Using Mini UART on RPI CM
eric at anholt.net
Wed Sep 30 13:18:09 PDT 2015
Stefan Wahren <info at lategoodbye.de> writes:
> Hi Martin,
> i want to use both UARTs on a Raspberry Pi Compute Module. Yes, i know
> you still working on the driver, but i hope you can help me with an issue.
> I took this branch  from your repository and add "ns16550" to the
> compatible string of the uart1 node in bcm2835.dtsi
> Unfortunately i got an error during boot:
> [ 0.738732] Serial: 8250/16550 driver, 1 ports, IRQ sharing enabled
> [ 0.746685] of_serial 20215040.uart: clk or clock-frequency not defined
> [ 3.448517] of_serial: probe of 20215040.uart failed with error -22
> I narrowed down the problem to this sequence in of_platform_serial_setup():
> info->clk = devm_clk_get(&ofdev->dev, NULL);
> ret = clk_prepare_enable(info->clk);
> clk = clk_get_rate(info->clk);
> Finally the value of clk is zero, which leads to the error code 22
> (EINVAL). In the bcm2835.dtsi file there are two clocks defined for uart1:
> clocks = <&aux_clocks BCM2835_AUX_CLOCK_UART>, <&clocks
> After swapping both clocks in dtsi the problem disappears. But i think
> this is not the right way to fix this issue.
> Did i miss something in my board dts file to enable the aux uart clock?
That branch looks like it needs the submitted version of "Add a driver
for the auxiliary peripheral clock gates" instead, which I think would
fix this problem.
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