to explicitly
    > instantiate the in-core intc as well. Since it is integral part of cpu, I really
    > don't need any support code to explicitly instantiate it. Also it is not accessed
    > via mem map - but special ARC instructions in aux address space of cpu.

    Interrupts are a little tricky. You need to create a bindind for your interrupt
    controller first and make the irqchip driver use irq domains in order for the
    irq description in the device tree to be mapped into a linux-internal irq number.

    In the simple case where you only have one irqchip in the system, you can use
    a "legacy" irq domain that simply translates the numbers 1:1. In some cases,
    it does make sense though (even with the legacy domain) to include additional
    flags in the device tree irq descriptor, e.g. the irq polarity and
    edge/level/message indication. Please read up on these and ask again if you have
    more questions.

    Arnd


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